AI Trajectory

null

{
  "EnableConfigs": [
    "EXT4_FS"
  ],
  "FocusSymbols": [
    "ext4_ext_map_blocks",
    "ext4_es_cache_extent",
    "ext4_map_query_blocks"
  ],
  "Reasoning": "The patch modifies the ext4 extent status caching logic by introducing a `pre_search` parameter to `ext4_es_cache_extent`. This allows avoiding a write lock if the extent is already cached, optimizing block mapping and querying operations. This is a functional change in the core ext4 filesystem logic and is reachable via standard file operations.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 2370c3798ddec7af21442e39991be23098c2662d\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Sun Jul 26 05:13:45 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/fs/ext4/extents.c b/fs/ext4/extents.c\nindex 91c97af64b3177..85e213761a18d5 100644\n--- a/fs/ext4/extents.c\n+++ b/fs/ext4/extents.c\n@@ -537,12 +537,12 @@ static void ext4_cache_extents(struct inode *inode,\n \n \t\tif (prev \u0026\u0026 (prev != lblk))\n \t\t\text4_es_cache_extent(inode, prev, lblk - prev, ~0,\n-\t\t\t\t\t     EXTENT_STATUS_HOLE);\n+\t\t\t\t\t     EXTENT_STATUS_HOLE, false);\n \n \t\tif (ext4_ext_is_unwritten(ex))\n \t\t\tstatus = EXTENT_STATUS_UNWRITTEN;\n \t\text4_es_cache_extent(inode, lblk, len,\n-\t\t\t\t     ext4_ext_pblock(ex), status);\n+\t\t\t\t     ext4_ext_pblock(ex), status, false);\n \t\tprev = lblk + len;\n \t}\n }\n@@ -4239,7 +4239,8 @@ static ext4_lblk_t ext4_ext_determine_insert_hole(struct inode *inode,\n insert_hole:\n \t/* Put just found gap into cache to speed up subsequent requests */\n \text_debug(inode, \" -\u003e %u:%u\\n\", hole_start, len);\n-\text4_es_cache_extent(inode, hole_start, len, ~0, EXTENT_STATUS_HOLE);\n+\text4_es_cache_extent(inode, hole_start, len, ~0, EXTENT_STATUS_HOLE,\n+\t\t\t     false);\n \n \t/* Update hole_len to reflect hole size after lblk */\n \tif (hole_start != lblk)\n@@ -4310,13 +4311,15 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,\n \t\text4_lblk_t ee_block = le32_to_cpu(ex-\u003eee_block);\n \t\text4_fsblk_t ee_start = ext4_ext_pblock(ex);\n \t\tunsigned short ee_len;\n-\n+\t\tunsigned int status;\n \n \t\t/*\n \t\t * unwritten extents are treated as holes, except that\n \t\t * we split out initialized portions during a write.\n \t\t */\n \t\tee_len = ext4_ext_get_actual_len(ex);\n+\t\tstatus = ext4_ext_is_unwritten(ex) ?\n+\t\t\t EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;\n \n \t\ttrace_ext4_ext_show_extent(inode, ee_block, ee_start, ee_len);\n \n@@ -4328,6 +4331,12 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,\n \t\t\text_debug(inode, \"%u fit into %u:%d -\u003e %llu\\n\",\n \t\t\t\t  map-\u003em_lblk, ee_block, ee_len, newblock);\n \n+\t\t\tif (!(flags \u0026 (EXT4_GET_BLOCKS_CREATE |\n+\t\t\t\t       EXT4_EX_NOCACHE)))\n+\t\t\t\text4_es_cache_extent(inode, ee_block, ee_len,\n+\t\t\t\t\t\t     ee_start, status,\n+\t\t\t\t\t\t     true);\n+\n \t\t\t/*\n \t\t\t * If the extent is initialized check whether the\n \t\t\t * caller wants to convert it to unwritten.\ndiff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c\nindex 6e4a191e821915..5a03878b061602 100644\n--- a/fs/ext4/extents_status.c\n+++ b/fs/ext4/extents_status.c\n@@ -1023,7 +1023,7 @@ void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,\n  */\n void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,\n \t\t\t  ext4_lblk_t len, ext4_fsblk_t pblk,\n-\t\t\t  unsigned int status)\n+\t\t\t  unsigned int status, bool pre_search)\n {\n \tstruct extent_status *es;\n \tstruct extent_status chkes, newes;\n@@ -1043,6 +1043,21 @@ void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,\n \n \tBUG_ON(end \u003c lblk);\n \n+\t/*\n+\t * Avoid taking i_es_lock for writing if the entire extent is already\n+\t * cached. The write-locked search below rechecks after a miss.\n+\t */\n+\tif (pre_search) {\n+\t\tread_lock(\u0026EXT4_I(inode)-\u003ei_es_lock);\n+\t\tes = __es_tree_search(\u0026EXT4_I(inode)-\u003ei_es_tree.root, lblk);\n+\t\tif (es \u0026\u0026 es-\u003ees_lblk \u003c= lblk \u0026\u0026 ext4_es_end(es) \u003e= end \u0026\u0026\n+\t\t    !__es_check_extent_status(es, status, NULL)) {\n+\t\t\tread_unlock(\u0026EXT4_I(inode)-\u003ei_es_lock);\n+\t\t\treturn;\n+\t\t}\n+\t\tread_unlock(\u0026EXT4_I(inode)-\u003ei_es_lock);\n+\t}\n+\n \twrite_lock(\u0026EXT4_I(inode)-\u003ei_es_lock);\n \tes = __es_tree_search(\u0026EXT4_I(inode)-\u003ei_es_tree.root, lblk);\n \tif (es \u0026\u0026 es-\u003ees_lblk \u003c= end) {\ndiff --git a/fs/ext4/extents_status.h b/fs/ext4/extents_status.h\nindex f3396cf32b4464..c2da72e3c82ba7 100644\n--- a/fs/ext4/extents_status.h\n+++ b/fs/ext4/extents_status.h\n@@ -139,7 +139,7 @@ extern void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,\n \t\t\t\t  bool delalloc_reserve_used);\n extern void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,\n \t\t\t\t ext4_lblk_t len, ext4_fsblk_t pblk,\n-\t\t\t\t unsigned int status);\n+\t\t\t\t unsigned int status, bool pre_search);\n extern void ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,\n \t\t\t\t  ext4_lblk_t len);\n extern void ext4_es_find_extent_range(struct inode *inode,\ndiff --git a/fs/ext4/inode.c b/fs/ext4/inode.c\nindex ce99807c5f5b2c..d43266c4897858 100644\n--- a/fs/ext4/inode.c\n+++ b/fs/ext4/inode.c\n@@ -523,7 +523,7 @@ static int ext4_map_query_blocks_next_in_leaf(handle_t *handle,\n \n \tif (retval \u003c= 0) {\n \t\text4_es_cache_extent(inode, map-\u003em_lblk, map-\u003em_len,\n-\t\t\t\t     map-\u003em_pblk, status);\n+\t\t\t\t     map-\u003em_pblk, status, true);\n \t\treturn map-\u003em_len;\n \t}\n \n@@ -546,11 +546,11 @@ static int ext4_map_query_blocks_next_in_leaf(handle_t *handle,\n \t\t\tstatus == status2) {\n \t\text4_es_cache_extent(inode, map-\u003em_lblk,\n \t\t\t\t     map-\u003em_len + map2.m_len, map-\u003em_pblk,\n-\t\t\t\t     status);\n+\t\t\t\t     status, true);\n \t\tmap-\u003em_len += map2.m_len;\n \t} else {\n \t\text4_es_cache_extent(inode, map-\u003em_lblk, map-\u003em_len,\n-\t\t\t\t     map-\u003em_pblk, status);\n+\t\t\t\t     map-\u003em_pblk, status, true);\n \t}\n \n \treturn map-\u003em_len;\n@@ -562,6 +562,13 @@ int ext4_map_query_blocks(handle_t *handle, struct inode *inode,\n \tunsigned int status;\n \tint retval;\n \tunsigned int orig_mlen = map-\u003em_len;\n+\t/*\n+\t * ext4_ext_map_blocks() may have already cached the full extent, so\n+\t * search first to avoid taking i_es_lock for writing. The indirect\n+\t * path does not prepopulate the ES tree after the initial lookup miss.\n+\t */\n+\tbool pre_search = ext4_test_inode_flag(inode,\n+\t\t\t\t\t      EXT4_INODE_EXTENTS);\n \n \tflags \u0026= EXT4_EX_QUERY_FILTER;\n \tif (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))\n@@ -593,7 +600,7 @@ int ext4_map_query_blocks(handle_t *handle, struct inode *inode,\n \t\tstatus = map-\u003em_flags \u0026 EXT4_MAP_UNWRITTEN ?\n \t\t\t\tEXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;\n \t\text4_es_cache_extent(inode, map-\u003em_lblk, map-\u003em_len,\n-\t\t\t\t     map-\u003em_pblk, status);\n+\t\t\t\t     map-\u003em_pblk, status, pre_search);\n \t} else {\n \t\tretval = ext4_map_query_blocks_next_in_leaf(handle, inode, map,\n \t\t\t\t\t\t\t    orig_mlen);\n"
}

best-expensive

null

{
  "EnableConfigs": [
    "EXT4_FS"
  ],
  "FocusSymbols": [
    "ext4_ext_map_blocks",
    "ext4_es_cache_extent",
    "ext4_map_query_blocks"
  ],
  "Reasoning": "The patch modifies the ext4 extent status caching logic by introducing a `pre_search` parameter to `ext4_es_cache_extent`. This allows avoiding a write lock if the extent is already cached, optimizing block mapping and querying operations. This is a functional change in the core ext4 filesystem logic and is reachable via standard file operations.",
  "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 2370c3798ddec7af21442e39991be23098c2662d
Author: syz-cluster <triage@syzkaller.com>
Date:   Sun Jul 26 05:13:45 2026 +0000

    syz-cluster: applied patch under review

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 91c97af64b3177..85e213761a18d5 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -537,12 +537,12 @@ static void ext4_cache_extents(struct inode *inode,
 
 		if (prev && (prev != lblk))
 			ext4_es_cache_extent(inode, prev, lblk - prev, ~0,
-					     EXTENT_STATUS_HOLE);
+					     EXTENT_STATUS_HOLE, false);
 
 		if (ext4_ext_is_unwritten(ex))
 			status = EXTENT_STATUS_UNWRITTEN;
 		ext4_es_cache_extent(inode, lblk, len,
-				     ext4_ext_pblock(ex), status);
+				     ext4_ext_pblock(ex), status, false);
 		prev = lblk + len;
 	}
 }
@@ -4239,7 +4239,8 @@ static ext4_lblk_t ext4_ext_determine_insert_hole(struct inode *inode,
 insert_hole:
 	/* Put just found gap into cache to speed up subsequent requests */
 	ext_debug(inode, " -> %u:%u\n", hole_start, len);
-	ext4_es_cache_extent(inode, hole_start, len, ~0, EXTENT_STATUS_HOLE);
+	ext4_es_cache_extent(inode, hole_start, len, ~0, EXTENT_STATUS_HOLE,
+			     false);
 
 	/* Update hole_len to reflect hole size after lblk */
 	if (hole_start != lblk)
@@ -4310,13 +4311,15 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 		ext4_lblk_t ee_block = le32_to_cpu(ex->ee_block);
 		ext4_fsblk_t ee_start = ext4_ext_pblock(ex);
 		unsigned short ee_len;
-
+		unsigned int status;
 
 		/*
 		 * unwritten extents are treated as holes, except that
 		 * we split out initialized portions during a write.
 		 */
 		ee_len = ext4_ext_get_actual_len(ex);
+		status = ext4_ext_is_unwritten(ex) ?
+			 EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
 
 		trace_ext4_ext_show_extent(inode, ee_block, ee_start, ee_len);
 
@@ -4328,6 +4331,12 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 			ext_debug(inode, "%u fit into %u:%d -> %llu\n",
 				  map->m_lblk, ee_block, ee_len, newblock);
 
+			if (!(flags & (EXT4_GET_BLOCKS_CREATE |
+				       EXT4_EX_NOCACHE)))
+				ext4_es_cache_extent(inode, ee_block, ee_len,
+						     ee_start, status,
+						     true);
+
 			/*
 			 * If the extent is initialized check whether the
 			 * caller wants to convert it to unwritten.
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 6e4a191e821915..5a03878b061602 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -1023,7 +1023,7 @@ void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
  */
 void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
 			  ext4_lblk_t len, ext4_fsblk_t pblk,
-			  unsigned int status)
+			  unsigned int status, bool pre_search)
 {
 	struct extent_status *es;
 	struct extent_status chkes, newes;
@@ -1043,6 +1043,21 @@ void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
 
 	BUG_ON(end < lblk);
 
+	/*
+	 * Avoid taking i_es_lock for writing if the entire extent is already
+	 * cached. The write-locked search below rechecks after a miss.
+	 */
+	if (pre_search) {
+		read_lock(&EXT4_I(inode)->i_es_lock);
+		es = __es_tree_search(&EXT4_I(inode)->i_es_tree.root, lblk);
+		if (es && es->es_lblk <= lblk && ext4_es_end(es) >= end &&
+		    !__es_check_extent_status(es, status, NULL)) {
+			read_unlock(&EXT4_I(inode)->i_es_lock);
+			return;
+		}
+		read_unlock(&EXT4_I(inode)->i_es_lock);
+	}
+
 	write_lock(&EXT4_I(inode)->i_es_lock);
 	es = __es_tree_search(&EXT4_I(inode)->i_es_tree.root, lblk);
 	if (es && es->es_lblk <= end) {
diff --git a/fs/ext4/extents_status.h b/fs/ext4/extents_status.h
index f3396cf32b4464..c2da72e3c82ba7 100644
--- a/fs/ext4/extents_status.h
+++ b/fs/ext4/extents_status.h
@@ -139,7 +139,7 @@ extern void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
 				  bool delalloc_reserve_used);
 extern void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
 				 ext4_lblk_t len, ext4_fsblk_t pblk,
-				 unsigned int status);
+				 unsigned int status, bool pre_search);
 extern void ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
 				  ext4_lblk_t len);
 extern void ext4_es_find_extent_range(struct inode *inode,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ce99807c5f5b2c..d43266c4897858 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -523,7 +523,7 @@ static int ext4_map_query_blocks_next_in_leaf(handle_t *handle,
 
 	if (retval <= 0) {
 		ext4_es_cache_extent(inode, map->m_lblk, map->m_len,
-				     map->m_pblk, status);
+				     map->m_pblk, status, true);
 		return map->m_len;
 	}
 
@@ -546,11 +546,11 @@ static int ext4_map_query_blocks_next_in_leaf(handle_t *handle,
 			status == status2) {
 		ext4_es_cache_extent(inode, map->m_lblk,
 				     map->m_len + map2.m_len, map->m_pblk,
-				     status);
+				     status, true);
 		map->m_len += map2.m_len;
 	} else {
 		ext4_es_cache_extent(inode, map->m_lblk, map->m_len,
-				     map->m_pblk, status);
+				     map->m_pblk, status, true);
 	}
 
 	return map->m_len;
@@ -562,6 +562,13 @@ int ext4_map_query_blocks(handle_t *handle, struct inode *inode,
 	unsigned int status;
 	int retval;
 	unsigned int orig_mlen = map->m_len;
+	/*
+	 * ext4_ext_map_blocks() may have already cached the full extent, so
+	 * search first to avoid taking i_es_lock for writing. The indirect
+	 * path does not prepopulate the ES tree after the initial lookup miss.
+	 */
+	bool pre_search = ext4_test_inode_flag(inode,
+					      EXT4_INODE_EXTENTS);
 
 	flags &= EXT4_EX_QUERY_FILTER;
 	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
@@ -593,7 +600,7 @@ int ext4_map_query_blocks(handle_t *handle, struct inode *inode,
 		status = map->m_flags & EXT4_MAP_UNWRITTEN ?
 				EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
 		ext4_es_cache_extent(inode, map->m_lblk, map->m_len,
-				     map->m_pblk, status);
+				     map->m_pblk, status, pre_search);
 	} else {
 		retval = ext4_map_query_blocks_next_in_leaf(handle, inode, map,
 							    orig_mlen);

gemini-3.1-pro-preview

null

null

							input: 4384
							output: 32
							thoughts: 473
						

**Analyzing the Impact of the ext4 Extent Caching Patch**

Okay, so I'm looking at this patch for the ext4 filesystem, and it looks like we're dealing with a change that modifies `fs/ext4/extents.c`, `fs/ext4/extents_status.c`, `fs/ext4/extents_status.h`, and `fs/ext4/inode.c`. The core of the change revolves around adding a `bool pre_search` parameter to the `ext4_es_cache_extent` function. Essentially, if this `pre_search` flag is set to true, it means the code will perform a read lock and search of the extent before taking the write lock. This seems like a pretty targeted optimization to the extent caching strategy, aiming to prevent unnecessary write lock contention if the extent is already cached.

Digging deeper, the patch also modifies `ext4_ext_map_blocks` to call `ext4_es_cache_extent` with `pre_search = true` under specific conditions. This is a functional change, definitely impacting core ext4 logic. The stated goal of the patch is to optimize extent caching by circumventing the write lock if the extent is already cached. I need to keep in mind that this is touching reachable core kernel logic related to the ext4 filesystem.

Now, let's pinpoint the key functions we need to focus on for fuzzing. From my initial assessment, the modified functions are: `ext4_cache_extents`, `ext4_ext_determine_insert_hole`, `ext4_ext_map_blocks`, `ext4_es_cache_extent`, `ext4_map_query_blocks_next_in_leaf`, and `ext4_map_query_blocks`.

To focus our fuzzing efforts most efficiently, I need to know which of those functions are exported. `ext4_es_cache_extent` is exported, as is `ext4_ext_map_blocks` and `ext4_map_query_blocks`. However, `ext4_cache_extents`, `ext4_ext_determine_insert_hole`, and `ext4_map_query_blocks_next_in_leaf` are static, so I can probably de-prioritize those, as it would be more challenging to target them directly in isolation.

So, the clear targets for fuzzing become:
*   `ext4_ext_map_blocks`
*   `ext4_es_cache_extent`
*   `ext4_map_query_blocks`

Finally, let's make sure there aren't any special kernel configurations I need to be aware of. I need to double-check `fs/ext4/Kconfig` for any dependencies. I know `EXT4_FS` is the main one, but a quick `grep` will be the best way to verify there are no hidden requirements.

{
  "Expression": "config EXT4_FS",
  "PathPrefix": "fs/ext4/Kconfig"
}

{
  "Output": "fs/ext4/Kconfig-1-# SPDX-License-Identifier: GPL-2.0-only\nfs/ext4/Kconfig:2:config EXT4_FS\nfs/ext4/Kconfig-3-\ttristate \"The Extended 4 (ext4) filesystem\"\n--\nfs/ext4/Kconfig=35=config EXT4_USE_FOR_EXT2\n--\nfs/ext4/Kconfig-45-\nfs/ext4/Kconfig:46:config EXT4_FS_POSIX_ACL\nfs/ext4/Kconfig-47-\tbool \"Ext4 POSIX Access Control Lists\"\n--\nfs/ext4/Kconfig-55-\nfs/ext4/Kconfig:56:config EXT4_FS_SECURITY\nfs/ext4/Kconfig-57-\tbool \"Ext4 Security Labels\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 5732
							output: 33
							thoughts: 126
						

**Analyzing EXT4 Filesystem Configuration and Potential Fuzzing Targets**

Okay, so the base filesystem configuration is definitely `EXT4_FS`. No need to complicate things, we'll keep it simple and just use `EXT4_FS`.

Now, I want to identify some good areas for fuzzing within the EXT4 codebase. Let's see... `ext4_ext_map_blocks` looks like a prime candidate. It's called during block mapping, which is a core function, so it's probably executed frequently. That makes it a solid target for fuzzer coverage, particularly focusing on how it handles extents. I have a hunch that edge cases in extent mapping are a fertile ground for discovering vulnerabilities.

`ext4_es_cache_extent` is another interesting one, I'll definitely keep an eye on that one.

And, of course, `ext4_map_query_blocks`, given its role in FIEMAP and related queries, has to be checked as well.

To better understand the call graph, I'm going to look at the callers of `ext4_ext_map_blocks`. Identifying the upstream functions will give us crucial context and help formulate more targeted fuzzing strategies.

{
  "Expression": "ext4_ext_map_blocks",
  "PathPrefix": "fs/ext4/"
}

{
  "Output": "fs/ext4/ext4.h=3872=extern int ext4_ext_index_trans_blocks(struct inode *inode, int extents);\nfs/ext4/ext4.h:3873:extern int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,\nfs/ext4/ext4.h-3874-\t\t\t       struct ext4_map_blocks *map, int flags);\n--\nfs/ext4/extents-test.c=524=static const struct kunit_ext_test_param test_split_convert_params[] = {\n--\nfs/ext4/extents-test.c-712-\nfs/ext4/extents-test.c:713:/* Tests to trigger ext4_ext_map_blocks() -\u003e convert_initialized_extent() */\nfs/ext4/extents-test.c-714-static const struct kunit_ext_test_param test_convert_initialized_params[] = {\n--\nfs/ext4/extents-test.c-809-\nfs/ext4/extents-test.c:810:/* Tests to trigger ext4_ext_map_blocks() -\u003e ext4_ext_handle_unwritten_exntents() */\nfs/ext4/extents-test.c-811-static const struct kunit_ext_test_param test_handle_unwritten_params[] = {\n--\nfs/ext4/extents.c=3409=static struct ext4_ext_path *ext4_split_extent(handle_t *handle,\n--\nfs/ext4/extents.c-3536-/*\nfs/ext4/extents.c:3537: * This function is called by ext4_ext_map_blocks() if someone tries to write\nfs/ext4/extents.c-3538- * to an unwritten extent. It may result in splitting the unwritten\n--\nfs/ext4/extents.c=3557=ext4_ext_convert_to_initialized(handle_t *handle, struct inode *inode,\n--\nfs/ext4/extents.c-3790-/*\nfs/ext4/extents.c:3791: * This function is called by ext4_ext_map_blocks() from\nfs/ext4/extents.c-3792- * ext4_get_blocks_dio_write() when DIO to write\n--\nfs/ext4/extents.c=3992=ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,\n--\nfs/ext4/extents.c-4090- *\nfs/ext4/extents.c:4091: * This function is called by ext4_ext_map_blocks() after we failed to\nfs/ext4/extents.c-4092- * find blocks that were already in the inode's extent tree.  Hence,\n--\nfs/ext4/extents.c-4117- * cluster EXT4_B2C(sbi, map-\u003em_lblk).\tWe will then return 1 to\nfs/ext4/extents.c:4118: * signal to ext4_ext_map_blocks() that map-\u003em_pblk should be treated\nfs/ext4/extents.c-4119- * as a new \"allocated\" block region.  Otherwise, we will return 0 and\nfs/ext4/extents.c:4120: * ext4_ext_map_blocks() will then allocate one or more new clusters\nfs/ext4/extents.c-4121- * by calling ext4_mb_new_blocks().\n--\nfs/ext4/extents.c=4191=static ext4_lblk_t ext4_ext_determine_insert_hole(struct inode *inode,\n--\nfs/ext4/extents.c-4269- */\nfs/ext4/extents.c:4270:int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,\nfs/ext4/extents.c-4271-\t\t\tstruct ext4_map_blocks *map, int flags)\n--\nfs/ext4/extents.c-4283-\text_debug(inode, \"blocks %u/%u requested\\n\", map-\u003em_lblk, map-\u003em_len);\nfs/ext4/extents.c:4284:\ttrace_ext4_ext_map_blocks_enter(inode, map-\u003em_lblk, map-\u003em_len, flags);\nfs/ext4/extents.c-4285-\n--\nfs/ext4/extents.c-4546-\nfs/ext4/extents.c:4547:\ttrace_ext4_ext_map_blocks_exit(inode, flags, map,\nfs/ext4/extents.c-4548-\t\t\t\t       err ? err : allocated);\n--\nfs/ext4/extents.c=4583=static int ext4_alloc_file_blocks(struct file *file, loff_t offset, loff_t len,\n--\nfs/ext4/extents.c-4651-\t\t\text4_debug(\"inode #%llu: block %u: len %u: \"\nfs/ext4/extents.c:4652:\t\t\t\t   \"ext4_ext_map_blocks returned %d\",\nfs/ext4/extents.c-4653-\t\t\t\t   inode-\u003ei_ino, map.m_lblk,\n--\nfs/ext4/extents.c=5042=int ext4_convert_unwritten_extents(handle_t *handle, struct inode *inode,\n--\nfs/ext4/extents.c-5081-\t\t\t\t     \"inode #%llu: block %u: len %u: \"\nfs/ext4/extents.c:5082:\t\t\t\t     \"ext4_ext_map_blocks returned %d\",\nfs/ext4/extents.c-5083-\t\t\t\t     inode-\u003ei_ino, map.m_lblk,\n--\nfs/ext4/extents.c=5772=ext4_swap_extents(handle_t *handle, struct inode *inode1,\n--\nfs/ext4/extents.c-5954- * returns 0.  Can also return negative error codes.  Derived from\nfs/ext4/extents.c:5955: * ext4_ext_map_blocks().\nfs/ext4/extents.c-5956- */\n--\nfs/ext4/inode.c=462=static void ext4_map_blocks_es_recheck(handle_t *handle,\n--\nfs/ext4/inode.c-479-\tif (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {\nfs/ext4/inode.c:480:\t\tretval = ext4_ext_map_blocks(handle, inode, map, 0);\nfs/ext4/inode.c-481-\t} else {\n--\nfs/ext4/inode.c=504=static int ext4_map_query_blocks_next_in_leaf(handle_t *handle,\n--\nfs/ext4/inode.c-521-\tmap2.m_flags = 0;\nfs/ext4/inode.c:522:\tretval = ext4_ext_map_blocks(handle, inode, \u0026map2, 0);\nfs/ext4/inode.c-523-\n--\nfs/ext4/inode.c=559=int ext4_map_query_blocks(handle_t *handle, struct inode *inode,\n--\nfs/ext4/inode.c-565-\t/*\nfs/ext4/inode.c:566:\t * ext4_ext_map_blocks() may have already cached the full extent, so\nfs/ext4/inode.c-567-\t * search first to avoid taking i_es_lock for writing. The indirect\n--\nfs/ext4/inode.c-574-\tif (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))\nfs/ext4/inode.c:575:\t\tretval = ext4_ext_map_blocks(handle, inode, map, flags);\nfs/ext4/inode.c-576-\telse\n--\nfs/ext4/inode.c=613=int ext4_map_create_blocks(handle_t *handle, struct inode *inode,\n--\nfs/ext4/inode.c-637-\tif (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {\nfs/ext4/inode.c:638:\t\tretval = ext4_ext_map_blocks(handle, inode, map, flags);\nfs/ext4/inode.c-639-\t} else {\n--\nfs/ext4/inode.c-692- *\nfs/ext4/inode.c:693: * If file type is extents based, it will call ext4_ext_map_blocks(),\nfs/ext4/inode.c-694- * Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping\n--\nfs/ext4/inode.c=708=int ext4_map_blocks(handle_t *handle, struct inode *inode,\n--\nfs/ext4/inode.c-810-\t * Note that if blocks have been preallocated\nfs/ext4/inode.c:811:\t * ext4_ext_map_blocks() returns with buffer head unmapped\nfs/ext4/inode.c-812-\t */\n--\nfs/ext4/inode.c-816-\t\t * we continue and do the actual work in\nfs/ext4/inode.c:817:\t\t * ext4_ext_map_blocks()\nfs/ext4/inode.c-818-\t\t */\n"
}

gemini-3.1-pro-preview

null

null

							input: 8628
							output: 33
							thoughts: 169
						

**Analyzing ext4 Block Mapping**

Okay, so I'm digging into the ext4 filesystem code again, specifically the block mapping. It looks like `ext4_ext_map_blocks` is a real workhorse. It's called by a whole bunch of crucial functions: `ext4_map_blocks`, `ext4_map_create_blocks`, `ext4_map_query_blocks`, even things like `ext4_map_blocks_es_recheck`, `ext4_alloc_file_blocks`, and `ext4_convert_unwritten_extents`. That screams *core* extents API function to me, no doubt about it. It's definitely an API entrypoint for ext4 extents.

And then we have `ext4_es_cache_extent`, which seems to be tightly coupled with extent caching. This is interesting. Looks like an important function as well. I'm going to want to understand that better.

I already know `ext4_map_query_blocks` is also an API entrypoint, but I want to dive a little deeper into that, but first, let's see who is calling `ext4_es_cache_extent`.

{
  "Expression": "ext4_es_cache_extent",
  "PathPrefix": "fs/ext4/"
}

{
  "Output": "fs/ext4/extents.c=524=static void ext4_cache_extents(struct inode *inode,\n--\nfs/ext4/extents.c-538-\t\tif (prev \u0026\u0026 (prev != lblk))\nfs/ext4/extents.c:539:\t\t\text4_es_cache_extent(inode, prev, lblk - prev, ~0,\nfs/ext4/extents.c-540-\t\t\t\t\t     EXTENT_STATUS_HOLE, false);\n--\nfs/ext4/extents.c-543-\t\t\tstatus = EXTENT_STATUS_UNWRITTEN;\nfs/ext4/extents.c:544:\t\text4_es_cache_extent(inode, lblk, len,\nfs/ext4/extents.c-545-\t\t\t\t     ext4_ext_pblock(ex), status, false);\n--\nfs/ext4/extents.c=4191=static ext4_lblk_t ext4_ext_determine_insert_hole(struct inode *inode,\n--\nfs/ext4/extents.c-4241-\text_debug(inode, \" -\u003e %u:%u\\n\", hole_start, len);\nfs/ext4/extents.c:4242:\text4_es_cache_extent(inode, hole_start, len, ~0, EXTENT_STATUS_HOLE,\nfs/ext4/extents.c-4243-\t\t\t     false);\n--\nfs/ext4/extents.c=4270=int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,\n--\nfs/ext4/extents.c-4335-\t\t\t\t       EXT4_EX_NOCACHE)))\nfs/ext4/extents.c:4336:\t\t\t\text4_es_cache_extent(inode, ee_block, ee_len,\nfs/ext4/extents.c-4337-\t\t\t\t\t\t     ee_start, status,\n--\nfs/ext4/extents_status.c=842=static int __es_insert_extent(struct inode *inode, struct extent_status *newes,\n--\nfs/ext4/extents_status.c-902- * status tree. This interface is used for modifying extents. To cache\nfs/ext4/extents_status.c:903: * on-disk extents, use ext4_es_cache_extent() instead.\nfs/ext4/extents_status.c-904- */\nfs/ext4/extents_status.c=905=void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,\n--\nfs/ext4/extents_status.c-1014-/*\nfs/ext4/extents_status.c:1015: * ext4_es_cache_extent() inserts information into the extent status tree\nfs/ext4/extents_status.c-1016- * only if there is no existing information about the specified range or\n--\nfs/ext4/extents_status.c-1023- */\nfs/ext4/extents_status.c:1024:void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,\nfs/ext4/extents_status.c-1025-\t\t\t  ext4_lblk_t len, ext4_fsblk_t pblk,\n--\nfs/ext4/extents_status.c-1079-\t__es_insert_extent(inode, \u0026newes, NULL);\nfs/ext4/extents_status.c:1080:\ttrace_ext4_es_cache_extent(inode, \u0026newes);\nfs/ext4/extents_status.c-1081-\text4_es_print_tree(inode);\n--\nfs/ext4/extents_status.h=136=extern void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,\n--\nfs/ext4/extents_status.h-139-\t\t\t\t  bool delalloc_reserve_used);\nfs/ext4/extents_status.h:140:extern void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,\nfs/ext4/extents_status.h-141-\t\t\t\t ext4_lblk_t len, ext4_fsblk_t pblk,\n--\nfs/ext4/inode.c=504=static int ext4_map_query_blocks_next_in_leaf(handle_t *handle,\n--\nfs/ext4/inode.c-524-\tif (retval \u003c= 0) {\nfs/ext4/inode.c:525:\t\text4_es_cache_extent(inode, map-\u003em_lblk, map-\u003em_len,\nfs/ext4/inode.c-526-\t\t\t\t     map-\u003em_pblk, status, true);\n--\nfs/ext4/inode.c-546-\t\t\tstatus == status2) {\nfs/ext4/inode.c:547:\t\text4_es_cache_extent(inode, map-\u003em_lblk,\nfs/ext4/inode.c-548-\t\t\t\t     map-\u003em_len + map2.m_len, map-\u003em_pblk,\n--\nfs/ext4/inode.c-551-\t} else {\nfs/ext4/inode.c:552:\t\text4_es_cache_extent(inode, map-\u003em_lblk, map-\u003em_len,\nfs/ext4/inode.c-553-\t\t\t\t     map-\u003em_pblk, status, true);\n--\nfs/ext4/inode.c=559=int ext4_map_query_blocks(handle_t *handle, struct inode *inode,\n--\nfs/ext4/inode.c-601-\t\t\t\tEXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;\nfs/ext4/inode.c:602:\t\text4_es_cache_extent(inode, map-\u003em_lblk, map-\u003em_len,\nfs/ext4/inode.c-603-\t\t\t\t     map-\u003em_pblk, status, pre_search);\n"
}

gemini-3.1-pro-preview

null

null

							input: 10657
							output: 39
							thoughts: 180
						

**Analyzing the Ext4 Extent Cache Modification**

Okay, so this patch introduces a `pre_search` boolean to `ext4_es_cache_extent`. The critical point is that when this flag is set to true, it performs a read lock and a search *before* doing anything else. That's a definite functional change – a potential point for unexpected behavior and edge cases. Given that, I'm thinking this is a prime candidate for fuzzing. I'll need to focus my attention on these symbols: `ext4_ext_map_blocks`, `ext4_es_cache_extent`, and `ext4_map_query_blocks`.

Now, let me quickly confirm the build configuration dependencies. I want to be sure I understand the necessary setup. It looks like `EXT4_FS` is the main thing I need. Alright, that's what I expected. No special extent-specific configurations are required. Extents are enabled by default within Ext4, so that simplifies things.

Just to be absolutely certain, I'll quickly double-check that `ext4_es_cache_extent` function in `fs/ext4/extents_status.c` to be sure. It's always good to be thorough.

{
  "Expression": "ext4_es_cache_extent",
  "PathPrefix": "fs/ext4/extents_status.c"
}

{
  "Output": "fs/ext4/extents_status.c=842=static int __es_insert_extent(struct inode *inode, struct extent_status *newes,\n--\nfs/ext4/extents_status.c-902- * status tree. This interface is used for modifying extents. To cache\nfs/ext4/extents_status.c:903: * on-disk extents, use ext4_es_cache_extent() instead.\nfs/ext4/extents_status.c-904- */\nfs/ext4/extents_status.c=905=void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,\n--\nfs/ext4/extents_status.c-1014-/*\nfs/ext4/extents_status.c:1015: * ext4_es_cache_extent() inserts information into the extent status tree\nfs/ext4/extents_status.c-1016- * only if there is no existing information about the specified range or\n--\nfs/ext4/extents_status.c-1023- */\nfs/ext4/extents_status.c:1024:void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,\nfs/ext4/extents_status.c-1025-\t\t\t  ext4_lblk_t len, ext4_fsblk_t pblk,\n--\nfs/ext4/extents_status.c-1079-\t__es_insert_extent(inode, \u0026newes, NULL);\nfs/ext4/extents_status.c:1080:\ttrace_ext4_es_cache_extent(inode, \u0026newes);\nfs/ext4/extents_status.c-1081-\text4_es_print_tree(inode);\n"
}

gemini-3.1-pro-preview

null

null

							input: 11615
							output: 33
							thoughts: 151
						

**My Analysis of the Ext4 Extent Cache Optimization**

Okay, so this patch introduces a `pre_search` parameter to `ext4_es_cache_extent`. The goal is clear: optimize the extent cache. It's about avoiding the write lock (`i_es_lock`) on the extent cache if the extent is *already* cached. Smart move. This is a functional change, meaning any ext4 file operation that deals with block mapping or queries is potentially affected. Therefore, it's definitely something we need to fuzz thoroughly.

Let me zero in on the key functions here: `ext4_ext_map_blocks`, `ext4_es_cache_extent` (of course), and `ext4_map_query_blocks`. I need to understand how this `pre_search` parameter interacts with these and what it changes in terms of locking and performance. Since we're dealing with EXT4, `EXT4_FS` is the relevant config.

First, I think I'll quickly check `ext4_map_query_blocks` to see the context of this function. That will set the stage for a more comprehensive review of the changes.

{
  "Expression": "ext4_map_query_blocks",
  "PathPrefix": "fs/ext4/"
}

{
  "Output": "fs/ext4/ext4.h=210=struct ext4_allocation_request {\n--\nfs/ext4/ext4.h-243-/*\nfs/ext4/ext4.h:244: * This is for use in ext4_map_query_blocks() for a special case where we can\nfs/ext4/ext4.h-245- * have a physically and logically contiguous blocks split across two leaf\n--\nfs/ext4/ext4.h-247- * to know whether the returned extent is last in leaf. If yes, then lookup for\nfs/ext4/ext4.h:248: * next in leaf block in ext4_map_query_blocks_next_in_leaf().\nfs/ext4/ext4.h-249- * - This is never going to be added to any buffer head state.\n--\nfs/ext4/ext4.h=684=enum {\n--\nfs/ext4/ext4.h-752-/*\nfs/ext4/ext4.h:753: * ext4_map_query_blocks() uses this filter mask to filter the flags needed to\nfs/ext4/ext4.h-754- * pass while lookup/querying of on disk extent tree.\n--\nfs/ext4/ext4.h=3888=extern int ext4_map_blocks(handle_t *handle, struct inode *inode,\nfs/ext4/ext4.h-3889-\t\t\t   struct ext4_map_blocks *map, int flags);\nfs/ext4/ext4.h:3890:extern int ext4_map_query_blocks(handle_t *handle, struct inode *inode,\nfs/ext4/ext4.h-3891-\t\t\t\t  struct ext4_map_blocks *map, int flags);\n--\nfs/ext4/extents-test.c=358=static int check_buffer(char *buf, int c, int size)\n--\nfs/ext4/extents-test.c-372-/*\nfs/ext4/extents-test.c:373: * Simulate a map block call by first calling ext4_map_query_blocks() to\nfs/ext4/extents-test.c-374- * correctly populate map flags and pblk and then call the\n--\nfs/ext4/extents-test.c=379=static void ext4_map_create_blocks_helper(struct kunit *test,\n--\nfs/ext4/extents-test.c-385-\nfs/ext4/extents-test.c:386:\tretval = ext4_map_query_blocks(NULL, inode, map, flags);\nfs/ext4/extents-test.c-387-\tif (retval \u003c 0) {\nfs/ext4/extents-test.c-388-\t\tKUNIT_FAIL(test,\nfs/ext4/extents-test.c:389:\t\t\t   \"ext4_map_query_blocks() failed. Cannot proceed\\n\");\nfs/ext4/extents-test.c-390-\t\treturn;\n--\nfs/ext4/extents.c=6315=EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_issue_zeroout);\nfs/ext4/extents.c:6316:EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_map_query_blocks);\nfs/ext4/extents.c-6317-#endif\n--\nfs/ext4/inode.c=462=static void ext4_map_blocks_es_recheck(handle_t *handle,\n--\nfs/ext4/inode.c-503-\nfs/ext4/inode.c:504:static int ext4_map_query_blocks_next_in_leaf(handle_t *handle,\nfs/ext4/inode.c-505-\t\t\tstruct inode *inode, struct ext4_map_blocks *map,\n--\nfs/ext4/inode.c-558-\nfs/ext4/inode.c:559:int ext4_map_query_blocks(handle_t *handle, struct inode *inode,\nfs/ext4/inode.c-560-\t\t\t  struct ext4_map_blocks *map, int flags)\n--\nfs/ext4/inode.c-604-\t} else {\nfs/ext4/inode.c:605:\t\tretval = ext4_map_query_blocks_next_in_leaf(handle, inode, map,\nfs/ext4/inode.c-606-\t\t\t\t\t\t\t    orig_mlen);\n--\nfs/ext4/inode.c=708=int ext4_map_blocks(handle_t *handle, struct inode *inode,\n--\nfs/ext4/inode.c-792-\tdown_read(\u0026EXT4_I(inode)-\u003ei_data_sem);\nfs/ext4/inode.c:793:\tretval = ext4_map_query_blocks(handle, inode, map, flags);\nfs/ext4/inode.c-794-\tup_read((\u0026EXT4_I(inode)-\u003ei_data_sem));\n--\nfs/ext4/inode.c=1923=static int ext4_da_map_blocks(struct inode *inode, struct ext4_map_blocks *map)\n--\nfs/ext4/inode.c-1978-\telse\nfs/ext4/inode.c:1979:\t\tretval = ext4_map_query_blocks(NULL, inode, map, 0);\nfs/ext4/inode.c-1980-\tup_read(\u0026EXT4_I(inode)-\u003ei_data_sem);\n--\nfs/ext4/inode.c-2001-\t} else if (!ext4_has_inline_data(inode)) {\nfs/ext4/inode.c:2002:\t\tretval = ext4_map_query_blocks(NULL, inode, map, 0);\nfs/ext4/inode.c-2003-\t\tif (retval) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 13551
							output: 139
							thoughts: 86
						

Okay, here's my take on those code paths.

**Focus Areas in the ext4 Block Mapping Landscape**

Right, so I'm thinking about performance bottlenecks in the ext4 filesystem, and where I should be concentrating my efforts. The `ext4_map_query_blocks` function is definitely a key spot. It's essentially the workhorse, being called by both `ext4_map_blocks` and `ext4_da_map_blocks`. That immediately flags it as a *very* common and potentially critical path for optimization. The implications of this are that any inefficiencies here are amplified across the board.

Since `ext4_map_query_blocks` is so central, I should also look closely at its callers. So, `ext4_ext_map_blocks` and `ext4_es_cache_extent` also seem like excellent candidates for in-depth analysis. They directly feed into the core block mapping process. I'll need to understand what's happening in those functions and how they influence `ext4_map_query_blocks`.

Alright, I'll set the results.

{
  "EnableConfigs": [
    "EXT4_FS"
  ],
  "FocusSymbols": [
    "ext4_ext_map_blocks",
    "ext4_es_cache_extent",
    "ext4_map_query_blocks"
  ],
  "Reasoning": "The patch modifies the ext4 extent status caching logic by introducing a `pre_search` parameter to `ext4_es_cache_extent`. This allows avoiding a write lock if the extent is already cached, optimizing block mapping and querying operations. This is a functional change in the core ext4 filesystem logic and is reachable via standard file operations.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "EXT4_FS"
  ],
  "FocusSymbols": [
    "ext4_ext_map_blocks",
    "ext4_es_cache_extent",
    "ext4_map_query_blocks"
  ],
  "Reasoning": "The patch modifies the ext4 extent status caching logic by introducing a `pre_search` parameter to `ext4_es_cache_extent`. This allows avoiding a write lock if the extent is already cached, optimizing block mapping and querying operations. This is a functional change in the core ext4 filesystem logic and is reachable via standard file operations.",
  "WorthFuzzing": true
}