AI Trajectory

null

{
  "EnableConfigs": [
    "SWAP",
    "ZSWAP",
    "USERFAULTFD",
    "SHMEM"
  ],
  "FocusSymbols": [
    "shmem_get_folio",
    "read_swap_cache_async",
    "swapin_readahead",
    "swap_retry_table_alloc",
    "swp_swapcount",
    "swap_put_entries_direct",
    "zswap_store",
    "zswap_load"
  ],
  "KMSANReasoning": "The patch updates the error handling of `get_swap_device()` to return an error pointer (`ERR_PTR(-EINVAL)`) for malformed swap entries, rather than just `NULL`. It updates various callers in the memory management subsystem (`mm/memory.c`, `mm/mincore.c`, `mm/shmem.c`, `mm/swap_state.c`, `mm/swapfile.c`, `mm/userfaultfd.c`, `mm/zswap.c`) to use `IS_ERR_OR_NULL()` and handle the error appropriately (e.g., returning `VM_FAULT_SIGBUS` in `do_swap_page()`). These changes address logic bugs and potential invalid memory accesses (which are well-covered by KASAN and standard kernel testing). There are no new data structures introduced, no modifications to user-space copy operations, and no changes that would expose uninitialized stack or heap memory. Therefore, KMSAN is not required.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch modifies `get_swap_device()` to return `ERR_PTR(-EINVAL)` instead of `NULL` for malformed swap entries. It updates multiple callers across memory management subsystems (core mm, shmem, mincore, swapfile, userfaultfd, zswap) to handle the new return type using `IS_ERR_OR_NULL()`. Notably, `do_swap_page()` now explicitly checks for `IS_ERR()` and returns `VM_FAULT_SIGBUS` instead of retrying, fixing a potential infinite page fault loop for malformed entries. This is a functional change in core kernel logic that is reachable from userspace and should be fuzzed.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 457f6d75f8d75a6177b9fb967997a8c5d1a677e5\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Aug 10 19:38:21 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/mm/memory.c b/mm/memory.c\nindex d9cf941967cf0..2842cd976f1d3 100644\n--- a/mm/memory.c\n+++ b/mm/memory.c\n@@ -4956,8 +4956,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)\n \n \t/* Prevent swapoff from happening to us. */\n \tsi = get_swap_device(entry);\n-\tif (unlikely(!si))\n+\tif (IS_ERR_OR_NULL(si)) {\n+\t\t/* A malformed entry never becomes valid, so don't retry it. */\n+\t\tif (IS_ERR(si))\n+\t\t\tret = VM_FAULT_SIGBUS;\n+\t\tsi = NULL;\n \t\tgoto out;\n+\t}\n \n \tfolio = swap_cache_get_folio(entry);\n \tif (folio)\ndiff --git a/mm/mincore.c b/mm/mincore.c\nindex ff4ac82817683..c086836bc4bcc 100644\n--- a/mm/mincore.c\n+++ b/mm/mincore.c\n@@ -71,7 +71,7 @@ static unsigned char mincore_swap(swp_entry_t entry, bool shmem)\n \t */\n \tif (shmem) {\n \t\tsi = get_swap_device(entry);\n-\t\tif (!si)\n+\t\tif (IS_ERR_OR_NULL(si))\n \t\t\treturn 0;\n \t}\n \tfolio = swap_cache_get_folio(entry);\ndiff --git a/mm/shmem.c b/mm/shmem.c\nindex 65572cbf1bd3c..d0a9f52bfed71 100644\n--- a/mm/shmem.c\n+++ b/mm/shmem.c\n@@ -2276,7 +2276,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,\n \n \tsi = get_swap_device(index_entry);\n \torder = shmem_confirm_swap(mapping, index, index_entry);\n-\tif (unlikely(!si)) {\n+\tif (IS_ERR_OR_NULL(si)) {\n \t\tif (order \u003c 0)\n \t\t\treturn -EEXIST;\n \t\telse\ndiff --git a/mm/swap_state.c b/mm/swap_state.c\nindex 4b7a3303c463b..f2e86d6626ecc 100644\n--- a/mm/swap_state.c\n+++ b/mm/swap_state.c\n@@ -715,7 +715,7 @@ struct folio *read_swap_cache_async(struct swap_io_ctx *ctx, swp_entry_t entry,\n \tstruct folio *folio;\n \n \tsi = get_swap_device(entry);\n-\tif (!si)\n+\tif (IS_ERR_OR_NULL(si))\n \t\treturn NULL;\n \n \tmpol = get_vma_policy(vma, addr, 0, \u0026ilx);\n@@ -951,7 +951,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,\n \t\t */\n \t\tif (swp_type(entry) != swp_type(targ_entry)) {\n \t\t\tsi = get_swap_device(entry);\n-\t\t\tif (!si)\n+\t\t\tif (IS_ERR_OR_NULL(si))\n \t\t\t\tcontinue;\n \t\t}\n \t\tfolio = swap_cache_read_folio(\u0026ctx, entry, gfp_mask, mpol, ilx,\ndiff --git a/mm/swapfile.c b/mm/swapfile.c\nindex 4d4e3e3059f6b..29612a0cf7afa 100644\n--- a/mm/swapfile.c\n+++ b/mm/swapfile.c\n@@ -1504,7 +1504,7 @@ int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp)\n \tunsigned long offset = swp_offset(entry);\n \n \tsi = get_swap_device(entry);\n-\tif (!si)\n+\tif (IS_ERR_OR_NULL(si))\n \t\treturn 0;\n \n \tci = __swap_offset_to_cluster(si, offset);\n@@ -1859,7 +1859,9 @@ void folio_put_swap(struct folio *folio, struct page *page)\n  * Check whether swap entry is valid in the swap device.  If so,\n  * return pointer to swap_info_struct, and keep the swap entry valid\n  * via preventing the swap device from being swapoff, until\n- * put_swap_device() is called.  Otherwise return NULL.\n+ * put_swap_device() is called.  Return NULL for an empty entry or a\n+ * device that is going away, and ERR_PTR(-EINVAL) if the entry itself\n+ * is malformed and can never name a slot on any device.\n  *\n  * Notice that swapoff or swapoff+swapon can still happen before the\n  * percpu_ref_tryget_live() in get_swap_device() or after the\n@@ -1899,13 +1901,14 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)\n \n \treturn si;\n bad_nofile:\n-\tpr_err(\"%s: %s%08lx\\n\", __func__, Bad_file, entry.val);\n+\tpr_err_ratelimited(\"%s: %s%08lx\\n\", __func__, Bad_file, entry.val);\n+\treturn ERR_PTR(-EINVAL);\n out:\n \treturn NULL;\n put_out:\n-\tpr_err(\"%s: %s%08lx\\n\", __func__, Bad_offset, entry.val);\n+\tpr_err_ratelimited(\"%s: %s%08lx\\n\", __func__, Bad_offset, entry.val);\n \tpercpu_ref_put(\u0026si-\u003eusers);\n-\treturn NULL;\n+\treturn ERR_PTR(-EINVAL);\n }\n \n /*\n@@ -2001,7 +2004,7 @@ int swp_swapcount(swp_entry_t entry)\n \tint count;\n \n \tsi = get_swap_device(entry);\n-\tif (!si)\n+\tif (IS_ERR_OR_NULL(si))\n \t\treturn 0;\n \n \tci = swap_cluster_lock(si, swp_offset(entry));\n@@ -2127,7 +2130,7 @@ void swap_put_entries_direct(swp_entry_t entry, int nr)\n \tstruct swap_info_struct *si;\n \n \tsi = get_swap_device(entry);\n-\tif (WARN_ON_ONCE(!si))\n+\tif (WARN_ON_ONCE(IS_ERR_OR_NULL(si)))\n \t\treturn;\n \tif (WARN_ON_ONCE(end_offset \u003e si-\u003emax))\n \t\tgoto out;\ndiff --git a/mm/userfaultfd.c b/mm/userfaultfd.c\nindex 24a4d92ffa3c2..bf7bc7fb1aa0f 100644\n--- a/mm/userfaultfd.c\n+++ b/mm/userfaultfd.c\n@@ -1700,7 +1700,8 @@ static long move_pages_ptes(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd\n \t\t}\n \n \t\tsi = get_swap_device(entry);\n-\t\tif (unlikely(!si)) {\n+\t\tif (IS_ERR_OR_NULL(si)) {\n+\t\t\tsi = NULL;\n \t\t\tret = -EAGAIN;\n \t\t\tgoto out;\n \t\t}\ndiff --git a/mm/zswap.c b/mm/zswap.c\nindex f7c9c89f6449c..bc9b931d6f447 100644\n--- a/mm/zswap.c\n+++ b/mm/zswap.c\n@@ -997,7 +997,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,\n \n \t/* try to allocate swap cache folio */\n \tsi = get_swap_device(swpentry);\n-\tif (!si)\n+\tif (IS_ERR_OR_NULL(si))\n \t\treturn -EEXIST;\n \n \tmpol = get_task_policy(current);\n"
}

best-expensive

null

{
  "EnableConfigs": [
    "SWAP",
    "ZSWAP",
    "USERFAULTFD",
    "SHMEM"
  ],
  "FocusSymbols": [
    "shmem_get_folio",
    "read_swap_cache_async",
    "swapin_readahead",
    "swap_retry_table_alloc",
    "swp_swapcount",
    "swap_put_entries_direct",
    "zswap_store",
    "zswap_load"
  ],
  "Reasoning": "The patch modifies `get_swap_device()` to return `ERR_PTR(-EINVAL)` instead of `NULL` for malformed swap entries. It updates multiple callers across memory management subsystems (core mm, shmem, mincore, swapfile, userfaultfd, zswap) to handle the new return type using `IS_ERR_OR_NULL()`. Notably, `do_swap_page()` now explicitly checks for `IS_ERR()` and returns `VM_FAULT_SIGBUS` instead of retrying, fixing a potential infinite page fault loop for malformed entries. This is a functional change in core kernel logic that is reachable from userspace and should be fuzzed.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
  even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).
- Code in vendor-specific PCIe switch, SmartNIC, or GPU drivers (e.g., mlxsw, pds_core, qed,
  ionic, amdgpu) that require physical PCIe hardware cards not emulated in standard QEMU.
- Driver .remove, .shutdown, or pci_unregister_driver teardown callbacks (e.g., igb_remove)
  that are executed only during PCI hot-unplug or sysfs driver unbind operations.

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
   Prefer non-static, non-inlined API entrypoint functions over internal static helper functions
   (which are inlined by the compiler and do not have distinct symbol addresses).
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Also check "depends on" lines in Kconfig to include any non-standard parent subsystem configs
   needed for Kbuild to compile the code statically into vmlinux. List them in the EnableConfigs
   output array, and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 457f6d75f8d75a6177b9fb967997a8c5d1a677e5
Author: syz-cluster <triage@syzkaller.com>
Date:   Mon Aug 10 19:38:21 2026 +0000

    syz-cluster: applied patch under review

diff --git a/mm/memory.c b/mm/memory.c
index d9cf941967cf0..2842cd976f1d3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4956,8 +4956,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 	/* Prevent swapoff from happening to us. */
 	si = get_swap_device(entry);
-	if (unlikely(!si))
+	if (IS_ERR_OR_NULL(si)) {
+		/* A malformed entry never becomes valid, so don't retry it. */
+		if (IS_ERR(si))
+			ret = VM_FAULT_SIGBUS;
+		si = NULL;
 		goto out;
+	}
 
 	folio = swap_cache_get_folio(entry);
 	if (folio)
diff --git a/mm/mincore.c b/mm/mincore.c
index ff4ac82817683..c086836bc4bcc 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -71,7 +71,7 @@ static unsigned char mincore_swap(swp_entry_t entry, bool shmem)
 	 */
 	if (shmem) {
 		si = get_swap_device(entry);
-		if (!si)
+		if (IS_ERR_OR_NULL(si))
 			return 0;
 	}
 	folio = swap_cache_get_folio(entry);
diff --git a/mm/shmem.c b/mm/shmem.c
index 65572cbf1bd3c..d0a9f52bfed71 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2276,7 +2276,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 
 	si = get_swap_device(index_entry);
 	order = shmem_confirm_swap(mapping, index, index_entry);
-	if (unlikely(!si)) {
+	if (IS_ERR_OR_NULL(si)) {
 		if (order < 0)
 			return -EEXIST;
 		else
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 4b7a3303c463b..f2e86d6626ecc 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -715,7 +715,7 @@ struct folio *read_swap_cache_async(struct swap_io_ctx *ctx, swp_entry_t entry,
 	struct folio *folio;
 
 	si = get_swap_device(entry);
-	if (!si)
+	if (IS_ERR_OR_NULL(si))
 		return NULL;
 
 	mpol = get_vma_policy(vma, addr, 0, &ilx);
@@ -951,7 +951,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 		 */
 		if (swp_type(entry) != swp_type(targ_entry)) {
 			si = get_swap_device(entry);
-			if (!si)
+			if (IS_ERR_OR_NULL(si))
 				continue;
 		}
 		folio = swap_cache_read_folio(&ctx, entry, gfp_mask, mpol, ilx,
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4d4e3e3059f6b..29612a0cf7afa 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1504,7 +1504,7 @@ int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp)
 	unsigned long offset = swp_offset(entry);
 
 	si = get_swap_device(entry);
-	if (!si)
+	if (IS_ERR_OR_NULL(si))
 		return 0;
 
 	ci = __swap_offset_to_cluster(si, offset);
@@ -1859,7 +1859,9 @@ void folio_put_swap(struct folio *folio, struct page *page)
  * Check whether swap entry is valid in the swap device.  If so,
  * return pointer to swap_info_struct, and keep the swap entry valid
  * via preventing the swap device from being swapoff, until
- * put_swap_device() is called.  Otherwise return NULL.
+ * put_swap_device() is called.  Return NULL for an empty entry or a
+ * device that is going away, and ERR_PTR(-EINVAL) if the entry itself
+ * is malformed and can never name a slot on any device.
  *
  * Notice that swapoff or swapoff+swapon can still happen before the
  * percpu_ref_tryget_live() in get_swap_device() or after the
@@ -1899,13 +1901,14 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)
 
 	return si;
 bad_nofile:
-	pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_file, entry.val);
+	return ERR_PTR(-EINVAL);
 out:
 	return NULL;
 put_out:
-	pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
 	percpu_ref_put(&si->users);
-	return NULL;
+	return ERR_PTR(-EINVAL);
 }
 
 /*
@@ -2001,7 +2004,7 @@ int swp_swapcount(swp_entry_t entry)
 	int count;
 
 	si = get_swap_device(entry);
-	if (!si)
+	if (IS_ERR_OR_NULL(si))
 		return 0;
 
 	ci = swap_cluster_lock(si, swp_offset(entry));
@@ -2127,7 +2130,7 @@ void swap_put_entries_direct(swp_entry_t entry, int nr)
 	struct swap_info_struct *si;
 
 	si = get_swap_device(entry);
-	if (WARN_ON_ONCE(!si))
+	if (WARN_ON_ONCE(IS_ERR_OR_NULL(si)))
 		return;
 	if (WARN_ON_ONCE(end_offset > si->max))
 		goto out;
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 24a4d92ffa3c2..bf7bc7fb1aa0f 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1700,7 +1700,8 @@ static long move_pages_ptes(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd
 		}
 
 		si = get_swap_device(entry);
-		if (unlikely(!si)) {
+		if (IS_ERR_OR_NULL(si)) {
+			si = NULL;
 			ret = -EAGAIN;
 			goto out;
 		}
diff --git a/mm/zswap.c b/mm/zswap.c
index f7c9c89f6449c..bc9b931d6f447 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -997,7 +997,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 
 	/* try to allocate swap cache folio */
 	si = get_swap_device(swpentry);
-	if (!si)
+	if (IS_ERR_OR_NULL(si))
 		return -EEXIST;
 
 	mpol = get_task_policy(current);

gemini-3.1-pro-preview

null

null

							input: 4002
							output: 36
							thoughts: 711
						

**Analyzing a Swap Handling Patch**

Okay, so I'm looking at this patch that's tweaking some swap handling code, specifically around how we deal with those potentially nasty malformed swap entries. It looks like the core change is in `get_swap_device()`, where it's now returning `ERR_PTR(-EINVAL)` instead of `NULL` for these bad entries. This subtle shift has a ripple effect, forcing a bunch of callers in `mm/` to update their checks to use `IS_ERR_OR_NULL(si)`. Smart move, catches all cases.

The `do_swap_page()` function in `mm/memory.c` is the most interesting part. The patch explicitly addresses `IS_ERR(si)` by returning `VM_FAULT_SIGBUS`. This is a pretty significant functional change because now, instead of just silently failing and potentially looping forever on a page fault, we're explicitly signaling a bus error. This is much better, and really worth fuzzing!

Let's see… Modified functions are: `do_swap_page`, `mincore_swap`, `shmem_swapin_folio`, `read_swap_cache_async`, `swap_vma_readahead`, `swap_retry_table_alloc`, `get_swap_device`, `swp_swapcount`, `swap_put_entries_direct`, `move_pages_ptes`, and `zswap_writeback_entry`. Okay, that gives us a good overview.

I need to focus my fuzzing efforts. `do_swap_page` is definitely hot, but the patch's main change is in error handling. `get_swap_device` is also hot, but handling of malformed swap entries is the target here. Then we have `move_pages_ptes` (userfaultfd) and `zswap_writeback_entry` (zswap). `shmem_swapin_folio` is related to shmem.

Okay, let's zoom in on `get_swap_device` and its callers. The key here is the handling of *malformed* entries. My gut tells me user space is where this vulnerability will likely be found. So, it's those `madvise` calls and userfaultfd that are potential vectors for introducing bad entries. If `get_swap_device` returned `NULL` before, `do_swap_page` just skipped and returned 0 (possibly leading to infinite loop). Now it causes a SIGBUS. That's a good change.

Let me think about the config options. `CONFIG_SWAP` is obviously required for swap support, `CONFIG_ZSWAP` for zswap, `CONFIG_USERFAULTFD` for userfaultfd, and `CONFIG_SHMEM` for shmem. I should check `mm/swapfile.c` and `mm/memory.c` to see if they depend on `CONFIG_SWAP`. Yep, `mm/swapfile.c` is compiled under `CONFIG_SWAP`. `mm/memory.c` is always compiled. Time for a quick grep.

{
  "Expression": "^vm_fault_t do_swap_page",
  "PathPrefix": "mm/memory.c"
}

{
  "Output": "mm/memory.c=4863=static void check_swap_exclusive(struct folio *folio, swp_entry_t entry,\n--\nmm/memory.c-4880- */\nmm/memory.c:4881:vm_fault_t do_swap_page(struct vm_fault *vmf)\nmm/memory.c-4882-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 5520
							output: 29
							thoughts: 21
						

Okay, here's my summary, considering my expertise:

**Checking Swap Page Functionality**

Right, let's just make absolutely sure that `do_swap_page` is only included when swap support is actually enabled. This is crucial for maintainability and preventing build issues. I need to quickly verify that `#ifdef CONFIG_SWAP` correctly encapsulates the `do_swap_page` function definition. It's a fundamental check, really. If it's *not* properly guarded, the kernel might attempt to call swap-related functions even when the configuration is set to disable swapping, leading to potentially nasty errors or incorrect behavior. So, let's delve into the code and confirm that the preprocessor directive is doing its job as expected. This should be a trivial check, but it's a critical one for keeping the system stable and properly configured. No shortcuts here!

no matches

{
  "Expression": "CONFIG_SWAP",
  "PathPrefix": "mm/memory.c"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 5768
							output: 24
							thoughts: 36
						

Okay, here's my take on those thoughts, framed as my own mental process:

**Deeper Dive into `do_swap_page` Location**

Hmm, something doesn't feel right. I was under the impression that the `do_swap_page` function resided in `mm/memory.c` and was conditionally compiled with `CONFIG_SWAP`. But a quick glance at the code is indicating this might not be accurate. I should double check the build configuration and the surrounding Makefile to confirm the exact location and conditional compilation of that function. Let me go back and investigate the build process in `mm/Makefile`. That should give me the definitive answer and resolve this discrepancy quickly. I need to be sure before I move forward, and the Makefile is the source of truth for the build.

{
  "Expression": "swap",
  "PathPrefix": "mm/Makefile"
}

{
  "Output": "mm/Makefile=76=endif\nmm/Makefile-77-\nmm/Makefile:78:obj-$(CONFIG_SWAP)\t+= page_io.o swap_state.o swapfile.o\nmm/Makefile:79:obj-$(CONFIG_ZSWAP)\t+= zswap.o\nmm/Makefile-80-obj-$(CONFIG_HAS_DMA)\t+= dmapool.o\n"
}

gemini-3.1-pro-preview

null

null

							input: 6103
							output: 30
							thoughts: 57
						

Okay, let's break this down.

**Analyzing Swap Page Functionality in the Kernel**

Right, so `mm/memory.c` is definitely a core file, that's a given. It's always part of the build. Now, the `do_swap_page` function... that's where things get interesting. I'm pretty sure it's not always actively *used*, but rather conditionally compiled based on whether swap is enabled in the system configuration. Either that, or it's always compiled but only *called* if swapping is enabled. To be certain, I should just go and check directly in `mm/memory.c` and see how `do_swap_page` is handled there. That'll clear things up. No need to rely on assumptions when the source is right here.

{
  "Expression": "do_swap_page",
  "PathPrefix": "mm/memory.c"
}

{
  "Output": "mm/memory.c=947=static void restore_exclusive_pte(struct vm_area_struct *vma,\n--\nmm/memory.c-961-\nmm/memory.c:962:\t/* See do_swap_page(): restore PAGE_NONE for RWP */\nmm/memory.c-963-\tif (pte_swp_uffd(orig_pte) \u0026\u0026 userfaultfd_rwp(vma))\n--\nmm/memory.c=3652=int apply_to_existing_page_range(struct mm_struct *mm, unsigned long addr,\n--\nmm/memory.c-3661- * or configurations (e.g. i386 with PAE) which might give a mix of unmatched\nmm/memory.c:3662: * parts, do_swap_page must check under lock before unmapping the pte and\nmm/memory.c-3663- * proceeding (but do_wp_page is only called after already making such a check;\n--\nmm/memory.c=4795=static unsigned long thp_swapin_suitable_orders(struct vm_fault *vmf)\n--\nmm/memory.c-4839-\t/*\nmm/memory.c:4840:\t * For do_swap_page, find the highest order where the aligned range is\nmm/memory.c-4841-\t * completely swap entries with contiguous swap offsets.\n--\nmm/memory.c=4863=static void check_swap_exclusive(struct folio *folio, swp_entry_t entry,\n--\nmm/memory.c-4880- */\nmm/memory.c:4881:vm_fault_t do_swap_page(struct vm_fault *vmf)\nmm/memory.c-4882-{\n--\nmm/memory.c-5230-\tset_ptes(vma-\u003evm_mm, address, ptep, pte, nr_pages);\nmm/memory.c:5231:\tarch_do_swap_page_nr(vma-\u003evm_mm, vma, address,\nmm/memory.c-5232-\t\t\tpte, pte, nr_pages);\n--\nmm/memory.c=6520=static vm_fault_t handle_pte_fault(struct vm_fault *vmf)\n--\nmm/memory.c-6566-\tif (!pte_present(vmf-\u003eorig_pte))\nmm/memory.c:6567:\t\treturn do_swap_page(vmf);\nmm/memory.c-6568-\n"
}

gemini-3.1-pro-preview

null

null

							input: 7008
							output: 32
							thoughts: 70
						

Okay, let's break this down.

**Investigating Swap Page Compilation**

Right, so `do_swap_page` is always compiled, that much is clear. But what about `get_swap_device`? That function's buried in `mm/swapfile.c`, which makes me think it's conditionally compiled. Since it deals with swap files, my guess is it is controlled by `CONFIG_SWAP`. But I need to confirm this quickly. Best way to verify would be to check `include/linux/swap.h` and confirm that the function declaration is controlled by the appropriate preprocessor macro. Time to dig into that header file.

{
  "Expression": "get_swap_device",
  "PathPrefix": "include/linux/swap.h"
}

{
  "Output": "include/linux/swap.h=384=extern int swp_swapcount(swp_entry_t entry);\ninclude/linux/swap.h:385:extern struct swap_info_struct *get_swap_device(swp_entry_t entry);\ninclude/linux/swap.h-386-sector_t swap_folio_sector(struct folio *folio);\n--\ninclude/linux/swap.h=411=static inline void put_swap_device(struct swap_info_struct *si)\n--\ninclude/linux/swap.h-416-#else /* CONFIG_SWAP */\ninclude/linux/swap.h:417:static inline struct swap_info_struct *get_swap_device(swp_entry_t entry)\ninclude/linux/swap.h-418-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 7458
							output: 30
							thoughts: 588
						

**Analyzing Kernel Swap and Userfaultfd Symbol Coverage**

Okay, so I'm digging into this patch. First things first, `CONFIG_SWAP` is a given; it's fundamental to the topic. Now, I see modifications to `mm/zswap.c` and `mm/userfaultfd.c`. This means I need to account for `CONFIG_ZSWAP` and `CONFIG_USERFAULTFD` as well.

To get a handle on what the patch is touching, I need to list the relevant configurations and symbols. My config list is: `SWAP`, `ZSWAP`, and `USERFAULTFD`. The symbols being modified are: `do_swap_page`, `mincore_swap`, `shmem_swapin_folio`, `read_swap_cache_async`, `swap_vma_readahead`, `swap_retry_table_alloc`, `get_swap_device`, `swp_swapcount`, `swap_put_entries_direct`, `move_pages_ptes`, and `zswap_writeback_entry`.

Hold on... I need to be careful with the instruction set. The instructions tell me to "Avoid listing generic hot-path functions to prevent skewed test distributions." Both `do_swap_page` and `get_swap_device` are definitely hot paths, especially when swap is heavily used. I should exclude those.

So, I'm going to focus on these symbols instead: `mincore_swap`, `shmem_swapin_folio`, `read_swap_cache_async`, `swap_vma_readahead`, `swap_retry_table_alloc`, `swp_swapcount`, `swap_put_entries_direct`, `move_pages_ptes`, and `zswap_writeback_entry`. These seem to be less frequently used, which is better for the testing instructions.

Before I go any further, I'll double-check to make sure `mincore_swap` isn't static.

{
  "Expression": "mincore_swap",
  "PathPrefix": "mm/mincore.c"
}

{
  "Output": "mm/mincore.c=27=static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,\n--\nmm/mincore.c-47-\nmm/mincore.c:48:static unsigned char mincore_swap(swp_entry_t entry, bool shmem)\nmm/mincore.c-49-{\n--\nmm/mincore.c=94=static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)\n--\nmm/mincore.c-111-\t\t\treturn 0;\nmm/mincore.c:112:\t\treturn mincore_swap(radix_to_swp_entry(folio), true);\nmm/mincore.c-113-\t}\n--\nmm/mincore.c=162=static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,\n--\nmm/mincore.c-205-\nmm/mincore.c:206:\t\t\t*vec = mincore_swap(entry, false);\nmm/mincore.c-207-\t\t}\n"
}

gemini-3.1-pro-preview

null

null

							input: 8803
							output: 33
							thoughts: 116
						

**Analyzing the `mincore` API Choices**

Okay, so I'm looking at this `mincore_swap` function and the code guidelines are pretty clear: avoid static, inlined helper functions if there's a non-static, non-inlined API entrypoint. The advice is to prefer functions with distinct symbol addresses, making them easier to trace and debug, right? So, `mincore_swap` is off the table as the preferred option.

Let's see, what are the alternatives? Ah, there's `mincore_pte_range` and `mincore_page`, or just the `mincore` system call entry itself – the one that hits the kernel directly. Wait a minute... `mincore_pte_range` is static as well? That's not helpful at all!

Alright, it looks like `sys_mincore` is the entry point we should be investigating further. That's the one we want to target.

Now, let's switch gears and examine what's going on with `shmem_swapin_folio`.

{
  "Expression": "shmem_swapin_folio",
  "PathPrefix": "mm/shmem.c"
}

{
  "Output": "mm/shmem.c=151=static unsigned long shmem_default_max_inodes(void)\n--\nmm/shmem.c-159-\nmm/shmem.c:160:static int shmem_swapin_folio(struct inode *inode, pgoff_t index,\nmm/shmem.c-161-\t\t\tstruct folio **foliop, enum sgp_type sgp, gfp_t gfp,\n--\nmm/shmem.c=1496=static int shmem_unuse_swap_entries(struct inode *inode,\n--\nmm/shmem.c-1506-\nmm/shmem.c:1507:\t\terror = shmem_swapin_folio(inode, indices[i], \u0026folio, SGP_CACHE,\nmm/shmem.c-1508-\t\t\t\t\tmapping_gfp_mask(mapping), NULL, NULL);\n--\nmm/shmem.c=2175=static int shmem_split_large_entry(struct inode *inode, pgoff_t index,\n--\nmm/shmem.c-2252- */\nmm/shmem.c:2253:static int shmem_swapin_folio(struct inode *inode, pgoff_t index,\nmm/shmem.c-2254-\t\t\t     struct folio **foliop, enum sgp_type sgp,\n--\nmm/shmem.c=2427=static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,\n--\nmm/shmem.c-2459-\tif (xa_is_value(folio)) {\nmm/shmem.c:2460:\t\terror = shmem_swapin_folio(inode, index, \u0026folio,\nmm/shmem.c-2461-\t\t\t\t\t   sgp, gfp, vmf, fault_type);\n"
}

gemini-3.1-pro-preview

null

null

							input: 9658
							output: 35
							thoughts: 29
						

Here's a summary of my understanding:

**Static Function Interaction**

Okay, so I've just been looking at some code and I've zeroed in on the relationship between two specific functions. I've noticed that `shmem_swapin_folio` is declared as a static function. That immediately tells me it's not meant to be directly called from anywhere outside its own compilation unit. Its visibility is deliberately restricted, which indicates a potentially internal implementation detail or optimization. Now, the caller that actually uses `shmem_swapin_folio`, the one I *can* see from outside that limited scope, is `shmem_get_folio_gfp`. This likely means `shmem_get_folio_gfp` is the public entry point for whatever functionality `shmem_swapin_folio` implements, perhaps acting as a wrapper or a manager for the underlying, static operation. I need to dig into the details of what `shmem_get_folio_gfp` does, it’s probably adding some context, checking preconditions, or providing a higher level abstraction. I'll bet it handles memory allocation flags (gfp) somehow, based on its name.

{
  "Expression": "shmem_get_folio_gfp",
  "PathPrefix": "mm/shmem.c"
}

{
  "Output": "mm/shmem.c=2042=static struct folio *shmem_swap_alloc_folio(struct inode *inode,\n--\nmm/shmem.c-2072- * When a page is moved from swapcache to shmem filecache (either by the\nmm/shmem.c:2073: * usual swapin of shmem_get_folio_gfp(), or by the less common swapoff of\nmm/shmem.c-2074- * shmem_unuse_inode()), it may have been read in earlier from swap, in\n--\nmm/shmem.c=2253=static int shmem_swapin_folio(struct inode *inode, pgoff_t index,\n--\nmm/shmem.c-2418-/*\nmm/shmem.c:2419: * shmem_get_folio_gfp - find page in cache, or get from swap, or allocate\nmm/shmem.c-2420- *\n--\nmm/shmem.c-2426- */\nmm/shmem.c:2427:static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,\nmm/shmem.c-2428-\t\tloff_t write_end, struct folio **foliop, enum sgp_type sgp,\n--\nmm/shmem.c=2630=int shmem_get_folio(struct inode *inode, pgoff_t index, loff_t write_end,\n--\nmm/shmem.c-2632-{\nmm/shmem.c:2633:\treturn shmem_get_folio_gfp(inode, index, write_end, foliop, sgp,\nmm/shmem.c-2634-\t\t\tmapping_gfp_mask(inode-\u003ei_mapping), NULL, NULL);\n--\nmm/shmem.c=2709=static vm_fault_t shmem_fault(struct vm_fault *vmf)\n--\nmm/shmem.c-2727-\tWARN_ON_ONCE(vmf-\u003epage != NULL);\nmm/shmem.c:2728:\terr = shmem_get_folio_gfp(inode, vmf-\u003epgoff, 0, \u0026folio, SGP_CACHE,\nmm/shmem.c-2729-\t\t\t\t  gfp, vmf, \u0026ret);\n--\nmm/shmem.c=5956=struct folio *shmem_read_folio_gfp(struct address_space *mapping,\n--\nmm/shmem.c-5963-\nmm/shmem.c:5964:\terror = shmem_get_folio_gfp(inode, index, i_size_read(inode),\nmm/shmem.c-5965-\t\t\t\t    \u0026folio, SGP_CACHE, gfp, NULL, NULL);\n"
}

gemini-3.1-pro-preview

null

null

							input: 10689
							output: 34
							thoughts: 27
						

Okay, here's my take on those thoughts, framed as an expert's internal monologue:

**Investigating `shmem_get_folio` and Async Swap Reads**

Right, `shmem_get_folio` isn't static. That immediately flags a potential area of wider usage and, therefore, a wider impact for any changes. Okay, that's good to keep in mind; the scope of this is likely not isolated to a small module. I need to understand what this function does and where it's being used to truly comprehend its importance, but the `non-static` immediately gives me a perspective I need to consider.

Now, where was I? Right, I should look at `read_swap_cache_async`. This one likely interfaces with the swap cache and deals with asynchronous reads, which means it probably interacts with `shmem_get_folio` in ways that affect performance or concurrency. Let me refresh my memory on the interactions here. I bet there's some interesting nuance in how the async read is kicked off, how the folio is handled, and how that interacts with the overall page cache mechanics and I/O scheduler. This could be a good line of enquiry to figure out the use of `shmem_get_folio`.

{
  "Expression": "read_swap_cache_async",
  "PathPrefix": "mm/swap_state.c"
}

{
  "Output": "mm/swap_state.c=682=struct folio *swapin_sync(swp_entry_t entry, gfp_t gfp, unsigned long orders,\n--\nmm/swap_state.c-708- */\nmm/swap_state.c:709:struct folio *read_swap_cache_async(struct swap_io_ctx *ctx, swp_entry_t entry,\nmm/swap_state.c-710-\t\tgfp_t gfp_mask, struct vm_area_struct *vma, unsigned long addr)\n"
}

gemini-3.1-pro-preview

null

null

							input: 11161
							output: 34
							thoughts: 28
						

Here's my summary, as the thought process unfolds:

**Digging into `read_swap_cache_async`**

Okay, so `read_swap_cache_async` isn't static. That's good to know, means it's likely used externally. Now, I should probably check how it's being used. I will look at the `swap_vma_readahead` function, as that seems like a logical next step to understand the flow.

{
  "Expression": "swap_vma_readahead",
  "PathPrefix": "mm/swap_state.c"
}

{
  "Output": "mm/swap_state.c=860=static int swap_vma_ra_win(struct vm_fault *vmf, unsigned long *start,\n--\nmm/swap_state.c-898-/**\nmm/swap_state.c:899: * swap_vma_readahead - swap in pages in hope we need them soon\nmm/swap_state.c-900- * @targ_entry: swap entry of the targeted memory\n--\nmm/swap_state.c-913- */\nmm/swap_state.c:914:static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,\nmm/swap_state.c-915-\t\tstruct mempolicy *mpol, pgoff_t targ_ilx, struct vm_fault *vmf)\n--\nmm/swap_state.c=986=struct folio *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,\n--\nmm/swap_state.c-994-\tfolio = swap_use_vma_readahead() ?\nmm/swap_state.c:995:\t\tswap_vma_readahead(entry, gfp_mask, mpol, ilx, vmf) :\nmm/swap_state.c-996-\t\tswap_cluster_readahead(entry, gfp_mask, mpol, ilx);\n"
}

gemini-3.1-pro-preview

null

null

							input: 11690
							output: 33
							thoughts: 38
						

Okay, here's my interpretation of those thoughts, presented as my own mental process:

**Diving into Readahead and Swap Operations**

Alright, let's see... so, `swap_vma_readahead` is defined as a static function.  That means it's limited in scope, likely internal to a specific file or module.  On the other hand, `swapin_readahead` is *not* static, which gives it broader visibility and probably a different purpose. Interesting. I need to understand how these relate, specifically regarding readahead operations during swapping. The contrasting visibility levels of these functions has me curious about their roles. I bet it is important to the overall process.

Now, where do I start my deeper investigation? Let's check `swap_retry_table_alloc`. That seems like a logical next step. It's probably connected to how we manage memory during those swap operations, and could illuminate the conditions that would require read-ahead functions. Knowing its purpose will likely provide insights into how `swap_vma_readahead` and `swapin_readahead` are used, and why their scopes are different.

{
  "Expression": "swap_retry_table_alloc",
  "PathPrefix": "mm/swapfile.c"
}

{
  "Output": "mm/swapfile.c=1463=static int swap_extend_table_alloc(struct swap_info_struct *si,\n--\nmm/swapfile.c-1498-\nmm/swapfile.c:1499:int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp)\nmm/swapfile.c-1500-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 12115
							output: 31
							thoughts: 26
						

Here's my take on those thoughts:

**Analyzing `swap_retry_table_alloc` and `swp_swapcount`**

Okay, so `swap_retry_table_alloc` isn't static, which immediately sparks a thought process. Non-static functions usually imply a wider scope, potentially making them accessible from other parts of the kernel, or at least other modules. That has implications for how it's used and the potential for interactions with other code. This means I need to consider its usage context more broadly, beyond just the immediate scope.

Now, let me shift gears and check into the `swp_swapcount` variable, it is important here. I need to refresh my understanding of how those are related and why this is important at this stage. It is likely that both relate to the allocation strategy for swapping processes.

I'm thinking about how the allocation table is used with the swap counter. I need to connect this.

{
  "Expression": "swp_swapcount",
  "PathPrefix": "mm/swapfile.c"
}

{
  "Output": "mm/swapfile.c=1982=bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry)\n--\nmm/swapfile.c-1998- */\nmm/swapfile.c:1999:int swp_swapcount(swp_entry_t entry)\nmm/swapfile.c-2000-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 12480
							output: 33
							thoughts: 26
						

Here's my take on the thought process, as if it were my own:

**Investigating a Non-Static Swap Counter**

Okay, so `swp_swapcount` is declared non-static. Interesting. That immediately raises questions about its scope and potential for modification from different parts of the kernel. I need to understand its lifecycle and usage to see if this is an area where concurrency could lead to subtle issues, or if it's intentionally designed this way for some valid reason.

To dig deeper, let's start by examining how this counter is actually being used. Specifically, I'll check the `swap_put_entries_direct` function. This seems like a reasonable place to start, as the name suggests it deals with putting entries into swap, so it's likely a place where the swap counter might be touched. I expect to see the counter incremented or decremented in that function if it is being used to track the number of swap entries. From there I can follow the call graph to see what is calling it and gain more context.

{
  "Expression": "swap_put_entries_direct",
  "PathPrefix": "mm/swapfile.c"
}

{
  "Output": "mm/swapfile.c=1740=int folio_alloc_swap(struct folio *folio)\n--\nmm/swapfile.c-1800- * NOTE: The caller also has to ensure there is no raced call to\nmm/swapfile.c:1801: * swap_put_entries_direct on its swap entry before this helper returns, or\nmm/swapfile.c-1802- * the swap count may underflow.\n--\nmm/swapfile.c=1999=int swp_swapcount(swp_entry_t entry)\n--\nmm/swapfile.c-2026- * only be done by folio_dup_swap, which also locks the folio. But a concurrent\nmm/swapfile.c:2027: * decrease of swap count is possible through swap_put_entries_direct, so this\nmm/swapfile.c-2028- * may return a false positive.\n--\nmm/swapfile.c=2100=bool folio_free_swap(struct folio *folio)\n--\nmm/swapfile.c-2112-/**\nmm/swapfile.c:2113: * swap_put_entries_direct() - Release reference on range of swap entries and\nmm/swapfile.c-2114- *                             reclaim their cache if no more references remain.\n--\nmm/swapfile.c-2124- */\nmm/swapfile.c:2125:void swap_put_entries_direct(swp_entry_t entry, int nr)\nmm/swapfile.c-2126-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 13157
							output: 33
							thoughts: 27
						

Here's my take on the thought process, as requested:

**Navigating `swap_put_entries_direct` and `move_pages_ptes`**

Okay, so I'm looking at `swap_put_entries_direct`. It's not a static function, which immediately tells me something about its scope and potential use cases within the kernel. I need to understand what's calling it and why it's structured this way, the non-static nature definitely suggests it's being accessed from multiple points. This likely implies a degree of shared functionality or perhaps a less tightly scoped responsibility than a static function.

Now, where was I? Right, I should take a look at `move_pages_ptes`. This is probably where the real meat of the operation is. I'm guessing this function is central to moving pages, and `swap_put_entries_direct` is somehow part of that. I'll need to trace the flow between the two to understand the interaction. Is `swap_put_entries_direct` responsible for updating page tables or some sort of swap structure during a page move initiated by `move_pages_ptes`? Understanding that relationship is key.

{
  "Expression": "move_pages_ptes",
  "PathPrefix": "mm/userfaultfd.c"
}

{
  "Output": "mm/userfaultfd.c=1461=static int move_zeropage_pte(struct mm_struct *mm,\n--\nmm/userfaultfd.c-1500- */\nmm/userfaultfd.c:1501:static long move_pages_ptes(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,\nmm/userfaultfd.c-1502-\t\t\t    struct vm_area_struct *dst_vma,\n--\nmm/userfaultfd.c=2021=static ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,\n--\nmm/userfaultfd.c-2155-\nmm/userfaultfd.c:2156:\t\t\tret = move_pages_ptes(mm, dst_pmd, src_pmd,\nmm/userfaultfd.c-2157-\t\t\t\t\t      dst_vma, src_vma, dst_addr,\n"
}

gemini-3.1-pro-preview

null

null

							input: 13730
							output: 30
							thoughts: 31
						

Okay, here's my interpretation of those thoughts, framed as my own mental processing as an expert in the field:

**Internal Reflection on Page Table Management**

Alright, let's break this down. We're thinking about page table manipulation, specifically the "moving" of pages. The fact that `move_pages_ptes` is *static* immediately tells me we're likely dealing with a lower-level, internal helper function, not something directly exposed as a system call or a widely used API. It's probably responsible for handling the fine-grained details of updating page table entries (PTEs) – probably at the hardware level – during a page move operation. It's likely involved in updating the PTEs in both the source and destination page tables.

Then we have `move_pages`, also *static*. That reinforces the idea that we're within the kernel's implementation. It's the core of the page move functionality. This suggests it is a crucial but probably not user-facing operation.

Finally, the mention of `mcopy_atomic` or something *similar* as the actual entry point or the function that ultimately initiates the move. That tells me this is the primary atomic operation. It is most likely where the user, or other core kernel components, initiate the page migration from one location to another. Perhaps, it would handle synchronization and atomicity to ensure data integrity during a potentially complex operation like moving physical pages between different zones or NUMA nodes. This would be the "front door" of the move operation.

{
  "Expression": "move_pages",
  "PathPrefix": "mm/userfaultfd.c"
}

{
  "Output": "mm/userfaultfd.c=1461=static int move_zeropage_pte(struct mm_struct *mm,\n--\nmm/userfaultfd.c-1500- */\nmm/userfaultfd.c:1501:static long move_pages_ptes(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,\nmm/userfaultfd.c-1502-\t\t\t    struct vm_area_struct *dst_vma,\n--\nmm/userfaultfd.c=1946=static void uffd_move_unlock(struct vm_area_struct *dst_vma,\n--\nmm/userfaultfd.c-1954-/**\nmm/userfaultfd.c:1955: * move_pages - move arbitrary anonymous pages of an existing vma\nmm/userfaultfd.c-1956- * @ctx: pointer to the userfaultfd context\n--\nmm/userfaultfd.c-1963- *\nmm/userfaultfd.c:1964: * move_pages() remaps arbitrary anonymous pages atomically in zero\nmm/userfaultfd.c-1965- * copy. It only works on non shared anonymous pages because those can\n--\nmm/userfaultfd.c-1975- * storage or any other I/O device (MADV_DONTFORK in the source vma\nmm/userfaultfd.c:1976: * avoids move_pages() to fail with -EBUSY if the process forks before\nmm/userfaultfd.c:1977: * move_pages() is called), then it will call move_pages() to map the\nmm/userfaultfd.c-1978- * page in the faulting address in the destination vma.\n--\nmm/userfaultfd.c-1992- * the destination virtual memory range is not a whole unmapped hole,\nmm/userfaultfd.c:1993: * move_pages() will fail respectively with -ENOENT or -EEXIST. This\nmm/userfaultfd.c-1994- * provides a very strict behavior to avoid any chance of memory\n--\nmm/userfaultfd.c-1997- * time for any given faulting address. This means that if two threads\nmm/userfaultfd.c:1998: * try to both call move_pages() on the same destination address at the\nmm/userfaultfd.c-1999- * same time, the second thread will get an explicit error from this\n--\nmm/userfaultfd.c-2007- * an amount of bytes successfully moved. If the retval reports a\nmm/userfaultfd.c:2008: * \"short\" remap, the move_pages() command should be repeated by\nmm/userfaultfd.c-2009- * userland with src+retval, dst+reval, len-retval if it wants to know\n--\nmm/userfaultfd.c-2020- */\nmm/userfaultfd.c:2021:static ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,\nmm/userfaultfd.c-2022-\t\t   unsigned long src_start, unsigned long len, __u64 mode)\n--\nmm/userfaultfd.c-2101-\t\t * be strict. If dst_pmd changes into TPH after this check, the\nmm/userfaultfd.c:2102:\t\t * move_pages_huge_pmd() will detect the change and retry\nmm/userfaultfd.c:2103:\t\t * while move_pages_pte() will detect the change and fail.\nmm/userfaultfd.c-2104-\t\t */\n--\nmm/userfaultfd.c-2128-\t\t\t\tsplit_huge_pmd(src_vma, src_pmd, src_addr);\nmm/userfaultfd.c:2129:\t\t\t\t/* The folio will be split by move_pages_pte() */\nmm/userfaultfd.c-2130-\t\t\t\tcontinue;\n--\nmm/userfaultfd.c-2132-\nmm/userfaultfd.c:2133:\t\t\terr = move_pages_huge_pmd(mm, dst_pmd, src_pmd,\nmm/userfaultfd.c-2134-\t\t\t\t\t\t  dst_pmdval, dst_vma, src_vma,\n--\nmm/userfaultfd.c-2155-\nmm/userfaultfd.c:2156:\t\t\tret = move_pages_ptes(mm, dst_pmd, src_pmd,\nmm/userfaultfd.c-2157-\t\t\t\t\t      dst_vma, src_vma, dst_addr,\n--\nmm/userfaultfd.c=4564=static int userfaultfd_move(struct userfaultfd_ctx *ctx,\n--\nmm/userfaultfd.c-4603-\tif (mmget_not_zero(mm)) {\nmm/userfaultfd.c:4604:\t\tret = move_pages(ctx, uffdio_move.dst, uffdio_move.src,\nmm/userfaultfd.c-4605-\t\t\t\t uffdio_move.len, uffdio_move.mode);\n"
}

gemini-3.1-pro-preview

null

null

							input: 15414
							output: 32
							thoughts: 99
						

**Analyzing the Userfaultfd API Entry Point**

Okay, so I'm looking at this `userfaultfd` code, and something's bugging me. Specifically, I see that `userfaultfd_move` is marked as `static`, but it's being called from an `ioctl` operation. Hmm, that's a bit unusual. The `ioctl` entry point is `userfaultfd_ioctl`, of course. But is `userfaultfd_move` the right choice to be internal? Let me re-check that the call path is appropriate.

The documentation is quite clear: it prefers non-static, non-inlined API entrypoints over internal static helper functions. This makes sense from a maintainability and interface perspective. So the real question is, is `userfaultfd_ioctl` the non-static function here? Time to double-check my understanding, it seems like the right one.

no matches

{
  "Expression": "userfaultfd_ioctl",
  "PathPrefix": "fs/userfaultfd.c"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 15753
							output: 25
							thoughts: 61
						

Here's my thought process, distilled:

**Navigating the Userfaultfd Source**

Okay, so I'm trying to locate the `userfaultfd_ioctl` implementation. I seem to recall it being within the `mm/userfaultfd.c` file. Wait, I'm second-guessing myself. Wasn't the old path something like `fs/userfaultfd.c`? Crap, need to verify this... let's check both `mm/userfaultfd.c` and `fs/userfaultfd.c` to be sure. I can't waste time on a wild goose chase.

{
  "Expression": "userfaultfd_ioctl",
  "PathPrefix": ""
}

{
  "Output": "mm/khugepaged.c=2160=static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)\n--\nmm/khugepaged.c-2216-\t\t * userfaultfd_wp() vmas.  But since the mmap_lock is not held,\nmm/khugepaged.c:2217:\t\t * it is still possible for a racing userfaultfd_ioctl() or\nmm/khugepaged.c-2218-\t\t * madvise() to have inserted ptes or markers.  Now that we hold\n--\nmm/userfaultfd.c=4634=static int userfaultfd_api(struct userfaultfd_ctx *ctx,\n--\nmm/userfaultfd.c-4691-\nmm/userfaultfd.c:4692:static long userfaultfd_ioctl(struct file *file, unsigned cmd,\nmm/userfaultfd.c-4693-\t\t\t      unsigned long arg)\n--\nmm/userfaultfd.c=4770=static const struct file_operations userfaultfd_fops = {\n--\nmm/userfaultfd.c-4776-\t.read_iter\t= userfaultfd_read_iter,\nmm/userfaultfd.c:4777:\t.unlocked_ioctl = userfaultfd_ioctl,\nmm/userfaultfd.c-4778-\t.compat_ioctl\t= compat_ptr_ioctl,\n"
}

gemini-3.1-pro-preview

null

null

							input: 16343
							output: 29
							thoughts: 20
						

Here's a summary of my thoughts, presented as if I were the one thinking them:

**Internal Reflection on `userfaultfd`**

Okay, so I'm looking at `userfaultfd_ioctl` here. It's marked as `static`, which immediately tells me a few things about its scope and how it's used within the broader kernel context. That, combined with the name, strongly suggests it's a helper function or an internal detail used to implement the `userfaultfd` mechanism. No surprises there. The crucial part is how it's called, and that's directly tied to the system call itself. Right, the actual system call is `sys_userfaultfd`. So, `userfaultfd_ioctl` likely gets invoked *within* the handler for the `sys_userfaultfd` syscall to perform some of the low-level operations. Now, I need to figure out what those operations are...

{
  "Expression": "SYSCALL_DEFINE.*userfaultfd",
  "PathPrefix": ""
}

{
  "Output": "mm/userfaultfd.c=4831=static inline bool userfaultfd_syscall_allowed(int flags)\n--\nmm/userfaultfd.c-4847-\nmm/userfaultfd.c:4848:SYSCALL_DEFINE1(userfaultfd, int, flags)\nmm/userfaultfd.c-4849-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 16689
							output: 33
							thoughts: 26
						

Here's my thought process, as if I were considering those points:

**Analyzing the Kernel's Interaction with Userfaultfd and Zswap**

Okay, so `sys_userfaultfd` is the critical system call, the entry point we're concerned with. That's the gatekeeper. Now, I need to see how data flows from a user fault into the system. The next logical step is to check `zswap_writeback_entry`. It's likely involved in how the zswap (compressed swap) mechanism handles those userfaultfd-related page faults. Is `zswap_writeback_entry` responsible for actually writing the data that the user faulted on *back* to zswap? Or is it more involved in the initial interception and queuing of the data when a page fault occurs for memory backed by zswap? Either way, its interaction with `userfaultfd` is crucial to understand to see the complete picture. I need to trace the code path here. I expect that these functions may be key to the performance of zswap when userfaultfd is involved.

{
  "Expression": "zswap_writeback_entry",
  "PathPrefix": "mm/zswap.c"
}

{
  "Output": "mm/zswap.c=924=static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio)\n--\nmm/zswap.c-986- */\nmm/zswap.c:987:static int zswap_writeback_entry(struct zswap_entry *entry,\nmm/zswap.c-988-\t\t\t\t swp_entry_t swpentry)\n--\nmm/zswap.c=1090=static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,\n--\nmm/zswap.c-1113-\t * 1. We extract the swp_entry_t to the stack, allowing\nmm/zswap.c:1114:\t *    zswap_writeback_entry() to pin the swap entry and\nmm/zswap.c-1115-\t *    then validate the zswap entry against that swap entry's\n--\nmm/zswap.c-1148-\nmm/zswap.c:1149:\twriteback_result = zswap_writeback_entry(entry, swpentry);\nmm/zswap.c-1150-\n"
}

gemini-3.1-pro-preview

null

null

							input: 17287
							output: 32
							thoughts: 23
						

Here's a summary of my thoughts, tailored for an expert audience:

**Analyzing the Memory Management Interaction**

Okay, so I'm looking at `zswap_writeback_entry`. It's defined as a static variable. The critical part here is understanding *why* it's static and what that implies in terms of scope and potential concurrency issues. It's likely intended to be module-local. It's important to remember that it is static because if it wasn't, multiple instances of the struct could exist, and that would be chaos.

And, of course, the caller is `shrink_memcg_cb`. That's the key. Knowing that ties this specific `zswap` structure directly into the memory cgroup shrinking callback. I'm immediately thinking about the implications for memory reclaim, page eviction, and the overall interaction between `zswap` and the memory cgroup hierarchy. Specifically, the relationship between these two pieces of infrastructure and the performance of the system as a result. I'll need to dig deeper into the code paths that lead from `shrink_memcg_cb` to `zswap_writeback_entry`, and that's likely where the interesting logic resides.

{
  "Expression": "shrink_memcg_cb",
  "PathPrefix": "mm/zswap.c"
}

{
  "Output": "mm/zswap.c=987=static int zswap_writeback_entry(struct zswap_entry *entry,\n--\nmm/zswap.c-1089- */\nmm/zswap.c:1090:static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,\nmm/zswap.c-1091-\t\t\t\t       void *arg)\n--\nmm/zswap.c=1171=static unsigned long zswap_shrinker_scan(struct shrinker *shrinker,\n--\nmm/zswap.c-1182-\nmm/zswap.c:1183:\tshrink_ret = list_lru_shrink_walk(\u0026zswap_list_lru, sc, \u0026shrink_memcg_cb,\nmm/zswap.c-1184-\t\t\u0026encountered_page_in_swapcache);\n--\nmm/zswap.c=1280=static int shrink_memcg(struct mem_cgroup *memcg)\n--\nmm/zswap.c-1297-\t\tshrunk += list_lru_walk_one(\u0026zswap_list_lru, nid, memcg,\nmm/zswap.c:1298:\t\t\t\t\t    \u0026shrink_memcg_cb, NULL, \u0026nr_to_walk);\nmm/zswap.c-1299-\t\tscanned += 1 - nr_to_walk;\n"
}

gemini-3.1-pro-preview

null

null

							input: 17964
							output: 39
							thoughts: 80
						

Here's my summary, as though I'm thinking through this process:

**Zswap Shrinking and Frontswap Investigation**

Okay, so I'm trying to trace how memory is being shrunk within zswap, and I remember that `zswap_shrinker_scan` and `shrink_memcg` are static functions, which is not what I am looking for. Let's see... what are the *non*-static entry points I should be looking at? My initial thought was maybe `zswap_frontswap_store` or `zswap_frontswap_load` if zswap still used frontswap. Wait, no, zswap doesn't use frontswap anymore, right? Right. Okay, scratch that.

Alright, I need to check the non-static functions within `mm/zswap.c`. Time to dive in there and see what jumps out. I am going to see what code is not static and figure out the entrypoints and call chains! Let's get to it.

{
  "Expression": "^[a-z_A-Z0-9]+\\(",
  "PathPrefix": "mm/zswap.c"
}

{
  "Output": "mm/zswap.c=93=static const struct kernel_param_ops zswap_enabled_param_ops = {\n--\nmm/zswap.c-96-};\nmm/zswap.c:97:module_param_cb(enabled, \u0026zswap_enabled_param_ops, \u0026zswap_enabled, 0644);\nmm/zswap.c-98-\n--\nmm/zswap.c=103=static const struct kernel_param_ops zswap_compressor_param_ops = {\n--\nmm/zswap.c-107-};\nmm/zswap.c:108:module_param_cb(compressor, \u0026zswap_compressor_param_ops,\nmm/zswap.c-109-\t\t\u0026zswap_compressor, 0644);\n--\nmm/zswap.c=112=static unsigned int zswap_max_pool_percent = 20;\nmm/zswap.c:113:module_param_named(max_pool_percent, zswap_max_pool_percent, uint, 0644);\nmm/zswap.c-114-\n--\nmm/zswap.c=116=static unsigned int zswap_accept_thr_percent = 90; /* of max pool size */\nmm/zswap.c:117:module_param_named(accept_threshold_percent, zswap_accept_thr_percent,\nmm/zswap.c-118-\t\t   uint, 0644);\n--\nmm/zswap.c=121=static bool zswap_shrinker_enabled = IS_ENABLED(\nmm/zswap.c-122-\t\tCONFIG_ZSWAP_SHRINKER_DEFAULT_ON);\nmm/zswap.c:123:module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);\nmm/zswap.c-124-\n--\nmm/zswap.c=1696=static int debugfs_get_total_size(void *data, u64 *val)\n--\nmm/zswap.c-1700-}\nmm/zswap.c:1701:DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, \"%llu\\n\");\nmm/zswap.c-1702-\nmm/zswap.c=1703=static int debugfs_get_stored_pages(void *data, u64 *val)\n--\nmm/zswap.c-1707-}\nmm/zswap.c:1708:DEFINE_DEBUGFS_ATTRIBUTE(stored_pages_fops, debugfs_get_stored_pages, NULL, \"%llu\\n\");\nmm/zswap.c-1709-\nmm/zswap.c=1710=static int debugfs_get_stored_incompressible_pages(void *data, u64 *val)\n--\nmm/zswap.c-1714-}\nmm/zswap.c:1715:DEFINE_DEBUGFS_ATTRIBUTE(stored_incompressible_pages_fops,\nmm/zswap.c-1716-\t\tdebugfs_get_stored_incompressible_pages, NULL, \"%llu\\n\");\n--\nmm/zswap.c=1824=static int __init zswap_init(void)\n--\nmm/zswap.c-1830-/* must be late so crypto has time to come up */\nmm/zswap.c:1831:late_initcall(zswap_init);\nmm/zswap.c-1832-\nmm/zswap.c:1833:MODULE_AUTHOR(\"Seth Jennings \u003csjennings@variantweb.net\u003e\");\nmm/zswap.c:1834:MODULE_DESCRIPTION(\"Compressed cache for swap pages\");\n"
}

gemini-3.1-pro-preview

null

null

							input: 19259
							output: 64
							thoughts: 22
						

Okay, here's my summary, tailored as if I'm an expert in the field thinking aloud:

**Refining My Search Strategy**

Alright, hang on a second. Before I get too deep into this, I need to be more precise with my search terms. I'm looking for a pattern, a specific language construct, and simply searching generally might lead me down a rabbit hole. I need to be more surgical. I should really be searching for specific return types. That's it! Instead of a broad net, let's try something more targeted. Let's start by looking for function definitions where the return type is explicitly stated. I'm thinking... I need to consider all the common ones, like `void`, of course. Then `int`, `bool`, `float`, and `double` are all very standard. Okay, I'll need to account for more complex types, but let's start with those basics. I'll construct a search pattern that accounts for the possibility of these return types. I'll use a regex perhaps, something that accounts for the start of a line ( `^`) followed by the return type. Then, I can expand as I discover new patterns. I'm on the right track now!

{
  "Expression": "^(void|int|bool|struct [a-z_A-Z0-9]+ \\*)[ \\t]+[a-z_A-Z0-9]+\\(",
  "PathPrefix": "mm/zswap.c"
}

{
  "Output": "mm/zswap.c=123=module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);\nmm/zswap.c-124-\nmm/zswap.c:125:bool zswap_is_enabled(void)\nmm/zswap.c-126-{\n--\nmm/zswap.c-129-\nmm/zswap.c:130:bool zswap_never_enabled(void)\nmm/zswap.c-131-{\n--\nmm/zswap.c=691=static void zswap_lru_del(struct zswap_entry *entry)\n--\nmm/zswap.c-702-\nmm/zswap.c:703:void zswap_lruvec_state_init(struct lruvec *lruvec)\nmm/zswap.c-704-{\n--\nmm/zswap.c-707-\nmm/zswap.c:708:void zswap_folio_swapin(struct folio *folio)\nmm/zswap.c-709-{\n--\nmm/zswap.c-729- */\nmm/zswap.c:730:void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg)\nmm/zswap.c-731-{\n--\nmm/zswap.c=1398=static bool zswap_store_page(struct page *page,\n--\nmm/zswap.c-1477-\nmm/zswap.c:1478:bool zswap_store(struct folio *folio)\nmm/zswap.c-1479-{\n--\nmm/zswap.c-1583- */\nmm/zswap.c:1584:int zswap_load(struct folio *folio)\nmm/zswap.c-1585-{\n--\nmm/zswap.c-1636-\nmm/zswap.c:1637:void zswap_invalidate(swp_entry_t swp)\nmm/zswap.c-1638-{\n--\nmm/zswap.c-1650-\nmm/zswap.c:1651:int zswap_swapon(int type, unsigned long nr_pages)\nmm/zswap.c-1652-{\n--\nmm/zswap.c-1670-\nmm/zswap.c:1671:void zswap_swapoff(int type)\nmm/zswap.c-1672-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 20252
							output: 57
							thoughts: 280
						

**My Focus List: Refining the Approach**

Okay, so I'm thinking about how to best characterize these key functions. `zswap_store` and `zswap_load` seem like the obvious entry points for zswap. However, I need to keep in mind that the writeback is actually triggered by the shrinker. Hmm... I could add both `zswap_store` and `zswap_load` to the focus list, or maybe just `zswap_store`? Actually, wait a minute, I see `zswap_writeback_entry` is *also* called from the shrinker, and `zswap_store` is the function called when storing to swap, so for clarity, I will stick with the `zswap_store` and `zswap_load` pair.

Now, let's go back and re-evaluate this current list:
- `sys_mincore`
- `shmem_get_folio`
- `read_swap_cache_async`
- `swapin_readahead`
- `swap_retry_table_alloc`
- `swp_swapcount`
- `swap_put_entries_direct`
- `sys_userfaultfd`
- `zswap_store`

Ah, right. I just noticed that `sys_mincore` and `sys_userfaultfd` are *syscalls*. I need to be more precise about the functions themselves. Let's see about finding a better one for userfaultfd... `userfaultfd_ioctl` is static, which is usually not a good choice, and is probably not what I'm looking for. Let me check the userfaultfd code, `mm/userfaultfd.c`, for any non-static alternatives. Perhaps `mcopy_atomic` might be relevant, it's worth checking out. I need to make sure I identify functions that are accessible across the system and that represent the behavior I'm interested in capturing.

{
  "Expression": "^(void|int|bool|ssize_t|long)[ \\t]+[a-z_A-Z0-9]+\\(",
  "PathPrefix": "mm/userfaultfd.c"
}

{
  "Output": "mm/userfaultfd.c=90=static __always_inline\nmm/userfaultfd.c:91:bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end)\nmm/userfaultfd.c-92-{\n--\nmm/userfaultfd.c=1068=static ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start,\n--\nmm/userfaultfd.c-1074-\nmm/userfaultfd.c:1075:long uffd_wp_range(struct vm_area_struct *dst_vma,\nmm/userfaultfd.c-1076-\t\t   unsigned long start, unsigned long len, bool enable_wp)\n--\nmm/userfaultfd.c=1104=static int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,\n--\nmm/userfaultfd.c-1166-\nmm/userfaultfd.c:1167:int mrwprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,\nmm/userfaultfd.c-1168-\t\t     unsigned long len, bool enable_rwp)\n--\nmm/userfaultfd.c-1236-\nmm/userfaultfd.c:1237:void double_pt_lock(spinlock_t *ptl1,\nmm/userfaultfd.c-1238-\t\t    spinlock_t *ptl2)\n--\nmm/userfaultfd.c-1251-\nmm/userfaultfd.c:1252:void double_pt_unlock(spinlock_t *ptl1,\nmm/userfaultfd.c-1253-\t\t      spinlock_t *ptl2)\n--\nmm/userfaultfd.c=1827=static __always_inline\nmm/userfaultfd.c:1828:int find_vmas_mm_locked(struct mm_struct *mm,\nmm/userfaultfd.c-1829-\t\t\tunsigned long dst_start,\n--\nmm/userfaultfd.c=2510=static bool userfaultfd_rwp_async_ctx(struct userfaultfd_ctx *ctx)\n--\nmm/userfaultfd.c-2519- */\nmm/userfaultfd.c:2520:bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)\nmm/userfaultfd.c-2521-{\n--\nmm/userfaultfd.c=3091=static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,\n--\nmm/userfaultfd.c-3098-\nmm/userfaultfd.c:3099:int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)\nmm/userfaultfd.c-3100-{\n--\nmm/userfaultfd.c=3152=static void dup_fctx(struct userfaultfd_fork_ctx *fctx)\n--\nmm/userfaultfd.c-3164-\nmm/userfaultfd.c:3165:void dup_userfaultfd_complete(struct list_head *fcs)\nmm/userfaultfd.c-3166-{\n--\nmm/userfaultfd.c-3175-\nmm/userfaultfd.c:3176:void dup_userfaultfd_fail(struct list_head *fcs)\nmm/userfaultfd.c-3177-{\n--\nmm/userfaultfd.c-3203-\nmm/userfaultfd.c:3204:void mremap_userfaultfd_prep(struct vm_area_struct *vma,\nmm/userfaultfd.c-3205-\t\t\t     struct vm_userfaultfd_ctx *vm_ctx)\n--\nmm/userfaultfd.c-3225-\nmm/userfaultfd.c:3226:void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,\nmm/userfaultfd.c-3227-\t\t\t\t unsigned long from, unsigned long to,\n--\nmm/userfaultfd.c-3245-\nmm/userfaultfd.c:3246:void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx)\nmm/userfaultfd.c-3247-{\n--\nmm/userfaultfd.c-3257-\nmm/userfaultfd.c:3258:bool userfaultfd_remove(struct vm_area_struct *vma,\nmm/userfaultfd.c-3259-\t\t\tunsigned long start, unsigned long end)\n--\nmm/userfaultfd.c=3286=static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,\n--\nmm/userfaultfd.c-3298-\nmm/userfaultfd.c:3299:int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start,\nmm/userfaultfd.c-3300-\t\t\t   unsigned long end, struct list_head *unmaps)\n--\nmm/userfaultfd.c-3324-\nmm/userfaultfd.c:3325:void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)\nmm/userfaultfd.c-3326-{\n--\nmm/userfaultfd.c=4488=static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg)\n--\nmm/userfaultfd.c-4544-\nmm/userfaultfd.c:4545:bool userfaultfd_wp_async(struct vm_area_struct *vma)\nmm/userfaultfd.c-4546-{\n--\nmm/userfaultfd.c-4549-\nmm/userfaultfd.c:4550:bool userfaultfd_rwp_async(struct vm_area_struct *vma)\nmm/userfaultfd.c-4551-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 22551
							output: 31
							thoughts: 30
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, presented in the first person:

**Navigating the Userfaultfd Landscape**

Hmm, so `mcopy_atomic` is actually *inside* `mm/userfaultfd.c`? That's a bit unexpected; I thought that module was primarily focused on... well, userfaultfd handling. Okay, let's see. My mental map placed it elsewhere, but it's clearly relevant. I need to understand its relationship to the broader userfaultfd implementation. Time to check `mfill_atomic` as well. I'm guessing that the name association may provide important implementation details. I need to consider both functions in context, probably examining the surrounding code to determine how `mcopy_atomic` and `mfill_atomic` interact, and what specific scenarios trigger their usage. Perhaps there's an optimization being performed here, or a crucial atomic operation tied to page population under userfaultfd. Gotta dig deeper...

{
  "Expression": "mfill_atomic",
  "PathPrefix": "mm/userfaultfd.c"
}

{
  "Output": "mm/userfaultfd.c=336=static bool mfill_file_over_size(struct vm_area_struct *dst_vma,\n--\nmm/userfaultfd.c-356- */\nmm/userfaultfd.c:357:static int mfill_atomic_install_pte(pmd_t *dst_pmd,\nmm/userfaultfd.c-358-\t\t\t\t    struct vm_area_struct *dst_vma,\n--\nmm/userfaultfd.c=525=static int mfill_copy_folio_retry(struct mfill_state *mfill_state,\n--\nmm/userfaultfd.c-561-\nmm/userfaultfd.c:562:static int __mfill_atomic_pte(struct mfill_state *state,\nmm/userfaultfd.c-563-\t\t\t      const struct vm_uffd_ops *ops)\n--\nmm/userfaultfd.c-612-\nmm/userfaultfd.c:613:\tret = mfill_atomic_install_pte(state-\u003epmd, state-\u003evma, dst_addr,\nmm/userfaultfd.c-614-\t\t\t\t       \u0026folio-\u003epage, flags);\n--\nmm/userfaultfd.c-627-\nmm/userfaultfd.c:628:static int mfill_atomic_pte_copy(struct mfill_state *state)\nmm/userfaultfd.c-629-{\n--\nmm/userfaultfd.c-643-\nmm/userfaultfd.c:644:\treturn __mfill_atomic_pte(state, ops);\nmm/userfaultfd.c-645-}\nmm/userfaultfd.c-646-\nmm/userfaultfd.c:647:static int mfill_atomic_pte_zeroed_folio(struct mfill_state *state)\nmm/userfaultfd.c-648-{\n--\nmm/userfaultfd.c-650-\nmm/userfaultfd.c:651:\treturn __mfill_atomic_pte(state, ops);\nmm/userfaultfd.c-652-}\nmm/userfaultfd.c-653-\nmm/userfaultfd.c:654:static int mfill_atomic_pte_zeropage(struct mfill_state *state)\nmm/userfaultfd.c-655-{\n--\nmm/userfaultfd.c-664-\t    (dst_vma-\u003evm_flags \u0026 VM_SHARED))\nmm/userfaultfd.c:665:\t\treturn mfill_atomic_pte_zeroed_folio(state);\nmm/userfaultfd.c-666-\n--\nmm/userfaultfd.c-690-/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */\nmm/userfaultfd.c:691:static int mfill_atomic_pte_continue(struct mfill_state *state)\nmm/userfaultfd.c-692-{\n--\nmm/userfaultfd.c-719-\nmm/userfaultfd.c:720:\tret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,\nmm/userfaultfd.c-721-\t\t\t\t       page, flags);\n--\nmm/userfaultfd.c-733-/* Handles UFFDIO_POISON for all non-hugetlb VMAs. */\nmm/userfaultfd.c:734:static int mfill_atomic_pte_poison(struct mfill_state *state)\nmm/userfaultfd.c-735-{\n--\nmm/userfaultfd.c-772-/*\nmm/userfaultfd.c:773: * mfill_atomic processing for HUGETLB vmas.  Note that this routine is\nmm/userfaultfd.c-774- * called with either vma-lock or mmap_lock held, it will release the lock\n--\nmm/userfaultfd.c-776- */\nmm/userfaultfd.c:777:static __always_inline ssize_t mfill_atomic_hugetlb(\nmm/userfaultfd.c-778-\t\t\t\t\t      struct userfaultfd_ctx *ctx,\n--\nmm/userfaultfd.c-885-\nmm/userfaultfd.c:886:\t\terr = hugetlb_mfill_atomic_pte(dst_pte, dst_vma, dst_addr,\nmm/userfaultfd.c-887-\t\t\t\t\t       src_addr, flags, \u0026folio);\n--\nmm/userfaultfd.c-936-/* fail at build time if gcc attempts to use this */\nmm/userfaultfd.c:937:extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx,\nmm/userfaultfd.c-938-\t\t\t\t    struct vm_area_struct *dst_vma,\n--\nmm/userfaultfd.c-944-\nmm/userfaultfd.c:945:static __always_inline ssize_t mfill_atomic_pte(struct mfill_state *state)\nmm/userfaultfd.c-946-{\n--\nmm/userfaultfd.c-949-\tif (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))\nmm/userfaultfd.c:950:\t\treturn mfill_atomic_pte_continue(state);\nmm/userfaultfd.c-951-\tif (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON))\nmm/userfaultfd.c:952:\t\treturn mfill_atomic_pte_poison(state);\nmm/userfaultfd.c-953-\tif (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY))\nmm/userfaultfd.c:954:\t\treturn mfill_atomic_pte_copy(state);\nmm/userfaultfd.c-955-\tif (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE))\nmm/userfaultfd.c:956:\t\treturn mfill_atomic_pte_zeropage(state);\nmm/userfaultfd.c-957-\n--\nmm/userfaultfd.c-961-\nmm/userfaultfd.c:962:static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,\nmm/userfaultfd.c-963-\t\t\t\t\t    unsigned long dst_start,\n--\nmm/userfaultfd.c-997-\tif (is_vm_hugetlb_page(state.vma))\nmm/userfaultfd.c:998:\t\treturn  mfill_atomic_hugetlb(ctx, state.vma, dst_start,\nmm/userfaultfd.c-999-\t\t\t\t\t     src_start, len, flags);\n--\nmm/userfaultfd.c-1012-\nmm/userfaultfd.c:1013:\t\terr = mfill_atomic_pte(\u0026state);\nmm/userfaultfd.c-1014-\t\tcond_resched();\n--\nmm/userfaultfd.c-1035-\nmm/userfaultfd.c:1036:static ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start,\nmm/userfaultfd.c-1037-\t\t\t  unsigned long src_start, unsigned long len,\n--\nmm/userfaultfd.c-1039-{\nmm/userfaultfd.c:1040:\treturn mfill_atomic(ctx, dst_start, src_start, len,\nmm/userfaultfd.c-1041-\t\t\t    uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY));\n--\nmm/userfaultfd.c-1043-\nmm/userfaultfd.c:1044:static ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx,\nmm/userfaultfd.c-1045-\t\t\t      unsigned long start,\n--\nmm/userfaultfd.c-1047-{\nmm/userfaultfd.c:1048:\treturn mfill_atomic(ctx, start, 0, len,\nmm/userfaultfd.c-1049-\t\t\t    uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE));\n--\nmm/userfaultfd.c-1051-\nmm/userfaultfd.c:1052:static ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start,\nmm/userfaultfd.c-1053-\t\t\t      unsigned long len, uffd_flags_t flags)\n--\nmm/userfaultfd.c-1063-\nmm/userfaultfd.c:1064:\treturn mfill_atomic(ctx, start, 0, len,\nmm/userfaultfd.c-1065-\t\t\t    uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE));\n--\nmm/userfaultfd.c-1067-\nmm/userfaultfd.c:1068:static ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start,\nmm/userfaultfd.c-1069-\t\t\t    unsigned long len, uffd_flags_t flags)\nmm/userfaultfd.c-1070-{\nmm/userfaultfd.c:1071:\treturn mfill_atomic(ctx, start, 0, len,\nmm/userfaultfd.c-1072-\t\t\t    uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON));\n--\nmm/userfaultfd.c=4109=static int userfaultfd_copy(struct userfaultfd_ctx *ctx,\n--\nmm/userfaultfd.c-4146-\tif (mmget_not_zero(ctx-\u003emm)) {\nmm/userfaultfd.c:4147:\t\tret = mfill_atomic_copy(ctx, uffdio_copy.dst, uffdio_copy.src,\nmm/userfaultfd.c-4148-\t\t\t\t\tuffdio_copy.len, flags);\n--\nmm/userfaultfd.c=4169=static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,\n--\nmm/userfaultfd.c-4200-\tif (mmget_not_zero(ctx-\u003emm)) {\nmm/userfaultfd.c:4201:\t\tret = mfill_atomic_zeropage(ctx, uffdio_zeropage.range.start,\nmm/userfaultfd.c-4202-\t\t\t\t\t    uffdio_zeropage.range.len);\n--\nmm/userfaultfd.c=4427=static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)\n--\nmm/userfaultfd.c-4462-\tif (mmget_not_zero(ctx-\u003emm)) {\nmm/userfaultfd.c:4463:\t\tret = mfill_atomic_continue(ctx, uffdio_continue.range.start,\nmm/userfaultfd.c-4464-\t\t\t\t\t    uffdio_continue.range.len, flags);\n--\nmm/userfaultfd.c=4488=static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg)\n--\nmm/userfaultfd.c-4519-\tif (mmget_not_zero(ctx-\u003emm)) {\nmm/userfaultfd.c:4520:\t\tret = mfill_atomic_poison(ctx, uffdio_poison.range.start,\nmm/userfaultfd.c-4521-\t\t\t\t\t  uffdio_poison.range.len, 0);\n"
}

gemini-3.1-pro-preview

null

null

							input: 25776
							output: 27
							thoughts: 79
						

Okay, here's my take on those thoughts, framed from my own perspective:

**Reviewing Memory Configurations for a Patch**

Right, so `sys_userfaultfd` should be okay. No immediate red flags there. Now, let's step through the relevant kernel configs: I need to ensure the system is correctly set up to handle the changes this patch will bring. I'm going to look specifically at how memory is handled.

First, I'll check the `SWAP` configuration – making sure swap space is enabled or disabled as required by this system. After that I'll look at `ZSWAP` and its status. Obviously, `USERFAULTFD` is key here, I need to make certain it is included as well, or at least is correctly set in my target system. I'll include `SHMEM` if it seems necessary. It's usually enabled or defaults to enabled, but better safe than sorry.

Wait a second… the patch touches `mm/shmem.c`. That means I *must* verify `CONFIG_SHMEM` is enabled. It's crucial for understanding the impact of these changes on shared memory. I need to know if this patch relies on or affects shared memory configurations. I can't proceed without that information.

no matches

{
  "Expression": "config SHMEM",
  "PathPrefix": "mm/Kconfig"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 26166
							output: 27
							thoughts: 10
						

Here's my take on the thought process, as if it were my own:

**Diving into the Kernel Configuration Landscape**

Okay, so we need to figure out where this particular configuration option lives. My first instinct, as always, is to go straight to the heart of the kernel's configuration system. Let's see... the `init/` directory feels like the right place to start, given its role in the initialization process. And within that, `Kconfig` is the obvious target. That's where all the configuration options are declared, and hopefully, our mystery option is defined there, along with all the metadata we need. This is the place to start drilling down into the dependencies and descriptions. Let's see what we can find.

{
  "Expression": "config SHMEM",
  "PathPrefix": "init/Kconfig"
}

{
  "Output": "init/Kconfig=1924=config EVENTFD\n--\ninit/Kconfig-1932-\ninit/Kconfig:1933:config SHMEM\ninit/Kconfig-1934-\tbool \"Use full shmem filesystem\" if EXPERT\n"
}

gemini-3.1-pro-preview

null

null

							input: 26437
							output: 34
							thoughts: 200
						

**Kernel Memory Management - Key Considerations**

Okay, so we're talking about shared memory, so `CONFIG_SHMEM` is definitely relevant. Let's see... we've got some kernel configs to keep in mind, specifically `SWAP`, `ZSWAP`, `USERFAULTFD`, and of course, `SHMEM`. Those all play into this.

Now, which symbols are the core of this discussion? We need to keep an eye on `sys_mincore`, `shmem_get_folio`, `read_swap_cache_async`, `swapin_readahead`, `swap_retry_table_alloc`, `swp_swapcount`, `swap_put_entries_direct`, `sys_userfaultfd`, `zswap_store`, and `zswap_load`. Each of these are essential pieces of the puzzle.

Wait a second, how is `sys_mincore` actually defined? Is it simply `sys_mincore` or could it be the x64 specific version, `__x64_sys_mincore`? Syscalls are usually defined using `SYSCALL_DEFINE`, so, let's verify. I could probably get away with just searching for `sys_mincore` or simply `mincore`. Let's just double check in `mm/mincore.c` for any definitions using `SYSCALL_DEFINE`. I'll confirm how it's defined and how it's being used.

{
  "Expression": "SYSCALL_DEFINE.*mincore",
  "PathPrefix": "mm/mincore.c"
}

{
  "Output": "mm/mincore.c=246=static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)\n--\nmm/mincore.c-291- */\nmm/mincore.c:292:SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,\nmm/mincore.c-293-\t\tunsigned char __user *, vec)\n"
}

gemini-3.1-pro-preview

null

null

							input: 27097
							output: 263
							thoughts: 1130
						

**Fuzzing Target Selection: A Kernel Perspective**

Okay, so I'm thinking about how to effectively fuzz this patch. My immediate thought was to leverage `do_mincore`, but then I remembered it's static. That's a no-go since the instructions say to prioritize non-static entry points to avoid inlining issues.  So, I'll go with `sys_mincore` and `sys_userfaultfd` directly. They are syscalls, which Syzkaller should handle easily.

I've got to double-check that the other functions are non-static as well. Let's see... `zswap_store` and `zswap_load` are good.  `read_swap_cache_async`, `swapin_readahead`, `swap_retry_table_alloc`, `swp_swapcount`, `swap_put_entries_direct`, and `shmem_get_folio` all look solid too. Good, good, they're all non-static.

Now, I was a bit hung up on `do_swap_page`. It's definitely a hot path, the main function modified. The patch actually changes how it handles the `VM_FAULT_SIGBUS` return. But, the instructions say to avoid hot-path functions to prevent skewed test distributions. It's a key function in swap, but maybe I can exclude it.  The modified `get_swap_device` is called by all these functions I've listed, so fuzzing those should still hit the relevant logic, particularly the `ERR_PTR(-EINVAL)` handling in `get_swap_device`. I will rely on the other functions to hit that `get_swap_device` behavior. That will give good coverage of the changes.

So, let's review: the patch is about `get_swap_device()` now returning `ERR_PTR(-EINVAL)` instead of `NULL` for bad swap entries. It updates many callers in the kernel to use `IS_ERR_OR_NULL()`, and `do_swap_page` now uses `IS_ERR()` to return `VM_FAULT_SIGBUS`. This fixes a possible infinite loop from malformed entries, so it's a functional, user-reachable change that *needs* fuzzing.

I'll be using configs `SWAP`, `ZSWAP`, `USERFAULTFD`, and `SHMEM` to cover all the relevant subsystems.

My final list of symbols to focus on is: `sys_mincore`, `sys_userfaultfd`, `shmem_get_folio`, `read_swap_cache_async`, `swapin_readahead`, `swap_retry_table_alloc`, `swp_swapcount`, `swap_put_entries_direct`, `zswap_store`, and `zswap_load`.  I feel confident that this selection will provide comprehensive coverage of the patch's changes.

{
  "EnableConfigs": [
    "SWAP",
    "ZSWAP",
    "USERFAULTFD",
    "SHMEM"
  ],
  "FocusSymbols": [
    "shmem_get_folio",
    "read_swap_cache_async",
    "swapin_readahead",
    "swap_retry_table_alloc",
    "swp_swapcount",
    "swap_put_entries_direct",
    "zswap_store",
    "zswap_load"
  ],
  "Reasoning": "The patch modifies `get_swap_device()` to return `ERR_PTR(-EINVAL)` instead of `NULL` for malformed swap entries. It updates multiple callers across memory management subsystems (core mm, shmem, mincore, swapfile, userfaultfd, zswap) to handle the new return type using `IS_ERR_OR_NULL()`. Notably, `do_swap_page()` now explicitly checks for `IS_ERR()` and returns `VM_FAULT_SIGBUS` instead of retrying, fixing a potential infinite page fault loop for malformed entries. This is a functional change in core kernel logic that is reachable from userspace and should be fuzzed.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "SWAP",
    "ZSWAP",
    "USERFAULTFD",
    "SHMEM"
  ],
  "FocusSymbols": [
    "shmem_get_folio",
    "read_swap_cache_async",
    "swapin_readahead",
    "swap_retry_table_alloc",
    "swp_swapcount",
    "swap_put_entries_direct",
    "zswap_store",
    "zswap_load"
  ],
  "Reasoning": "The patch modifies `get_swap_device()` to return `ERR_PTR(-EINVAL)` instead of `NULL` for malformed swap entries. It updates multiple callers across memory management subsystems (core mm, shmem, mincore, swapfile, userfaultfd, zswap) to handle the new return type using `IS_ERR_OR_NULL()`. Notably, `do_swap_page()` now explicitly checks for `IS_ERR()` and returns `VM_FAULT_SIGBUS` instead of retrying, fixing a potential infinite page fault loop for malformed entries. This is a functional change in core kernel logic that is reachable from userspace and should be fuzzed.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

best-expensive

null

{
  "KMSANReasoning": "The patch updates the error handling of `get_swap_device()` to return an error pointer (`ERR_PTR(-EINVAL)`) for malformed swap entries, rather than just `NULL`. It updates various callers in the memory management subsystem (`mm/memory.c`, `mm/mincore.c`, `mm/shmem.c`, `mm/swap_state.c`, `mm/swapfile.c`, `mm/userfaultfd.c`, `mm/zswap.c`) to use `IS_ERR_OR_NULL()` and handle the error appropriately (e.g., returning `VM_FAULT_SIGBUS` in `do_swap_page()`). These changes address logic bugs and potential invalid memory accesses (which are well-covered by KASAN and standard kernel testing). There are no new data structures introduced, no modifications to user-space copy operations, and no changes that would expose uninitialized stack or heap memory. Therefore, KMSAN is not required.",
  "NeedsKMSAN": false
}

You are an expert Linux kernel security engineer specializing in kernel memory
error detectors (KASAN and KMSAN). Your job is to review the provided patch series and
determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer)
fuzzing session in addition to standard KASAN fuzzing.

CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN:
- Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable
  a comprehensive suite of debugging tools and sanitizers, including KASAN
  (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP
  (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks.
- KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap,
  or page allocations) and kernel-to-user memory info-leaks.

Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN,
LOCKDEP, OR OTHER STANDARD BUG DETECTORS.
A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY
set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks
that are detected ONLY by KMSAN.

Look holistically at the patch series and surrounding code. Even if no direct
uninitialized field accesses or new buffer allocations are added in the diff itself,
a patch may alter control flow, bounds checking, or data length calculations in ways
that change how the rest of the code operates on existing buffers (e.g. allowing
uninitialized stack/heap memory to be read, copied to user space, or used in control
flow). Do not hesitate to use your code access tools to inspect the surrounding code,
called functions, and callers.

Set NeedsKMSAN=true ONLY IF the patch introduces or modifies:
1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb
   attributes, ioctl output arguments, socket options, or BPF buffers) where fields
   or structure padding might not be fully initialized/zeroed.
2. Conditional logic or branching that depends on potentially uninitialized variables
   or struct fields.
3. Allocation or initialization of complex data structures where uninitialized fields
   could be read later in reachable code paths.
4. Bounds checks, lengths, or logic in a way that allows surrounding code to access
   uninitialized bytes of existing buffers.

Set NeedsKMSAN=false IF:
- The code changes primarily risk out-of-bounds access, array overflows, NULL pointer
  dereferences, locking deadlocks, or use-after-free bugs (these are already caught
  by KASAN, LOCKDEP, or standard bug detectors).
- All stack/heap structures touched or introduced by the patch are fully zeroed
  or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied.
- The patch does not introduce any risk of uninitialized memory usage or info-leaks.

Use your code access tools to inspect the surrounding code if necessary, then provide
detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 457f6d75f8d75a6177b9fb967997a8c5d1a677e5
Author: syz-cluster <triage@syzkaller.com>
Date:   Mon Aug 10 19:38:21 2026 +0000

    syz-cluster: applied patch under review

diff --git a/mm/memory.c b/mm/memory.c
index d9cf941967cf0..2842cd976f1d3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4956,8 +4956,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 	/* Prevent swapoff from happening to us. */
 	si = get_swap_device(entry);
-	if (unlikely(!si))
+	if (IS_ERR_OR_NULL(si)) {
+		/* A malformed entry never becomes valid, so don't retry it. */
+		if (IS_ERR(si))
+			ret = VM_FAULT_SIGBUS;
+		si = NULL;
 		goto out;
+	}
 
 	folio = swap_cache_get_folio(entry);
 	if (folio)
diff --git a/mm/mincore.c b/mm/mincore.c
index ff4ac82817683..c086836bc4bcc 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -71,7 +71,7 @@ static unsigned char mincore_swap(swp_entry_t entry, bool shmem)
 	 */
 	if (shmem) {
 		si = get_swap_device(entry);
-		if (!si)
+		if (IS_ERR_OR_NULL(si))
 			return 0;
 	}
 	folio = swap_cache_get_folio(entry);
diff --git a/mm/shmem.c b/mm/shmem.c
index 65572cbf1bd3c..d0a9f52bfed71 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2276,7 +2276,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 
 	si = get_swap_device(index_entry);
 	order = shmem_confirm_swap(mapping, index, index_entry);
-	if (unlikely(!si)) {
+	if (IS_ERR_OR_NULL(si)) {
 		if (order < 0)
 			return -EEXIST;
 		else
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 4b7a3303c463b..f2e86d6626ecc 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -715,7 +715,7 @@ struct folio *read_swap_cache_async(struct swap_io_ctx *ctx, swp_entry_t entry,
 	struct folio *folio;
 
 	si = get_swap_device(entry);
-	if (!si)
+	if (IS_ERR_OR_NULL(si))
 		return NULL;
 
 	mpol = get_vma_policy(vma, addr, 0, &ilx);
@@ -951,7 +951,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 		 */
 		if (swp_type(entry) != swp_type(targ_entry)) {
 			si = get_swap_device(entry);
-			if (!si)
+			if (IS_ERR_OR_NULL(si))
 				continue;
 		}
 		folio = swap_cache_read_folio(&ctx, entry, gfp_mask, mpol, ilx,
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4d4e3e3059f6b..29612a0cf7afa 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1504,7 +1504,7 @@ int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp)
 	unsigned long offset = swp_offset(entry);
 
 	si = get_swap_device(entry);
-	if (!si)
+	if (IS_ERR_OR_NULL(si))
 		return 0;
 
 	ci = __swap_offset_to_cluster(si, offset);
@@ -1859,7 +1859,9 @@ void folio_put_swap(struct folio *folio, struct page *page)
  * Check whether swap entry is valid in the swap device.  If so,
  * return pointer to swap_info_struct, and keep the swap entry valid
  * via preventing the swap device from being swapoff, until
- * put_swap_device() is called.  Otherwise return NULL.
+ * put_swap_device() is called.  Return NULL for an empty entry or a
+ * device that is going away, and ERR_PTR(-EINVAL) if the entry itself
+ * is malformed and can never name a slot on any device.
  *
  * Notice that swapoff or swapoff+swapon can still happen before the
  * percpu_ref_tryget_live() in get_swap_device() or after the
@@ -1899,13 +1901,14 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)
 
 	return si;
 bad_nofile:
-	pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_file, entry.val);
+	return ERR_PTR(-EINVAL);
 out:
 	return NULL;
 put_out:
-	pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
 	percpu_ref_put(&si->users);
-	return NULL;
+	return ERR_PTR(-EINVAL);
 }
 
 /*
@@ -2001,7 +2004,7 @@ int swp_swapcount(swp_entry_t entry)
 	int count;
 
 	si = get_swap_device(entry);
-	if (!si)
+	if (IS_ERR_OR_NULL(si))
 		return 0;
 
 	ci = swap_cluster_lock(si, swp_offset(entry));
@@ -2127,7 +2130,7 @@ void swap_put_entries_direct(swp_entry_t entry, int nr)
 	struct swap_info_struct *si;
 
 	si = get_swap_device(entry);
-	if (WARN_ON_ONCE(!si))
+	if (WARN_ON_ONCE(IS_ERR_OR_NULL(si)))
 		return;
 	if (WARN_ON_ONCE(end_offset > si->max))
 		goto out;
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 24a4d92ffa3c2..bf7bc7fb1aa0f 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1700,7 +1700,8 @@ static long move_pages_ptes(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd
 		}
 
 		si = get_swap_device(entry);
-		if (unlikely(!si)) {
+		if (IS_ERR_OR_NULL(si)) {
+			si = NULL;
 			ret = -EAGAIN;
 			goto out;
 		}
diff --git a/mm/zswap.c b/mm/zswap.c
index f7c9c89f6449c..bc9b931d6f447 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -997,7 +997,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 
 	/* try to allocate swap cache folio */
 	si = get_swap_device(swpentry);
-	if (!si)
+	if (IS_ERR_OR_NULL(si))
 		return -EEXIST;
 
 	mpol = get_task_policy(current);

gemini-3.1-pro-preview

null

null

							input: 3999
							output: 234
							thoughts: 475
						

**KMSAN Assessment: Swap Entry Error Handling Patch**

Okay, let's take a look at this patch. It's focused on improving the error handling in `get_swap_device()`. Specifically, instead of returning `NULL` for certain errors with swap entries (like bad files or offsets), the function now returns an error pointer, `ERR_PTR(-EINVAL)`. The subsequent change is updating the callers of `get_swap_device()` to use `IS_ERR_OR_NULL()` for the check, instead of simply `!si`. This pattern is seen throughout the `mm` subsystem, affecting a range of files. In `do_swap_page()`, a critical function, if `IS_ERR(si)` is true, it triggers `VM_FAULT_SIGBUS`.

My understanding is that this patch is entirely about robustifying the kernel's response to *malformed* or *invalid* swap entries. It's a logic and memory safety improvement. The issue at hand is likely related to out-of-bounds reads or writes, resulting in crashes or infinite loops. This kind of problem is exactly the sort of thing that KASAN and standard kernel testing are designed to detect.

The key question is always: does this patch introduce any *new* uninitialized memory exposure? I think not. `get_swap_device()` returns a pointer to a `struct swap_info_struct`, which is then checked by callers. There's no scenario here where uninitialized memory is being directly exposed. No new data structures are introduced, no user-space copies are modified, and I see no risk of uninitialized stack or heap memory being exposed through this change.

Therefore, after a careful review, I'm confident in setting `NeedsKMSAN=false`. This is about better error handling and preventing crashes from bad swap entries, not about exposing KMSAN-relevant issues.

{
  "KMSANReasoning": "The patch updates the error handling of `get_swap_device()` to return an error pointer (`ERR_PTR(-EINVAL)`) for malformed swap entries, rather than just `NULL`. It updates various callers in the memory management subsystem (`mm/memory.c`, `mm/mincore.c`, `mm/shmem.c`, `mm/swap_state.c`, `mm/swapfile.c`, `mm/userfaultfd.c`, `mm/zswap.c`) to use `IS_ERR_OR_NULL()` and handle the error appropriately (e.g., returning `VM_FAULT_SIGBUS` in `do_swap_page()`). These changes address logic bugs and potential invalid memory accesses (which are well-covered by KASAN and standard kernel testing). There are no new data structures introduced, no modifications to user-space copy operations, and no changes that would expose uninitialized stack or heap memory. Therefore, KMSAN is not required.",
  "NeedsKMSAN": false
}

{
  "KMSANReasoning": "The patch updates the error handling of `get_swap_device()` to return an error pointer (`ERR_PTR(-EINVAL)`) for malformed swap entries, rather than just `NULL`. It updates various callers in the memory management subsystem (`mm/memory.c`, `mm/mincore.c`, `mm/shmem.c`, `mm/swap_state.c`, `mm/swapfile.c`, `mm/userfaultfd.c`, `mm/zswap.c`) to use `IS_ERR_OR_NULL()` and handle the error appropriately (e.g., returning `VM_FAULT_SIGBUS` in `do_swap_page()`). These changes address logic bugs and potential invalid memory accesses (which are well-covered by KASAN and standard kernel testing). There are no new data structures introduced, no modifications to user-space copy operations, and no changes that would expose uninitialized stack or heap memory. Therefore, KMSAN is not required.",
  "NeedsKMSAN": false
}