AI Trajectory

null

{
  "EnableConfigs": [
    "EXT4_FS",
    "FS_DAX"
  ],
  "FocusSymbols": [
    "ext4_dio_needs_zeroing",
    "ext4_buffered_write_iter",
    "ext4_dio_write_checks",
    "ext4_dax_write_iter",
    "ext4_iomap_alloc"
  ],
  "Reasoning": "The patch modifies ext4 direct I/O and buffered I/O logic, specifically handling unaligned DIO writes and partial block zeroing, as well as adding NOWAIT support in DAX and iomap allocation. These are reachable core filesystem logic changes that should be fuzzed.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 051a7afe10013671b75b6c4c07898788a67f662e\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Jun 29 12:05:51 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/fs/ext4/file.c b/fs/ext4/file.c\nindex eb1a323962b101..9a16071b719d78 100644\n--- a/fs/ext4/file.c\n+++ b/fs/ext4/file.c\n@@ -213,31 +213,60 @@ ext4_extending_io(struct inode *inode, loff_t offset, size_t len)\n \treturn false;\n }\n \n-/* Is IO overwriting allocated or initialized blocks? */\n-static bool ext4_overwrite_io(struct inode *inode,\n-\t\t\t      loff_t pos, loff_t len, bool *unwritten)\n+/*\n+ * Does an unaligned DIO write require partial block zeroing?\n+ *\n+ * Partial block zeroing is performed only for the head and tail blocks\n+ * when they are partially covered by the write and the underlying extent\n+ * is a hole or unwritten. Middle blocks (fully covered by the write)\n+ * are written as whole blocks without zeroing.\n+ *\n+ * When zeroing is required, two concurrent unaligned DIO writes to the\n+ * same partial block can race and corrupt each other's data, so the\n+ * caller must take the exclusive i_rwsem and drain in-flight DIO. When\n+ * zeroing is not required, shared lock is safe -- block allocation and\n+ * unwritten conversion for middle blocks are protected by i_data_sem\n+ * and inode_dio_begin().\n+ */\n+static bool ext4_dio_needs_zeroing(struct inode *inode, loff_t pos, loff_t len)\n {\n \tstruct ext4_map_blocks map;\n \tunsigned int blkbits = inode-\u003ei_blkbits;\n-\tint err, blklen;\n+\tunsigned long blockmask = inode-\u003ei_sb-\u003es_blocksize - 1;\n+\tbool head_partial, tail_partial;\n+\text4_lblk_t head_lblk, tail_lblk;\n+\tint err;\n \n \tif (pos + len \u003e i_size_read(inode))\n-\t\treturn false;\n+\t\treturn true;\n \n-\tmap.m_lblk = pos \u003e\u003e blkbits;\n-\tmap.m_len = EXT4_MAX_BLOCKS(len, pos, blkbits);\n-\tblklen = map.m_len;\n+\thead_partial = (pos \u0026 blockmask) != 0;\n+\ttail_partial = ((pos + len) \u0026 blockmask) != 0;\n+\thead_lblk = pos \u003e\u003e blkbits;\n+\ttail_lblk = (pos + len - 1) \u003e\u003e blkbits;\n+\n+\t/* Check the head partial block. */\n+\tif (head_partial) {\n+\t\tmap.m_lblk = head_lblk;\n+\t\tmap.m_len = tail_lblk - head_lblk + 1;\n+\t\terr = ext4_map_blocks(NULL, inode, \u0026map, 0);\n+\t\tif (err \u003c= 0 || !(map.m_flags \u0026 EXT4_MAP_MAPPED))\n+\t\t\treturn true;\n+\t\t/* If this mapping already covers the tail block, we're done. */\n+\t\tif (!tail_partial || map.m_lblk + err \u003e tail_lblk)\n+\t\t\treturn false;\n+\t}\n \n-\terr = ext4_map_blocks(NULL, inode, \u0026map, 0);\n-\tif (err != blklen)\n-\t\treturn false;\n-\t/*\n-\t * 'err==len' means that all of the blocks have been preallocated,\n-\t * regardless of whether they have been initialized or not. We need to\n-\t * check m_flags to distinguish the unwritten extents.\n-\t */\n-\t*unwritten = !(map.m_flags \u0026 EXT4_MAP_MAPPED);\n-\treturn true;\n+\t/* Check the tail partial block. */\n+\tif (tail_partial) {\n+\t\tmap.m_lblk = tail_lblk;\n+\t\tmap.m_len = 1;\n+\t\terr = ext4_map_blocks(NULL, inode, \u0026map, 0);\n+\t\tif (err \u003c= 0 || !(map.m_flags \u0026 EXT4_MAP_MAPPED))\n+\t\t\treturn true;\n+\t}\n+\n+\treturn false;\n }\n \n static ssize_t ext4_generic_write_checks(struct kiocb *iocb,\n@@ -278,7 +307,7 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)\n \tif (count \u003c= 0)\n \t\treturn count;\n \n-\tret = file_modified(iocb-\u003eki_filp);\n+\tret = kiocb_modified(iocb);\n \tif (ret)\n \t\treturn ret;\n \n@@ -309,6 +338,13 @@ static ssize_t ext4_buffered_write_iter(struct kiocb *iocb,\n \t\treturn -EOPNOTSUPP;\n \n \tinode_lock(inode);\n+\n+\t/*\n+\t * Prevent concurrent direct I/O and buffered I/O to the same file\n+\t * range. Wait for in-flight DIO to finish before dirtying pages.\n+\t */\n+\tinode_dio_wait(inode);\n+\n \tret = ext4_write_checks(iocb, from);\n \tif (ret \u003c= 0)\n \t\tgoto out;\n@@ -428,16 +464,28 @@ static const struct iomap_dio_ops ext4_dio_write_ops = {\n  * condition requires an exclusive inode lock. If yes, then we restart the\n  * whole operation by releasing the shared lock and acquiring exclusive lock.\n  *\n- * - For unaligned_io we never take shared lock as it may cause data corruption\n- *   when two unaligned IO tries to modify the same block e.g. while zeroing.\n+ * The decision is layered, evaluated in this order:\n  *\n- * - For extending writes case we don't take the shared lock, since it requires\n- *   updating inode i_disksize and/or orphan handling with exclusive lock.\n+ * 1. If kiocb_modified() needs to update security info (!IS_NOSEC), upgrade\n+ *    to the exclusive lock -- the security update itself requires it,\n+ *    regardless of whether the write extends the file or is aligned.\n  *\n- * - shared locking will only be true mostly with overwrites, including\n- *   initialized blocks and unwritten blocks.\n+ * 2. If the write extends i_size or i_disksize, upgrade to the exclusive\n+ *    lock to safely update i_disksize and the orphan list, regardless of\n+ *    alignment.\n  *\n- * - Otherwise we will switch to exclusive i_rwsem lock.\n+ * 3. Otherwise, for aligned non-extending writes, shared lock is always\n+ *    sufficient regardless of extent state (written, unwritten, or hole).\n+ *    truncate/punch_hole cannot run while we hold the shared i_rwsem\n+ *    (they need it exclusively); after we release it, inode_dio_begin()\n+ *    keeps their inode_dio_wait() blocked until in-flight bios complete.\n+ *    i_data_sem serializes concurrent extent tree modifications.\n+ *\n+ * 4. Otherwise, the write is unaligned and non-extending. Shared lock is\n+ *    safe unless the DIO layer needs to perform partial block zeroing --\n+ *    i.e. the head or tail partial block sits on a hole or unwritten\n+ *    extent. In that case upgrade to the exclusive lock and drain\n+ *    in-flight DIO to avoid races with concurrent partial block zeroing.\n  */\n static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,\n \t\t\t\t     bool *ilock_shared, bool *extend,\n@@ -448,7 +496,7 @@ static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,\n \tloff_t offset;\n \tsize_t count;\n \tssize_t ret;\n-\tbool overwrite, unaligned_io, unwritten;\n+\tbool needs_zeroing = false;\n \n restart:\n \tret = ext4_generic_write_checks(iocb, from);\n@@ -458,24 +506,22 @@ static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,\n \toffset = iocb-\u003eki_pos;\n \tcount = ret;\n \n-\tunaligned_io = ext4_unaligned_io(inode, from, offset);\n \t*extend = ext4_extending_io(inode, offset, count);\n-\toverwrite = ext4_overwrite_io(inode, offset, count, \u0026unwritten);\n \n \t/*\n-\t * Determine whether we need to upgrade to an exclusive lock. This is\n-\t * required to change security info in file_modified(), for extending\n-\t * I/O, any form of non-overwrite I/O, and unaligned I/O to unwritten\n-\t * extents (as partial block zeroing may be required).\n+\t * For unaligned writes, check whether partial block zeroing will be\n+\t * needed. If so, exclusive lock is required to serialize against\n+\t * concurrent DIO that could race with the zeroing.\n \t *\n-\t * Note that unaligned writes are allowed under shared lock so long as\n-\t * they are pure overwrites. Otherwise, concurrent unaligned writes risk\n-\t * data corruption due to partial block zeroing in the dio layer, and so\n-\t * the I/O must occur exclusively.\n+\t * For aligned writes we skip this check entirely since allocation\n+\t * under shared lock is safe.\n \t */\n+\tif (ext4_unaligned_io(inode, from, offset))\n+\t\tneeds_zeroing = ext4_dio_needs_zeroing(inode, offset, count);\n+\n+\t/* Determine whether we need to upgrade to an exclusive lock. */\n \tif (*ilock_shared \u0026\u0026\n-\t    ((!IS_NOSEC(inode) || *extend || !overwrite ||\n-\t     (unaligned_io \u0026\u0026 unwritten)))) {\n+\t    (!IS_NOSEC(inode) || *extend || needs_zeroing)) {\n \t\tif (iocb-\u003eki_flags \u0026 IOCB_NOWAIT) {\n \t\t\tret = -EAGAIN;\n \t\t\tgoto out;\n@@ -489,21 +535,28 @@ static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,\n \t/*\n \t * Now that locking is settled, determine dio flags and exclusivity\n \t * requirements. We don't use DIO_OVERWRITE_ONLY because we enforce\n-\t * behavior already. The inode lock is already held exclusive if the\n-\t * write is non-overwrite or extending, so drain all outstanding dio and\n-\t * set the force wait dio flag.\n+\t * behavior already. When holding the exclusive lock for a write that\n+\t * needs partial block zeroing or is extending the file, we must wait\n+\t * for the I/O to complete synchronously:\n+\t *\n+\t *  - needs_zeroing: drain in-flight DIO whose end_io could race with\n+\t *    our partial block zeroing, and force synchronous completion so we\n+\t *    don't leave in-flight zeroing bios for the next writer to drain.\n+\t *\n+\t *  - extend: the caller must update i_disksize after I/O completion,\n+\t *    which requires the data to be on disk first.\n \t */\n-\tif (!*ilock_shared \u0026\u0026 (unaligned_io || *extend)) {\n+\tif (!*ilock_shared \u0026\u0026 (needs_zeroing || *extend)) {\n \t\tif (iocb-\u003eki_flags \u0026 IOCB_NOWAIT) {\n \t\t\tret = -EAGAIN;\n \t\t\tgoto out;\n \t\t}\n-\t\tif (unaligned_io \u0026\u0026 (!overwrite || unwritten))\n+\t\tif (needs_zeroing)\n \t\t\tinode_dio_wait(inode);\n \t\t*dio_flags = IOMAP_DIO_FORCE_WAIT;\n \t}\n \n-\tret = file_modified(file);\n+\tret = kiocb_modified(iocb);\n \tif (ret \u003c 0)\n \t\tgoto out;\n \n@@ -672,6 +725,11 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)\n \tcount = iov_iter_count(from);\n \n \tif (offset + count \u003e EXT4_I(inode)-\u003ei_disksize) {\n+\t\tif (iocb-\u003eki_flags \u0026 IOCB_NOWAIT) {\n+\t\t\tret = -EAGAIN;\n+\t\t\tgoto out;\n+\t\t}\n+\n \t\thandle = ext4_journal_start(inode, EXT4_HT_INODE, 2);\n \t\tif (IS_ERR(handle)) {\n \t\t\tret = PTR_ERR(handle);\ndiff --git a/fs/ext4/inode.c b/fs/ext4/inode.c\nindex c2c2d6ac7f3d13..832794294ccffe 100644\n--- a/fs/ext4/inode.c\n+++ b/fs/ext4/inode.c\n@@ -3672,6 +3672,9 @@ static int ext4_iomap_alloc(struct inode *inode, struct ext4_map_blocks *map,\n \tint ret, dio_credits, m_flags = 0, retries = 0;\n \tbool force_commit = false;\n \n+\tif (flags \u0026 IOMAP_NOWAIT)\n+\t\treturn -EAGAIN;\n+\n \t/*\n \t * Trim the mapping request to the maximum value that we can map at\n \t * once for direct I/O.\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "EXT4_FS",
    "FS_DAX"
  ],
  "FocusSymbols": [
    "ext4_dio_needs_zeroing",
    "ext4_buffered_write_iter",
    "ext4_dio_write_checks",
    "ext4_dax_write_iter",
    "ext4_iomap_alloc"
  ],
  "Reasoning": "The patch modifies ext4 direct I/O and buffered I/O logic, specifically handling unaligned DIO writes and partial block zeroing, as well as adding NOWAIT support in DAX and iomap allocation. These are reachable core filesystem logic changes that 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).

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 051a7afe10013671b75b6c4c07898788a67f662e
Author: syz-cluster <triage@syzkaller.com>
Date:   Mon Jun 29 12:05:51 2026 +0000

    syz-cluster: applied patch under review

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index eb1a323962b101..9a16071b719d78 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -213,31 +213,60 @@ ext4_extending_io(struct inode *inode, loff_t offset, size_t len)
 	return false;
 }
 
-/* Is IO overwriting allocated or initialized blocks? */
-static bool ext4_overwrite_io(struct inode *inode,
-			      loff_t pos, loff_t len, bool *unwritten)
+/*
+ * Does an unaligned DIO write require partial block zeroing?
+ *
+ * Partial block zeroing is performed only for the head and tail blocks
+ * when they are partially covered by the write and the underlying extent
+ * is a hole or unwritten. Middle blocks (fully covered by the write)
+ * are written as whole blocks without zeroing.
+ *
+ * When zeroing is required, two concurrent unaligned DIO writes to the
+ * same partial block can race and corrupt each other's data, so the
+ * caller must take the exclusive i_rwsem and drain in-flight DIO. When
+ * zeroing is not required, shared lock is safe -- block allocation and
+ * unwritten conversion for middle blocks are protected by i_data_sem
+ * and inode_dio_begin().
+ */
+static bool ext4_dio_needs_zeroing(struct inode *inode, loff_t pos, loff_t len)
 {
 	struct ext4_map_blocks map;
 	unsigned int blkbits = inode->i_blkbits;
-	int err, blklen;
+	unsigned long blockmask = inode->i_sb->s_blocksize - 1;
+	bool head_partial, tail_partial;
+	ext4_lblk_t head_lblk, tail_lblk;
+	int err;
 
 	if (pos + len > i_size_read(inode))
-		return false;
+		return true;
 
-	map.m_lblk = pos >> blkbits;
-	map.m_len = EXT4_MAX_BLOCKS(len, pos, blkbits);
-	blklen = map.m_len;
+	head_partial = (pos & blockmask) != 0;
+	tail_partial = ((pos + len) & blockmask) != 0;
+	head_lblk = pos >> blkbits;
+	tail_lblk = (pos + len - 1) >> blkbits;
+
+	/* Check the head partial block. */
+	if (head_partial) {
+		map.m_lblk = head_lblk;
+		map.m_len = tail_lblk - head_lblk + 1;
+		err = ext4_map_blocks(NULL, inode, &map, 0);
+		if (err <= 0 || !(map.m_flags & EXT4_MAP_MAPPED))
+			return true;
+		/* If this mapping already covers the tail block, we're done. */
+		if (!tail_partial || map.m_lblk + err > tail_lblk)
+			return false;
+	}
 
-	err = ext4_map_blocks(NULL, inode, &map, 0);
-	if (err != blklen)
-		return false;
-	/*
-	 * 'err==len' means that all of the blocks have been preallocated,
-	 * regardless of whether they have been initialized or not. We need to
-	 * check m_flags to distinguish the unwritten extents.
-	 */
-	*unwritten = !(map.m_flags & EXT4_MAP_MAPPED);
-	return true;
+	/* Check the tail partial block. */
+	if (tail_partial) {
+		map.m_lblk = tail_lblk;
+		map.m_len = 1;
+		err = ext4_map_blocks(NULL, inode, &map, 0);
+		if (err <= 0 || !(map.m_flags & EXT4_MAP_MAPPED))
+			return true;
+	}
+
+	return false;
 }
 
 static ssize_t ext4_generic_write_checks(struct kiocb *iocb,
@@ -278,7 +307,7 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
 	if (count <= 0)
 		return count;
 
-	ret = file_modified(iocb->ki_filp);
+	ret = kiocb_modified(iocb);
 	if (ret)
 		return ret;
 
@@ -309,6 +338,13 @@ static ssize_t ext4_buffered_write_iter(struct kiocb *iocb,
 		return -EOPNOTSUPP;
 
 	inode_lock(inode);
+
+	/*
+	 * Prevent concurrent direct I/O and buffered I/O to the same file
+	 * range. Wait for in-flight DIO to finish before dirtying pages.
+	 */
+	inode_dio_wait(inode);
+
 	ret = ext4_write_checks(iocb, from);
 	if (ret <= 0)
 		goto out;
@@ -428,16 +464,28 @@ static const struct iomap_dio_ops ext4_dio_write_ops = {
  * condition requires an exclusive inode lock. If yes, then we restart the
  * whole operation by releasing the shared lock and acquiring exclusive lock.
  *
- * - For unaligned_io we never take shared lock as it may cause data corruption
- *   when two unaligned IO tries to modify the same block e.g. while zeroing.
+ * The decision is layered, evaluated in this order:
  *
- * - For extending writes case we don't take the shared lock, since it requires
- *   updating inode i_disksize and/or orphan handling with exclusive lock.
+ * 1. If kiocb_modified() needs to update security info (!IS_NOSEC), upgrade
+ *    to the exclusive lock -- the security update itself requires it,
+ *    regardless of whether the write extends the file or is aligned.
  *
- * - shared locking will only be true mostly with overwrites, including
- *   initialized blocks and unwritten blocks.
+ * 2. If the write extends i_size or i_disksize, upgrade to the exclusive
+ *    lock to safely update i_disksize and the orphan list, regardless of
+ *    alignment.
  *
- * - Otherwise we will switch to exclusive i_rwsem lock.
+ * 3. Otherwise, for aligned non-extending writes, shared lock is always
+ *    sufficient regardless of extent state (written, unwritten, or hole).
+ *    truncate/punch_hole cannot run while we hold the shared i_rwsem
+ *    (they need it exclusively); after we release it, inode_dio_begin()
+ *    keeps their inode_dio_wait() blocked until in-flight bios complete.
+ *    i_data_sem serializes concurrent extent tree modifications.
+ *
+ * 4. Otherwise, the write is unaligned and non-extending. Shared lock is
+ *    safe unless the DIO layer needs to perform partial block zeroing --
+ *    i.e. the head or tail partial block sits on a hole or unwritten
+ *    extent. In that case upgrade to the exclusive lock and drain
+ *    in-flight DIO to avoid races with concurrent partial block zeroing.
  */
 static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,
 				     bool *ilock_shared, bool *extend,
@@ -448,7 +496,7 @@ static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,
 	loff_t offset;
 	size_t count;
 	ssize_t ret;
-	bool overwrite, unaligned_io, unwritten;
+	bool needs_zeroing = false;
 
 restart:
 	ret = ext4_generic_write_checks(iocb, from);
@@ -458,24 +506,22 @@ static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,
 	offset = iocb->ki_pos;
 	count = ret;
 
-	unaligned_io = ext4_unaligned_io(inode, from, offset);
 	*extend = ext4_extending_io(inode, offset, count);
-	overwrite = ext4_overwrite_io(inode, offset, count, &unwritten);
 
 	/*
-	 * Determine whether we need to upgrade to an exclusive lock. This is
-	 * required to change security info in file_modified(), for extending
-	 * I/O, any form of non-overwrite I/O, and unaligned I/O to unwritten
-	 * extents (as partial block zeroing may be required).
+	 * For unaligned writes, check whether partial block zeroing will be
+	 * needed. If so, exclusive lock is required to serialize against
+	 * concurrent DIO that could race with the zeroing.
 	 *
-	 * Note that unaligned writes are allowed under shared lock so long as
-	 * they are pure overwrites. Otherwise, concurrent unaligned writes risk
-	 * data corruption due to partial block zeroing in the dio layer, and so
-	 * the I/O must occur exclusively.
+	 * For aligned writes we skip this check entirely since allocation
+	 * under shared lock is safe.
 	 */
+	if (ext4_unaligned_io(inode, from, offset))
+		needs_zeroing = ext4_dio_needs_zeroing(inode, offset, count);
+
+	/* Determine whether we need to upgrade to an exclusive lock. */
 	if (*ilock_shared &&
-	    ((!IS_NOSEC(inode) || *extend || !overwrite ||
-	     (unaligned_io && unwritten)))) {
+	    (!IS_NOSEC(inode) || *extend || needs_zeroing)) {
 		if (iocb->ki_flags & IOCB_NOWAIT) {
 			ret = -EAGAIN;
 			goto out;
@@ -489,21 +535,28 @@ static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,
 	/*
 	 * Now that locking is settled, determine dio flags and exclusivity
 	 * requirements. We don't use DIO_OVERWRITE_ONLY because we enforce
-	 * behavior already. The inode lock is already held exclusive if the
-	 * write is non-overwrite or extending, so drain all outstanding dio and
-	 * set the force wait dio flag.
+	 * behavior already. When holding the exclusive lock for a write that
+	 * needs partial block zeroing or is extending the file, we must wait
+	 * for the I/O to complete synchronously:
+	 *
+	 *  - needs_zeroing: drain in-flight DIO whose end_io could race with
+	 *    our partial block zeroing, and force synchronous completion so we
+	 *    don't leave in-flight zeroing bios for the next writer to drain.
+	 *
+	 *  - extend: the caller must update i_disksize after I/O completion,
+	 *    which requires the data to be on disk first.
 	 */
-	if (!*ilock_shared && (unaligned_io || *extend)) {
+	if (!*ilock_shared && (needs_zeroing || *extend)) {
 		if (iocb->ki_flags & IOCB_NOWAIT) {
 			ret = -EAGAIN;
 			goto out;
 		}
-		if (unaligned_io && (!overwrite || unwritten))
+		if (needs_zeroing)
 			inode_dio_wait(inode);
 		*dio_flags = IOMAP_DIO_FORCE_WAIT;
 	}
 
-	ret = file_modified(file);
+	ret = kiocb_modified(iocb);
 	if (ret < 0)
 		goto out;
 
@@ -672,6 +725,11 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	count = iov_iter_count(from);
 
 	if (offset + count > EXT4_I(inode)->i_disksize) {
+		if (iocb->ki_flags & IOCB_NOWAIT) {
+			ret = -EAGAIN;
+			goto out;
+		}
+
 		handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
 		if (IS_ERR(handle)) {
 			ret = PTR_ERR(handle);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c2c2d6ac7f3d13..832794294ccffe 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3672,6 +3672,9 @@ static int ext4_iomap_alloc(struct inode *inode, struct ext4_map_blocks *map,
 	int ret, dio_credits, m_flags = 0, retries = 0;
 	bool force_commit = false;
 
+	if (flags & IOMAP_NOWAIT)
+		return -EAGAIN;
+
 	/*
 	 * Trim the mapping request to the maximum value that we can map at
 	 * once for direct I/O.

gemini-3.1-pro-preview

null

null

							input: 5066
							output: 30
							thoughts: 337
						

**My Assessment of the ext4 Patch**

Okay, so I've got this patch in front of me, and it's making some pretty fundamental changes deep within the ext4 filesystem. The core of it seems to be in `fs/ext4/file.c` and `fs/ext4/inode.c`, so we're talking about direct I/O and buffered I/O, particularly around how we handle locking and partial block zeroing when doing unaligned direct I/O writes.

My initial thought is that this demands a thorough fuzzing campaign. The patch introduces `ext4_dio_needs_zeroing`, which seems to be a replacement for `ext4_overwrite_io`, and that alone raises a red flag for potential edge cases. We also have `inode_dio_wait(inode)` now being called from `ext4_buffered_write_iter`, which is interesting. Replacing `file_modified` with `kiocb_modified` is another point to investigate. The addition of `IOCB_NOWAIT` checks in `ext4_dax_write_iter` and `IOMAP_NOWAIT` in `ext4_iomap_alloc` also are of particular interest.

To make sure we can efficiently test this, I need to focus on the key functions that have been modified or introduced. From what I can tell, I should prioritize fuzzing:
*   `ext4_dio_needs_zeroing`
*   `ext4_buffered_write_iter`
*   `ext4_dio_write_checks`
*   `ext4_dax_write_iter`
*   `ext4_iomap_alloc`

Now, before I start generating test cases, I need to verify which configurations I need to trigger the changes. I know the code is under `fs/ext4/`, so obviously, `EXT4_FS` is a must. Does this depend on `FS_DAX` or `EXT4_FS_DAX`? I'll need to double-check that to make sure I'm testing the code paths correctly.

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

{
  "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: 6104
							output: 33
							thoughts: 7
						

Okay, let's dive into this. Here's how I'd approach summarizing the "Thoughts" based on the prompt, as an expert in my field:

**Assessing the DAX Landscape**

Alright, the initial prompt is pretty direct: "Let's check DAX." Immediately, my mind jumps to the specifics. What kind of check are we talking about? Is it a general overview of the market index? Perhaps a deep dive into the underlying fundamentals of the companies within the DAX? Or, am I looking at a specific strategy or investment opportunity related to the DAX? I need to clarify the context. The prompt is a launchpad; it demands further probing. My expertise allows me to immediately begin mentally cataloging the potential avenues of exploration. I'm ready to move forward.

no matches

{
  "Expression": "config EXT4_FS_DAX",
  "PathPrefix": "fs/ext4/"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 6325
							output: 29
							thoughts: 37
						

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

**Investigating DAX Configuration Within Ext4**

Right, let's get down to brass tacks. I need to refresh my memory on how DAX is configured within the Ext4 filesystem. My initial thought is to zero in on the relevant config files. The obvious starting points are the `config.*DAX` files. I know they're probably located within the `fs/ext4/` directory, and maybe the core `fs/dax.c` file as well. Alternatively, I know I might find details within the `fs/ext4/Kconfig` file. I'll need to sift through these files to nail down the specific configuration options and their dependencies. This is where the core logic usually sits.

no matches

{
  "Expression": "DAX",
  "PathPrefix": "fs/ext4/Kconfig"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 6579
							output: 37
							thoughts: 26
						

Here's my take on those thoughts, tailored for an expert audience:

**Diving into ext4_dax_write_iter**

Okay, time to get my hands dirty with `ext4_dax_write_iter` in `fs/ext4/file.c`. I need to refresh my understanding of how DAX writes are handled at this level in ext4. I'm particularly interested in how they integrate with the iterators. I'll be looking for nuances around direct I/O, potential optimizations for DAX-aware hardware, and the locking semantics employed during the write process. I'm anticipating some intricate interactions with the block allocation routines and the inode data structures – I hope they're not causing any issues. I'll pay close attention to the error handling paths; DAX introduces some failure possibilities that aren't typical of regular buffered writes, and I want to make sure those are properly covered. Need to track down where the page mapping occurs... right, it is likely involved.

{
  "Expression": "ext4_dax_write_iter",
  "PathPrefix": "fs/ext4/file.c"
}

{
  "Output": "fs/ext4/file.c=703=static ssize_t\nfs/ext4/file.c:704:ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)\nfs/ext4/file.c-705-{\n--\nfs/ext4/file.c=764=ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/ext4/file.c-774-\tif (IS_DAX(inode))\nfs/ext4/file.c:775:\t\treturn ext4_dax_write_iter(iocb, from);\nfs/ext4/file.c-776-#endif\n"
}

gemini-3.1-pro-preview

null

null

							input: 7052
							output: 36
							thoughts: 38
						

Okay, let's see... I'm pretty sure this specific issue with direct access (DAX) file systems is handled under the `#ifdef CONFIG_FS_DAX` preprocessor directive. That's usually where DAX-specific code resides. Right, so where would that manifest in the ext4 code? Hmm, logically, in the file handling area... probably `fs/ext4/file.c` makes the most sense. Now, let's see, the core file operations... that sounds like a good starting point. Line 703 sounds reasonable, it's generally in the vicinity of file I/O operations and might contain logic relating to reading, writing, and handling of direct access. I'll take a look right around there and see what's happening.

{
  "File": "fs/ext4/file.c",
  "FirstLine": 695,
  "LineCount": 20
}

{
  "Contents": " 695:\t\t\t\t\t\t\t offset \u003e\u003e PAGE_SHIFT,\n 696:\t\t\t\t\t\t\t endbyte \u003e\u003e PAGE_SHIFT);\n 697:\t\t}\n 698:\t\n 699:\t\treturn ret;\n 700:\t}\n 701:\t\n 702:\t#ifdef CONFIG_FS_DAX\n 703:\tstatic ssize_t\n 704:\text4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)\n 705:\t{\n 706:\t\tssize_t ret;\n 707:\t\tsize_t count;\n 708:\t\tloff_t offset;\n 709:\t\thandle_t *handle;\n 710:\t\tbool extend = false;\n 711:\t\tstruct inode *inode = file_inode(iocb-\u003eki_filp);\n 712:\t\n 713:\t\tif (iocb-\u003eki_flags \u0026 IOCB_NOWAIT) {\n 714:\t\t\tif (!inode_trylock(inode))\n"
}

gemini-3.1-pro-preview

null

null

							input: 7572
							output: 37
							thoughts: 82
						

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

**Checking DAX and EXT4 Configuration for Optimal Performance**

Alright, let's see, confirmed: `CONFIG_FS_DAX` is what we're targeting. Now, I need to make absolutely sure everything is set up correctly for DAX functionality. I'll make a note that `EXT4_FS` is a critical part of the puzzle along with `FS_DAX`. Even though I know `EXT4_FS` is generally enabled, it's always a good practice to explicitly state its importance in this context for clarity.

My next immediate task is to examine `ext4_dio_needs_zeroing` within `fs/ext4/file.c`. I need to ensure there are no unnecessary zeroing operations happening that might impact the direct access performance of DAX-enabled ext4 filesystems. That's where the real optimization opportunities likely lie. I'll focus on potential overhead when dealing with persistent memory.

{
  "Expression": "ext4_dio_needs_zeroing",
  "PathPrefix": "fs/ext4/file.c"
}

{
  "Output": "fs/ext4/file.c=208=ext4_extending_io(struct inode *inode, loff_t offset, size_t len)\n--\nfs/ext4/file.c-230- */\nfs/ext4/file.c:231:static bool ext4_dio_needs_zeroing(struct inode *inode, loff_t pos, loff_t len)\nfs/ext4/file.c-232-{\n--\nfs/ext4/file.c=490=static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,\n--\nfs/ext4/file.c-519-\tif (ext4_unaligned_io(inode, from, offset))\nfs/ext4/file.c:520:\t\tneeds_zeroing = ext4_dio_needs_zeroing(inode, offset, count);\nfs/ext4/file.c-521-\n"
}

gemini-3.1-pro-preview

null

null

							input: 8155
							output: 36
							thoughts: 95
						

Okay, here's my breakdown of what I'm looking at, from my expert perspective:

**Prioritizing Ext4 Write Path Functions**

Alright, let's get down to it. Given the need to analyze the ext4 write path, my mental checklist now zeroes in on specific key functions. I need to focus on these crucial pieces: `ext4_dio_needs_zeroing`, `ext4_buffered_write_iter`, `ext4_dio_write_checks`, and `ext4_dax_write_iter`. Of course, I need to understand how the iomap allocator, `ext4_iomap_alloc`, fits into this whole picture, given its central role. Time to dive into the code. My immediate target is `ext4_iomap_alloc`, and I'm heading directly to `fs/ext4/inode.c` to understand its implementation. It's time to see how the allocation process works in detail.

{
  "Expression": "ext4_iomap_alloc",
  "PathPrefix": "fs/ext4/inode.c"
}

{
  "Output": "fs/ext4/inode.c=3532=static int ext4_map_blocks_atomic_write_slow(handle_t *handle,\n--\nfs/ext4/inode.c-3621- *\nfs/ext4/inode.c:3622: * We first use m_flags passed to us by our caller (ext4_iomap_alloc()).\nfs/ext4/inode.c-3623- * We only call EXT4_GET_BLOCKS_ZERO in the slow path, when the underlying\n--\nfs/ext4/inode.c=3636=static int ext4_map_blocks_atomic_write(handle_t *handle, struct inode *inode,\n--\nfs/ext4/inode.c-3667-\nfs/ext4/inode.c:3668:static int ext4_iomap_alloc(struct inode *inode, struct ext4_map_blocks *map,\nfs/ext4/inode.c-3669-\t\t\t    unsigned int flags)\n--\nfs/ext4/inode.c=3776=static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,\n--\nfs/ext4/inode.c-3809-\t\t\t * copying the data, otherwise we do it after I/O so\nfs/ext4/inode.c:3810:\t\t\t * there's no need to call into ext4_iomap_alloc().\nfs/ext4/inode.c-3811-\t\t\t */\n--\nfs/ext4/inode.c-3824-\t\t}\nfs/ext4/inode.c:3825:\t\tret = ext4_iomap_alloc(inode, \u0026map, flags);\nfs/ext4/inode.c-3826-\t} else {\n"
}

gemini-3.1-pro-preview

null

null

							input: 8955
							output: 159
							thoughts: 357
						

**Fuzzing Strategy for ext4 I/O Modification**

Okay, so this patch is a definite functional change, altering the behavior of `ext4_iomap_alloc` to return `-EAGAIN` under the `IOMAP_NOWAIT` flag. That immediately flags this as something we need to subject to fuzzing.

My reasoning is straightforward: this patch touches core filesystem logic related to both direct I/O (DIO) and buffered I/O within ext4. Specifically, it seems to be dealing with cases involving unaligned DIO writes, partial block zeroing, *and* the addition of `NOWAIT` support in DAX and iomap allocation. These are all critical areas that, if mishandled, could lead to serious issues, so fuzzing them is a must. These are all definitely core routines within the filesystem, thus we want to fuzz this.

We've identified the key symbols to target: `ext4_dio_needs_zeroing`, `ext4_buffered_write_iter`, `ext4_dio_write_checks`, `ext4_dax_write_iter`, and `ext4_iomap_alloc`.

Now, the necessary kernel configurations are clear: `EXT4_FS` and `FS_DAX`. I've double-checked that `FS_DAX` is, in fact, relevant to `ext4_dax_write_iter`, which is good due diligence. And it appears that the other key functions, specifically `ext4_dio_needs_zeroing`, `ext4_buffered_write_iter`, `ext4_dio_write_checks`, and `ext4_iomap_alloc`, are not gated behind any specific configuration options. Thus, `EXT4_FS` and `FS_DAX` are sufficient. With those configurations, we should be able to trigger all the relevant logic and identify any potential vulnerabilities.

{
  "EnableConfigs": [
    "EXT4_FS",
    "FS_DAX"
  ],
  "FocusSymbols": [
    "ext4_dio_needs_zeroing",
    "ext4_buffered_write_iter",
    "ext4_dio_write_checks",
    "ext4_dax_write_iter",
    "ext4_iomap_alloc"
  ],
  "Reasoning": "The patch modifies ext4 direct I/O and buffered I/O logic, specifically handling unaligned DIO writes and partial block zeroing, as well as adding NOWAIT support in DAX and iomap allocation. These are reachable core filesystem logic changes that should be fuzzed.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "EXT4_FS",
    "FS_DAX"
  ],
  "FocusSymbols": [
    "ext4_dio_needs_zeroing",
    "ext4_buffered_write_iter",
    "ext4_dio_write_checks",
    "ext4_dax_write_iter",
    "ext4_iomap_alloc"
  ],
  "Reasoning": "The patch modifies ext4 direct I/O and buffered I/O logic, specifically handling unaligned DIO writes and partial block zeroing, as well as adding NOWAIT support in DAX and iomap allocation. These are reachable core filesystem logic changes that should be fuzzed.",
  "WorthFuzzing": true
}