iomap: fix error handling regressions

Assisted-by LLM

---
 fs/iomap/ioend.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

fs/iomap/ioend.c +9 -1

index 7bbbb417f9152..32ae292a84cbe 100644
@@ -246,8 +246,16 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
 new_ioend:
 		if (ioend) {
 			error = wpc->ops->writeback_submit(wpc, 0);
-			if (error)
+			if (error) {
+				/*
+				 * ->writeback_submit() completed the ioend
+				 * with an error, so drop the stale context;
+				 * iomap_writepages() would otherwise submit
+				 * it a second time.
+				 */
+				wpc->wb_ctx = NULL;
 				return error;
+			}
 		}
 		wpc->wb_ctx = ioend = iomap_alloc_ioend(wpc, pos, ioend_flags);
 	}

Signature · 1 line

2.53.0

Andrea Parri

author

2026-09-28 08:48 UTC #2 lore raw

PATCH v3 2/4 xfs: add an error tag to inject a ->writeback_submit() failure

The only in-tree way for xfs_writeback_submit() to fail is a failing xfs_reflink_convert_cow(), which requires a shared (reflinked) CoW extent. There was previously no way to exercise that failure path from userspace, which made it hard to write an xfstest for it, e.g. for "iomap: don't resubmit an ioend after ->writeback_submit() failed".

Add XFS_ERRTAG_WB_COW_CONVERT_ERROR to force xfs_reflink_convert_cow() to fail with -EIO, so that ->writeback_submit() failure and its callers' error handling can be exercised with error injection alone, without needing a corrupted or racy COW fork.

Reviewed-by Darrick J. Wong <[email protected]>

Assisted-by LLM

---
 fs/xfs/libxfs/xfs_errortag.h | 6 ++++--
 fs/xfs/xfs_reflink.c         | 5 +++++
 2 files changed, 9 insertions(+), 2 deletions(-)

fs/xfs/libxfs/xfs_errortag.h +4 -2

index 6de207fed2d89..a1955b7773e1f 100644
@@ -75,7 +75,8 @@
 #define XFS_ERRTAG_METAFILE_RESV_CRITICAL		45
 #define XFS_ERRTAG_FORCE_ZERO_RANGE			46
 #define XFS_ERRTAG_ZONE_RESET				47
-#define XFS_ERRTAG_MAX					48
+#define XFS_ERRTAG_WB_COW_CONVERT_ERROR			48
+#define XFS_ERRTAG_MAX					49
 
 /*
  * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.

@@ -137,7 +138,8 @@ XFS_ERRTAG(WRITE_DELAY_MS,	write_delay_ms,		3000) \
 XFS_ERRTAG(EXCHMAPS_FINISH_ONE,	exchmaps_finish_one,	1) \
 XFS_ERRTAG(METAFILE_RESV_CRITICAL, metafile_resv_crit,	4) \
 XFS_ERRTAG(FORCE_ZERO_RANGE,	force_zero_range,	4) \
-XFS_ERRTAG(ZONE_RESET,		zone_reset,		1)
+XFS_ERRTAG(ZONE_RESET,		zone_reset,		1) \
+XFS_ERRTAG(WB_COW_CONVERT_ERROR, wb_cow_convert_error,	1)
 #endif /* XFS_ERRTAG */
 
 #endif /* __XFS_ERRORTAG_H_ */

fs/xfs/xfs_reflink.c +5 -0

index 4801361366359..104542b10d9e0 100644
@@ -34,6 +34,8 @@
 #include "xfs_rtalloc.h"
 #include "xfs_rtgroup.h"
 #include "xfs_metafile.h"
+#include "xfs_errortag.h"
+#include "xfs_error.h"
 
 /*
  * Copy on Write of Shared Blocks

@@ -346,6 +348,9 @@ xfs_reflink_convert_cow(
 
 	ASSERT(count != 0);
 
+	if (XFS_TEST_ERROR(mp, XFS_ERRTAG_WB_COW_CONVERT_ERROR))
+		return -EIO;
+
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 	error = xfs_reflink_convert_cow_locked(ip, offset_fsb, count_fsb);
 	xfs_iunlock(ip, XFS_ILOCK_EXCL);

Signature · 1 line

2.53.0

Andrea Parri

author

2026-09-28 08:48 UTC #3 lore raw

PATCH v3 3/4 iomap: don't lose a fiemap iteration error when emitting the last extent

iomap_fiemap() emits extents one behind: iomap_fiemap_iter() flushes the previous extent and remembers the current one, and the remembered extent is written with FIEMAP_EXTENT_LAST after the iteration loop.

That final flush overwrites ret, so when ->iomap_begin() fails partway through the iteration the error is replaced by the result of iomap_to_fiemap() (zero on success) and iomap_fiemap() returns success with a truncated extent list whose last entry is wrongly marked as the last extent in the file. The pre-iomap_iter code returned the error from inside the loop, before flushing the pending extent.

Check for the iteration error before flushing the pending extent, so that real errors are propagated and only a successful iteration emits the final FIEMAP_EXTENT_LAST extent. -ENOENT (no mapping) is still not an error, and the pending extent is still emitted in that case.

Fixes 7892386d3571 ("iomap: switch iomap_fiemap to use iomap_iter")

Cc <[email protected]> # v5.15

Reviewed-by Brian Foster <[email protected]>

Reviewed-by Darrick J. Wong <[email protected]>

Assisted-by LLM

---
 fs/iomap/fiemap.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

fs/iomap/fiemap.c +4 -4

index d11dadff82865..54b824b7edb5c 100644
@@ -76,15 +76,15 @@ int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fi,
 	while ((ret = iomap_iter(&iter, ops)) > 0)
 		iter.status = iomap_fiemap_iter(&iter, fi, &prev);
 
+	/* inode with no (attribute) mapping will give ENOENT */
+	if (ret < 0 && ret != -ENOENT)
+		return ret;
+
 	if (prev.type != IOMAP_HOLE) {
 		ret = iomap_to_fiemap(fi, &prev, FIEMAP_EXTENT_LAST);
 		if (ret < 0)
 			return ret;
 	}
-
-	/* inode with no (attribute) mapping will give ENOENT */
-	if (ret < 0 && ret != -ENOENT)
-		return ret;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(iomap_fiemap);

Signature · 1 line

2.53.0

Andrea Parri

author

2026-09-28 08:48 UTC #4 lore raw

PATCH v3 4/4 iomap: don't lose a failed direct I/O bio's error when zeroing the tail

iomap_dio_bio_iter() falls through to the sub-block tail zeroing when the data bio submission fails, so that the rest of the block is still zeroed and stale data is not exposed. The zeroing result was assigned to ret, which overwrote the submission error with the successful zeroing result (zero) and the failed write was reported as success.

iomap_dio_zero() can only return an error from a can't-happen WARN_ON_ONCE() (nr_vecs exceeding BIO_MAX_VECS, which the existing comment there says "shall never be reached" for any in-tree filesystem), so it isn't a real runtime failure worth reporting to userspace, let alone one worth losing the actual submission error for. Make iomap_dio_zero() return void and drop the error handling at both call sites instead of threading the result through a separate variable.

Fixes 10553a91652d ("iomap: fix iomap_dio_zero() for fs bs > system page size")

Cc <[email protected]> # v6.12

Reviewed-by Darrick J. Wong <[email protected]>

Reviewed-by Pankaj Raghav <[email protected]>

Assisted-by LLM

---
 fs/iomap/direct-io.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

fs/iomap/direct-io.c +5 ~~-11~~

index 8b4039d16ce89..7f1e85f95a469 100644
@@ -296,7 +296,7 @@ u32 iomap_finish_ioend_direct(struct iomap_ioend *ioend)
 	return vec_count;
 }
 
-static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
+static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 		loff_t pos, unsigned len)
 {
 	struct inode *inode = file_inode(dio->iocb->ki_filp);

@@ -305,14 +305,14 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 	int nr_vecs = max(1, i_blocksize(inode) / folio_size(zero_folio));
 
 	if (!len)
-		return 0;
+		return;
 
 	/*
 	 * This limit shall never be reached as most filesystems have a
 	 * maximum blocksize of 64k.
 	 */
 	if (WARN_ON_ONCE(nr_vecs > BIO_MAX_VECS))
-		return -EINVAL;
+		return;
 
 	bio = iomap_dio_alloc_bio(iter, dio, nr_vecs,
 				  REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);

@@ -328,8 +328,6 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 		len -= io_len;
 	}
 	iomap_dio_submit_bio(iter, dio, bio, pos);
-
-	return 0;
 }
 
 static ssize_t iomap_dio_bio_iter_one(struct iomap_iter *iter,

@@ -541,10 +539,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
 	if (need_zeroout) {
 		/* zero out from the start of the block to the write offset */
 		pad = pos & (fs_block_size - 1);
-
-		ret = iomap_dio_zero(iter, dio, pos - pad, pad);
-		if (ret)
-			goto out;
+		iomap_dio_zero(iter, dio, pos - pad, pad);
 	}
 
 	do {

@@ -582,8 +577,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
 		/* zero out from the end of the write to the end of the block */
 		pad = pos & (fs_block_size - 1);
 		if (pad)
-			ret = iomap_dio_zero(iter, dio, pos,
-					     fs_block_size - pad);
+			iomap_dio_zero(iter, dio, pos, fs_block_size - pad);
 	}
 out:
 	/* Undo iter limitation to current extent */

Signature · 1 line

2.53.0

Christoph Hellwig

Reviewed-by on v3 4/4

2026-09-28 08:51 UTC #5 lore raw

Re: [PATCH v3 4/4] iomap: don't lose a failed direct I/O bio's error when zeroing the tail

Looks good:

Christian Brauner

maintainer Applied

2026-10-12 14:25 UTC #6 lore raw