AI Trajectory

null

{
  "EnableConfigs": [
    "SWAP"
  ],
  "FocusSymbols": [
    "wp_can_reuse_anon_folio",
    "do_swap_page"
  ],
  "Reasoning": "The patch modifies core memory management functions `wp_can_reuse_anon_folio` and `do_swap_page` to change how folio reference counts and LRU cache status are handled during copy-on-write and swap-in page faults. These are functional changes to reachable core kernel logic that affect swap and page fault handling.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 933cf52bb1dd8072ab2ab1d08bca52432135a1a2\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Tue Jun 23 23:41:06 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/mm/memory.c b/mm/memory.c\nindex ff338c2abe9231..14577c67c61a9b 100644\n--- a/mm/memory.c\n+++ b/mm/memory.c\n@@ -4193,12 +4193,18 @@ static bool wp_can_reuse_anon_folio(struct folio *folio,\n \t */\n \tif (folio_test_ksm(folio) || folio_ref_count(folio) \u003e 3)\n \t\treturn false;\n-\tif (!folio_test_lru(folio))\n+\tif (!folio_test_lru(folio)) {\n+\t\t/*\n+\t\t * Assume folio is on lru_cache and holds a cache reference.\n+\t\t */\n+\t\tif (folio_ref_count(folio) \u003e 2 + folio_test_swapcache(folio))\n+\t\t\treturn false;\n \t\t/*\n \t\t * We cannot easily detect+handle references from\n \t\t * remote LRU caches or references to LRU folios.\n \t\t */\n \t\tlru_add_drain();\n+\t}\n \tif (folio_ref_count(folio) \u003e 1 + folio_test_swapcache(folio))\n \t\treturn false;\n \tif (!folio_trylock(folio))\n@@ -4897,16 +4903,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)\n \t} else if (folio != swapcache)\n \t\tpage = folio_page(folio, 0);\n \n-\t/*\n-\t * If we want to map a page that's in the swapcache writable, we\n-\t * have to detect via the refcount if we're really the exclusive\n-\t * owner. Try removing the extra reference from the local LRU\n-\t * caches if required.\n-\t */\n-\tif ((vmf-\u003eflags \u0026 FAULT_FLAG_WRITE) \u0026\u0026\n-\t    !folio_test_ksm(folio) \u0026\u0026 !folio_test_lru(folio))\n-\t\tlru_add_drain();\n-\n \tfolio_throttle_swaprate(folio, GFP_KERNEL);\n \n \t/*\n@@ -5043,12 +5039,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)\n \n \t/*\n \t * Same logic as in do_wp_page(); however, optimize for pages that are\n-\t * certainly not shared either because we just allocated them without\n-\t * exposing them to the swapcache or because the swap entry indicates\n-\t * exclusivity.\n+\t * certainly not because the swap entry indicates exclusivity.\n \t */\n-\tif (!folio_test_ksm(folio) \u0026\u0026\n-\t    (exclusive || folio_ref_count(folio) == 1)) {\n+\tif (!folio_test_ksm(folio) \u0026\u0026 exclusive) {\n \t\tif ((vma-\u003evm_flags \u0026 VM_WRITE) \u0026\u0026 !userfaultfd_pte_wp(vma, pte) \u0026\u0026\n \t\t    !pte_needs_soft_dirty_wp(vma, pte)) {\n \t\t\tpte = pte_mkwrite(pte, vma);\n@@ -5094,8 +5087,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)\n \t * Remove the swap entry and conditionally try to free up the swapcache.\n \t * Do it after mapping, so raced page faults will likely see the folio\n \t * in swap cache and wait on the folio lock.\n+\t * Assume non-LRU folios may be queued in the LRU cache, which contributes\n+\t * an additional reference to the folio.\n \t */\n-\tif (should_try_to_free_swap(si, folio, vma, nr_pages, vmf-\u003eflags))\n+\tif (should_try_to_free_swap(si, folio, vma, nr_pages +\n+\t\t\t!folio_test_lru(folio), vmf-\u003eflags))\n \t\tfolio_free_swap(folio);\n \n \tfolio_unlock(folio);\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "SWAP"
  ],
  "FocusSymbols": [
    "wp_can_reuse_anon_folio",
    "do_swap_page"
  ],
  "Reasoning": "The patch modifies core memory management functions `wp_can_reuse_anon_folio` and `do_swap_page` to change how folio reference counts and LRU cache status are handled during copy-on-write and swap-in page faults. These are functional changes to reachable core kernel logic that affect swap and page fault handling.",
  "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).

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.
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.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. 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 933cf52bb1dd8072ab2ab1d08bca52432135a1a2
Author: syz-cluster <triage@syzkaller.com>
Date:   Tue Jun 23 23:41:06 2026 +0000

    syz-cluster: applied patch under review

diff --git a/mm/memory.c b/mm/memory.c
index ff338c2abe9231..14577c67c61a9b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4193,12 +4193,18 @@ static bool wp_can_reuse_anon_folio(struct folio *folio,
 	 */
 	if (folio_test_ksm(folio) || folio_ref_count(folio) > 3)
 		return false;
-	if (!folio_test_lru(folio))
+	if (!folio_test_lru(folio)) {
+		/*
+		 * Assume folio is on lru_cache and holds a cache reference.
+		 */
+		if (folio_ref_count(folio) > 2 + folio_test_swapcache(folio))
+			return false;
 		/*
 		 * We cannot easily detect+handle references from
 		 * remote LRU caches or references to LRU folios.
 		 */
 		lru_add_drain();
+	}
 	if (folio_ref_count(folio) > 1 + folio_test_swapcache(folio))
 		return false;
 	if (!folio_trylock(folio))
@@ -4897,16 +4903,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	} else if (folio != swapcache)
 		page = folio_page(folio, 0);
 
-	/*
-	 * If we want to map a page that's in the swapcache writable, we
-	 * have to detect via the refcount if we're really the exclusive
-	 * owner. Try removing the extra reference from the local LRU
-	 * caches if required.
-	 */
-	if ((vmf->flags & FAULT_FLAG_WRITE) &&
-	    !folio_test_ksm(folio) && !folio_test_lru(folio))
-		lru_add_drain();
-
 	folio_throttle_swaprate(folio, GFP_KERNEL);
 
 	/*
@@ -5043,12 +5039,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 	/*
 	 * Same logic as in do_wp_page(); however, optimize for pages that are
-	 * certainly not shared either because we just allocated them without
-	 * exposing them to the swapcache or because the swap entry indicates
-	 * exclusivity.
+	 * certainly not because the swap entry indicates exclusivity.
 	 */
-	if (!folio_test_ksm(folio) &&
-	    (exclusive || folio_ref_count(folio) == 1)) {
+	if (!folio_test_ksm(folio) && exclusive) {
 		if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
 		    !pte_needs_soft_dirty_wp(vma, pte)) {
 			pte = pte_mkwrite(pte, vma);
@@ -5094,8 +5087,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	 * Remove the swap entry and conditionally try to free up the swapcache.
 	 * Do it after mapping, so raced page faults will likely see the folio
 	 * in swap cache and wait on the folio lock.
+	 * Assume non-LRU folios may be queued in the LRU cache, which contributes
+	 * an additional reference to the folio.
 	 */
-	if (should_try_to_free_swap(si, folio, vma, nr_pages, vmf->flags))
+	if (should_try_to_free_swap(si, folio, vma, nr_pages +
+			!folio_test_lru(folio), vmf->flags))
 		folio_free_swap(folio);
 
 	folio_unlock(folio);

gemini-3.1-pro-preview

null

null

							input: 2622
							output: 36
							thoughts: 611
						

**Analyzing a Memory Management Patch**

Okay, so I'm looking at this patch for `mm/memory.c`, and it's tweaking some critical functions: `wp_can_reuse_anon_folio` and `do_swap_page`. These are right in the heart of the memory management subsystem, dealing with page faults, swap operations, and copy-on-write. This definitely warrants a closer look, especially from a fuzzing perspective. The modifications seem subtle, but any change here can have far-reaching consequences.

Specifically, `wp_can_reuse_anon_folio` seems to be getting some added logic around reference counting and LRU (Least Recently Used) list management. It looks like they're trying to refine the conditions under which an anonymous folio can be reused. The added `lru_add_drain()` calls suggest an attempt to deal with potential stale references from remote LRU caches. It seems the commit also optimizes a refcount check to determine exclusive ownership. This could have some interesting implications on concurrency or race conditions during page reclaim and swap-out.

In `do_swap_page`, the changes are a bit more focused. There's a removal of an `lru_add_drain()` call. This suggests a optimization; potentially, we don't have to worry about stale LRU references when swapcache folios are writeable. Furthermore, a refcount check condition has been altered for determining exclusivity. Another change relates to `should_try_to_free_swap`, where an additional check is added when a folio isn't on the LRU.

Given that these are core MM functions, I'm thinking about fuzzing this pretty aggressively. I don't see any obvious new configuration dependencies, though `do_swap_page` is probably tied to `CONFIG_SWAP`. It would be a good idea to double-check that `mm/memory.c` has that config active. I should probably have a quick look through the code to make sure there's nothing else subtly affected by these changes. I'll need to pay close attention to the interactions between these functions, the LRU, swap cache, and any potential race conditions involving page faults.

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

{
  "Output": "mm/memory.c=4735=static void check_swap_exclusive(struct folio *folio, swp_entry_t entry,\n--\nmm/memory.c-4752- */\nmm/memory.c:4753:vm_fault_t do_swap_page(struct vm_fault *vmf)\nmm/memory.c-4754-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 3834
							output: 31
							thoughts: 18
						

Okay, let's see...

**Checking for Conditional Compilation of `do_swap_page`**

Right, before I dive too deep into this function's logic, I need to make sure I understand its context. My first step is to quickly verify if `do_swap_page` is wrapped in any `#ifdef` preprocessor directives. I need to know if its behavior is contingent on specific compilation flags or configurations. If it's conditionally compiled, that immediately changes the scope of my analysis. I need to account for those possibilities before I can make any definitive statements about its function. I'm going to look for any `#ifdef`, `#ifndef`, or similar directives around the function declaration or definition. Understanding the compilation context is key before I even start to truly comprehend what this function is designed to do.

no matches

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

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 4066
							output: 35
							thoughts: 47
						

Here's my thought process, as if I were reviewing this code:

**Spot Check on Swap Implementation**

Okay, hold on a minute. I was pretty sure `do_swap_page` was always gated by the `CONFIG_SWAP` macro, but something feels off. It's unusual for swap-related functions to be unconditionally compiled. I need to verify that quickly. Let's jump into `mm/memory.c` and zero in around line 4753. I'm going to look for any inclusion guard or conditional compilation around that function's definition. This is a crucial check because if it's not guarded, it suggests a configuration error or potentially unintended behavior in systems where swap is disabled. I want to rule out a misconfiguration or a missing `#ifdef` directive immediately.

{
  "File": "mm/memory.c",
  "FirstLine": 4700,
  "LineCount": 100
}

{
  "Contents": "4700:\t\torders = thp_swap_suitable_orders(swp_offset(entry),\n4701:\t\t\t\t\t\t  vmf-\u003eaddress, orders);\n4702:\t\n4703:\t\tif (!orders)\n4704:\t\t\treturn 0;\n4705:\t\n4706:\t\tpte = pte_offset_map_lock(vmf-\u003evma-\u003evm_mm, vmf-\u003epmd,\n4707:\t\t\t\t\t  vmf-\u003eaddress \u0026 PMD_MASK, \u0026ptl);\n4708:\t\tif (unlikely(!pte))\n4709:\t\t\treturn 0;\n4710:\t\n4711:\t\t/*\n4712:\t\t * For do_swap_page, find the highest order where the aligned range is\n4713:\t\t * completely swap entries with contiguous swap offsets.\n4714:\t\t */\n4715:\t\torder = highest_order(orders);\n4716:\t\twhile (orders) {\n4717:\t\t\taddr = ALIGN_DOWN(vmf-\u003eaddress, PAGE_SIZE \u003c\u003c order);\n4718:\t\t\tif (can_swapin_thp(vmf, pte + pte_index(addr), 1 \u003c\u003c order))\n4719:\t\t\t\tbreak;\n4720:\t\t\torder = next_order(\u0026orders, order);\n4721:\t\t}\n4722:\t\n4723:\t\tpte_unmap_unlock(pte, ptl);\n4724:\t\n4725:\t\treturn orders;\n4726:\t}\n4727:\t#else /* !CONFIG_TRANSPARENT_HUGEPAGE */\n4728:\tstatic unsigned long thp_swapin_suitable_orders(struct vm_fault *vmf)\n4729:\t{\n4730:\t\treturn 0;\n4731:\t}\n4732:\t#endif /* CONFIG_TRANSPARENT_HUGEPAGE */\n4733:\t\n4734:\t/* Sanity check that a folio is fully exclusive */\n4735:\tstatic void check_swap_exclusive(struct folio *folio, swp_entry_t entry,\n4736:\t\t\t\t\t unsigned int nr_pages)\n4737:\t{\n4738:\t\t/* Called under PT locked and folio locked, the swap count is stable */\n4739:\t\tdo {\n4740:\t\t\tVM_WARN_ON_ONCE_FOLIO(__swap_count(entry) != 1, folio);\n4741:\t\t\tentry.val++;\n4742:\t\t} while (--nr_pages);\n4743:\t}\n4744:\t\n4745:\t/*\n4746:\t * We enter with either the VMA lock or the mmap_lock held (see\n4747:\t * FAULT_FLAG_VMA_LOCK), and pte mapped but not yet locked.\n4748:\t * We return with pte unmapped and unlocked.\n4749:\t *\n4750:\t * When returning, the lock may have been released in the same cases\n4751:\t * as done by filemap_fault().\n4752:\t */\n4753:\tvm_fault_t do_swap_page(struct vm_fault *vmf)\n4754:\t{\n4755:\t\tstruct vm_area_struct *vma = vmf-\u003evma;\n4756:\t\tstruct folio *swapcache = NULL, *folio;\n4757:\t\tstruct page *page;\n4758:\t\tstruct swap_info_struct *si = NULL;\n4759:\t\trmap_t rmap_flags = RMAP_NONE;\n4760:\t\tbool exclusive = false;\n4761:\t\tsoftleaf_t entry;\n4762:\t\tpte_t pte;\n4763:\t\tvm_fault_t ret = 0;\n4764:\t\tint nr_pages;\n4765:\t\tunsigned long page_idx;\n4766:\t\tunsigned long address;\n4767:\t\tpte_t *ptep;\n4768:\t\n4769:\t\tif (!pte_unmap_same(vmf))\n4770:\t\t\tgoto out;\n4771:\t\n4772:\t\tentry = softleaf_from_pte(vmf-\u003eorig_pte);\n4773:\t\tif (unlikely(!softleaf_is_swap(entry))) {\n4774:\t\t\tif (softleaf_is_migration(entry)) {\n4775:\t\t\t\tmigration_entry_wait(vma-\u003evm_mm, vmf-\u003epmd,\n4776:\t\t\t\t\t\t     vmf-\u003eaddress);\n4777:\t\t\t} else if (softleaf_is_device_exclusive(entry)) {\n4778:\t\t\t\tvmf-\u003epage = softleaf_to_page(entry);\n4779:\t\t\t\tret = remove_device_exclusive_entry(vmf);\n4780:\t\t\t} else if (softleaf_is_device_private(entry)) {\n4781:\t\t\t\tif (vmf-\u003eflags \u0026 FAULT_FLAG_VMA_LOCK) {\n4782:\t\t\t\t\t/*\n4783:\t\t\t\t\t * migrate_to_ram is not yet ready to operate\n4784:\t\t\t\t\t * under VMA lock.\n4785:\t\t\t\t\t */\n4786:\t\t\t\t\tvma_end_read(vma);\n4787:\t\t\t\t\tret = VM_FAULT_RETRY;\n4788:\t\t\t\t\tgoto out;\n4789:\t\t\t\t}\n4790:\t\n4791:\t\t\t\tvmf-\u003epage = softleaf_to_page(entry);\n4792:\t\t\t\tvmf-\u003epte = pte_offset_map_lock(vma-\u003evm_mm, vmf-\u003epmd,\n4793:\t\t\t\t\t\tvmf-\u003eaddress, \u0026vmf-\u003eptl);\n4794:\t\t\t\tif (unlikely(!vmf-\u003epte ||\n4795:\t\t\t\t\t     !pte_same(ptep_get(vmf-\u003epte),\n4796:\t\t\t\t\t\t\t\tvmf-\u003eorig_pte)))\n4797:\t\t\t\t\tgoto unlock;\n4798:\t\n4799:\t\t\t\t/*\n"
}

gemini-3.1-pro-preview

null

null

							input: 5876
							output: 37
							thoughts: 98
						

**Fuzzing Focus: Swap Handling in the Kernel**

Okay, so `do_swap_page` is always compiled, which makes it a prime target. It's the go-to function for handling swap entries, and that means it's pretty central to how the kernel manages memory. The core changes I'm interested in revolve around `wp_can_reuse_anon_folio` and, of course, `do_swap_page` itself. These are *fundamental* MM functions, and any vulnerabilities here could have serious consequences.

`wp_can_reuse_anon_folio` looks particularly interesting from a fuzzing perspective, and the same applies to `do_swap_page`. Given the significance of those functions, I should start by diving into `wp_can_reuse_anon_folio` in more detail. That's where I'll focus my initial efforts.

{
  "Expression": "^static bool wp_can_reuse_anon_folio",
  "PathPrefix": "mm/memory.c"
}

{
  "Output": "mm/memory.c=4174=static bool __wp_can_reuse_large_anon_folio(struct folio *folio,\n--\nmm/memory.c-4180-\nmm/memory.c:4181:static bool wp_can_reuse_anon_folio(struct folio *folio,\nmm/memory.c-4182-\t\t\t\t    struct vm_area_struct *vma)\n"
}

gemini-3.1-pro-preview

null

null

							input: 6310
							output: 30
							thoughts: 95
						

**Investigating the Dependency of `do_swap_page` on `CONFIG_SWAP`**

Okay, so I'm thinking about the role of `CONFIG_SWAP` in relation to `do_swap_page`. The core of my question is whether `do_swap_page` can even *do* anything meaningful if swapping is disabled. It's pretty clear that `do_swap_page` is invoked when a page fault occurs on a memory location that corresponds to a swap entry. But if `CONFIG_SWAP` is off, there's no swapping infrastructure. That means no swap entries would be created in the first place, right? So, now I need to figure out exactly what happens in the code. I need to dig in and determine if `do_swap_page` is either compiled out entirely, or if it gracefully returns some kind of error code or handles the situation in another appropriate way when `CONFIG_SWAP` is set to false. Understanding that edge case is important for overall system robustness.

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

{
  "Output": "mm/memory.c=3520=int apply_to_existing_page_range(struct mm_struct *mm, unsigned long addr,\n--\nmm/memory.c-3529- * or configurations (e.g. i386 with PAE) which might give a mix of unmatched\nmm/memory.c:3530: * parts, do_swap_page must check under lock before unmapping the pte and\nmm/memory.c-3531- * proceeding (but do_wp_page is only called after already making such a check;\n--\nmm/memory.c=4667=static unsigned long thp_swapin_suitable_orders(struct vm_fault *vmf)\n--\nmm/memory.c-4711-\t/*\nmm/memory.c:4712:\t * For do_swap_page, find the highest order where the aligned range is\nmm/memory.c-4713-\t * completely swap entries with contiguous swap offsets.\n--\nmm/memory.c=4735=static void check_swap_exclusive(struct folio *folio, swp_entry_t entry,\n--\nmm/memory.c-4752- */\nmm/memory.c:4753:vm_fault_t do_swap_page(struct vm_fault *vmf)\nmm/memory.c-4754-{\n--\nmm/memory.c-5082-\tset_ptes(vma-\u003evm_mm, address, ptep, pte, nr_pages);\nmm/memory.c:5083:\tarch_do_swap_page_nr(vma-\u003evm_mm, vma, address,\nmm/memory.c-5084-\t\t\tpte, pte, nr_pages);\n--\nmm/memory.c=6331=static vm_fault_t handle_pte_fault(struct vm_fault *vmf)\n--\nmm/memory.c-6377-\tif (!pte_present(vmf-\u003eorig_pte))\nmm/memory.c:6378:\t\treturn do_swap_page(vmf);\nmm/memory.c-6379-\n"
}

gemini-3.1-pro-preview

null

null

							input: 7187
							output: 26
							thoughts: 106
						

**Investigating the Role of `do_swap_page` in a Memory Fault Scenario**

Okay, so `do_swap_page` is being called from `handle_pte_fault` if the original page table entry (PTE) isn't present. Makes sense, that's the core swap-in function, right? But hold on a second... my mind just sparked a question: if swap is *disabled*—`CONFIG_SWAP` is set to false—does that function, `do_swap_page`, even exist? I need to check.

Alright, I see it's defined in `mm/memory.c`. Seems like it's there unconditionally, which initially surprised me a bit. However, wait a minute, to have swap entries, I need `CONFIG_SWAP` enabled, right? So, while the function might exist as a declaration, the actual swap-related logic should be conditional on `CONFIG_SWAP`. I should dig deeper and confirm that `CONFIG_SWAP` is indeed a prerequisite for any meaningful `do_swap_page` operation. That seems to be the key point here.

{
  "Expression": "CONFIG_SWAP",
  "PathPrefix": "mm/"
}

{
  "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\n--\nmm/filemap.c=4591=static void filemap_cachestat(struct address_space *mapping,\n--\nmm/filemap.c-4638-\nmm/filemap.c:4639:#ifdef CONFIG_SWAP /* implies CONFIG_MMU */\nmm/filemap.c-4640-\t\t\tif (shmem_mapping(mapping)) {\n--\nmm/ksm.c=3107=struct folio *ksm_might_need_to_copy(struct folio *folio,\n--\nmm/ksm.c-3146-\t\t__folio_set_locked(new_folio);\nmm/ksm.c:3147:#ifdef CONFIG_SWAP\nmm/ksm.c-3148-\t\tcount_vm_event(KSM_SWPIN_COPY);\n--\nmm/madvise.c=150=static int madvise_update_vma(vm_flags_t new_flags,\n--\nmm/madvise.c-185-\nmm/madvise.c:186:#ifdef CONFIG_SWAP\nmm/madvise.c-187-static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,\n--\nmm/madvise.c=234=static void shmem_swapin_range(struct vm_area_struct *vma,\n--\nmm/madvise.c-269-}\nmm/madvise.c:270:#endif\t\t/* CONFIG_SWAP */\nmm/madvise.c-271-\n--\nmm/madvise.c=281=static long madvise_willneed(struct madvise_behavior *madv_behavior)\n--\nmm/madvise.c-289-\nmm/madvise.c:290:#ifdef CONFIG_SWAP\nmm/madvise.c-291-\tif (!file) {\n--\nmm/memcontrol-v1.c=596=void memcg1_commit_charge(struct folio *folio, struct mem_cgroup *memcg)\n--\nmm/memcontrol-v1.c-605-\nmm/memcontrol-v1.c:606:#ifdef CONFIG_SWAP\nmm/memcontrol-v1.c-607-/**\n--\nmm/memcontrol-v1.c=1866=static const unsigned int memcg1_stats[] = {\n--\nmm/memcontrol-v1.c-1877-\tWORKINGSET_REFAULT_FILE,\nmm/memcontrol-v1.c:1878:#ifdef CONFIG_SWAP\nmm/memcontrol-v1.c-1879-\tMEMCG_SWAP,\n--\nmm/memcontrol-v1.c=1884=static const char *const memcg1_stat_names[] = {\n--\nmm/memcontrol-v1.c-1895-\t\"workingset_refault_file\",\nmm/memcontrol-v1.c:1896:#ifdef CONFIG_SWAP\nmm/memcontrol-v1.c-1897-\t\"swap\",\n--\nmm/memcontrol.c=372=static const unsigned int memcg_node_stat_items[] = {\n--\nmm/memcontrol.c-399-\tNR_SECONDARY_PAGETABLE,\nmm/memcontrol.c:400:#ifdef CONFIG_SWAP\nmm/memcontrol.c-401-\tNR_SWAPCACHE,\n--\nmm/memcontrol.c=553=static const unsigned int memcg_vm_event_stat[] = {\n--\nmm/memcontrol.c-565-\tPGLAZYFREED,\nmm/memcontrol.c:566:#ifdef CONFIG_SWAP\nmm/memcontrol.c-567-\tSWPIN_ZERO,\n--\nmm/memcontrol.c=1546=static const struct memory_stat memory_stats[] = {\n--\nmm/memcontrol.c-1564-\t{ \"file_writeback\",\t\tNR_WRITEBACK\t\t\t},\nmm/memcontrol.c:1565:#ifdef CONFIG_SWAP\nmm/memcontrol.c-1566-\t{ \"swapcached\",\t\t\tNR_SWAPCACHE\t\t\t},\n--\nmm/memcontrol.c=5536=int __init mem_cgroup_init(void)\n--\nmm/memcontrol.c-5571-\nmm/memcontrol.c:5572:#ifdef CONFIG_SWAP\nmm/memcontrol.c-5573-/**\n--\nmm/memcontrol.c=6035=subsys_initcall(mem_cgroup_swap_init);\nmm/memcontrol.c-6036-\nmm/memcontrol.c:6037:#endif /* CONFIG_SWAP */\nmm/memcontrol.c-6038-\n--\nmm/migrate.c=571=static int __folio_migrate_mapping(struct address_space *mapping,\n--\nmm/migrate.c-690-\t\t}\nmm/migrate.c:691:#ifdef CONFIG_SWAP\nmm/migrate.c-692-\t\tif (folio_test_swapcache(folio)) {\n--\nmm/mincore.c=61=static unsigned char mincore_swap(swp_entry_t entry, bool shmem)\n--\nmm/mincore.c-74-\nmm/mincore.c:75:\tif (!IS_ENABLED(CONFIG_SWAP)) {\nmm/mincore.c-76-\t\tWARN_ON(1);\n--\nmm/swap.h=69=enum swap_cluster_flags {\n--\nmm/swap.h-80-\nmm/swap.h:81:#ifdef CONFIG_SWAP\nmm/swap.h-82-#include \u003clinux/swapops.h\u003e /* for swp_offset */\n--\nmm/swap.h=332=static inline unsigned int folio_swap_flags(struct folio *folio)\n--\nmm/swap.h-336-\nmm/swap.h:337:#else /* CONFIG_SWAP */\nmm/swap.h-338-struct swap_iocb;\n--\nmm/swap.h=470=static inline unsigned int folio_swap_flags(struct folio *folio)\n--\nmm/swap.h-474-\nmm/swap.h:475:#endif /* CONFIG_SWAP */\nmm/swap.h-476-#endif /* _MM_SWAP_H */\n--\nmm/vma_init.c=41=static void vm_area_init_from(const struct vm_area_struct *src,\n--\nmm/vma_init.c-64-#endif\nmm/vma_init.c:65:#ifdef CONFIG_SWAP\nmm/vma_init.c-66-\tmemcpy(\u0026dest-\u003eswap_readahead_info, \u0026src-\u003eswap_readahead_info,\n--\nmm/vmstat.c=1187=const char * const vmstat_text[] = {\n--\nmm/vmstat.c-1267-#endif\nmm/vmstat.c:1268:#ifdef CONFIG_SWAP\nmm/vmstat.c-1269-\t[I(NR_SWAPCACHE)]\t\t\t= \"nr_swapcached\",\n--\nmm/vmstat.c-1438-\nmm/vmstat.c:1439:#ifdef CONFIG_SWAP\nmm/vmstat.c-1440-\t[I(SWAP_RA)]\t\t\t\t= \"swap_ra\",\n"
}

gemini-3.1-pro-preview

null

null

							input: 9501
							output: 31
							thoughts: 169
						

**Investigating Swap Configuration and its Impact**

Okay, so I'm trying to figure out the interplay between the swap configuration and a particular function, and the location of `do_swap_page` immediately grabbed my attention. I remember that's in `mm/memory.c`. My first thought is, "Is that file even *conditionally* compiled based on `CONFIG_SWAP`?" But then, I mentally step back and realize `mm/memory.c` is always compiled. However, `do_swap_page` is specifically designed to manage swap entries, and those wouldn't even exist if swap is disabled, so `CONFIG_SWAP` would have to be relevant here. Then I thought about testing swap so I immediately thought, `CONFIG_SWAP` has to be enabled for tests.

Alright, let's change gears a bit. I need to look into `wp_can_reuse_anon_folio`. That's also in `mm/memory.c`, so we're still on solid ground. This function is involved in handling anonymous folios. Now, what's interesting is that `wp_can_reuse_anon_folio` calls `folio_test_swapcache(folio)`. Now, *that* call is pretty telling. It's directly interacting with a swap cache, so, yes, `CONFIG_SWAP` is definitely a key factor.

Now, let me investigate the logic involving `should_try_to_free_swap`.

{
  "Expression": "should_try_to_free_swap",
  "PathPrefix": "mm/"
}

{
  "Output": "mm/memory.c=4470=static vm_fault_t remove_device_exclusive_entry(struct vm_fault *vmf)\n--\nmm/memory.c-4517- */\nmm/memory.c:4518:static inline bool should_try_to_free_swap(struct swap_info_struct *si,\nmm/memory.c-4519-\t\t\t\t\t   struct folio *folio,\n--\nmm/memory.c=4753=vm_fault_t do_swap_page(struct vm_fault *vmf)\n--\nmm/memory.c-5092-\t */\nmm/memory.c:5093:\tif (should_try_to_free_swap(si, folio, vma, nr_pages +\nmm/memory.c-5094-\t\t\t!folio_test_lru(folio), vmf-\u003eflags))\n"
}

gemini-3.1-pro-preview

null

null

							input: 10245
							output: 34
							thoughts: 18
						

Okay, let's dive into this. Here's my thought process on what I'm looking at:

**Deconstructing `should_try_to_free_swap`**

Right, so I've been asked to understand the function `should_try_to_free_swap`. My initial thought is, let's break down exactly *what* that function is supposed to be doing. The name itself is fairly descriptive, but I need to understand the specifics of its logic and its place within the larger system. I'll need to figure out the parameters, what conditions trigger a "yes" answer, and what the implications of a "no" are. I need to understand the performance and resource implications of the answer, I bet some of it relies on thresholds and the nature of the system the call is a part of.

{
  "File": "mm/memory.c",
  "FirstLine": 4518,
  "LineCount": 20
}

{
  "Contents": "4518:\tstatic inline bool should_try_to_free_swap(struct swap_info_struct *si,\n4519:\t\t\t\t\t\t   struct folio *folio,\n4520:\t\t\t\t\t\t   struct vm_area_struct *vma,\n4521:\t\t\t\t\t\t   unsigned int extra_refs,\n4522:\t\t\t\t\t\t   unsigned int fault_flags)\n4523:\t{\n4524:\t\tif (!folio_test_swapcache(folio))\n4525:\t\t\treturn false;\n4526:\t\t/*\n4527:\t\t * Always try to free swap cache for SWP_SYNCHRONOUS_IO devices. Swap\n4528:\t\t * cache can help save some IO or memory overhead, but these devices\n4529:\t\t * are fast, and meanwhile, swap cache pinning the slot deferring the\n4530:\t\t * release of metadata or fragmentation is a more critical issue.\n4531:\t\t */\n4532:\t\tif (data_race(si-\u003eflags \u0026 SWP_SYNCHRONOUS_IO))\n4533:\t\t\treturn true;\n4534:\t\tif (mem_cgroup_swap_full(folio) || (vma-\u003evm_flags \u0026 VM_LOCKED) ||\n4535:\t\t    folio_test_mlocked(folio))\n4536:\t\t\treturn true;\n4537:\t\t/*\n"
}

gemini-3.1-pro-preview

null

null

							input: 10821
							output: 123
							thoughts: 1052
						

**Fuzzing Plan: Swap and Copy-on-Write Memory Management**

Okay, so I've got this patch that touches `wp_can_reuse_anon_folio` and `do_swap_page`. These are both deep in the core of memory management, dealing with swapping and copy-on-write functionality. It looks like the changes are functional, which means we *absolutely* need to fuzz this.

Now, the main configuration variable is `CONFIG_SWAP`. The focus symbols, the functions we really want to target with the fuzzer, are those two: `wp_can_reuse_anon_folio` and `do_swap_page`. Wait a minute, `do_swap_page`... isn't that a hot-path function? Yes, it's called on every page fault that hits a swapped-out page. And `wp_can_reuse_anon_folio` is called on every write fault to an anonymous page. Are they too hot to fuzz? Potentially, but they *are* the exact functions that were modified.

Let's check to ensure there aren't any other functions involved. Nope, the patch *only* modifies these two functions. If we don't include them, there aren't any focus symbols. Okay, we'll keep them. Hmm, `wp_can_reuse_anon_folio` is static though. Syzkaller can still fuzz static functions, since coverage is collected from every function.

Let's verify the patch itself:

It looks like the change adds a check for `folio_ref_count(folio) > 2 + folio_test_swapcache(folio)`.
Also, removes a call to `lru_add_drain()`.
And removes a check for `folio_ref_count(folio) == 1`.
Finally, modifies the `extra_refs` argument to `should_try_to_free_swap`.

All these changes are functional. The code affects swap and page fault handling. Definitely worth fuzzing!

So, the plan is:

*   **WorthFuzzing**: True.
*   **FocusSymbols**: `wp_can_reuse_anon_folio`, `do_swap_page`.
*   **EnableConfigs**: `SWAP`.

Alright, I think we're ready to proceed. Let's make sure `SWAP` is the correct config name. Yes, `CONFIG_SWAP`.

Is there any other config?
`CONFIG_MEMCG`? `mem_cgroup_swap_full` is used in `should_try_to_free_swap`.
But `SWAP` is the main one.

Let's call `set-results`.

{
  "EnableConfigs": [
    "SWAP"
  ],
  "FocusSymbols": [
    "wp_can_reuse_anon_folio",
    "do_swap_page"
  ],
  "Reasoning": "The patch modifies core memory management functions `wp_can_reuse_anon_folio` and `do_swap_page` to change how folio reference counts and LRU cache status are handled during copy-on-write and swap-in page faults. These are functional changes to reachable core kernel logic that affect swap and page fault handling.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "SWAP"
  ],
  "FocusSymbols": [
    "wp_can_reuse_anon_folio",
    "do_swap_page"
  ],
  "Reasoning": "The patch modifies core memory management functions `wp_can_reuse_anon_folio` and `do_swap_page` to change how folio reference counts and LRU cache status are handled during copy-on-write and swap-in page faults. These are functional changes to reachable core kernel logic that affect swap and page fault handling.",
  "WorthFuzzing": true
}