iomap: fix zero padding data issue in concurrent append writes changed ioend accounting so that io_size tracks only valid data within EOF. This trims io_size when a writeback range extends past end_pos: ioend->io_size += map_len; if (ioend->io_offset + ioend->io_size > end_pos) ioend->io_size = end_pos - ioend->io_offset; However, if end_pos ends up below ioend->io_offset, the subtraction becomes negative and is stored in size_t io_size, causing an unsigned wrap to a huge value. This can happen when writeback continues past byte-level EOF up to a block-aligned range, or when a concurrent truncate shrinks the file after end_pos was sampled in iomap_writeback_handle_eof(). A wrapped io_size can mislead append detection and corrupt completion-time size handling, since filesystem end_io paths consume io_size for decisions such as on-disk EOF updates and unwritten/COW completion ranges. Fix this by clamping io_size to zero when EOF has moved to or before the ioend start offset. This preserves the original intent of trimming io_size to valid in-EOF data while avoiding the underflow. Fixes: 51d20d1dacbe ("iomap: fix zero padding data issue in concurrent append writes") Suggested-by: Christoph Hellwig Signed-off-by: Morduan Zang --- Changes in v2: - Adopt Christoph's suggested condition ordering for readability - No runtime reproducer yet; still working on a test setup v1: https://lore.kernel.org/all/863D407CB3ECEB04+20260618053820.506635-1-zhangdandan@uniontech.com/ --- fs/iomap/ioend.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c index acf3cf98b23a..2d5611f6cc57 100644 --- a/fs/iomap/ioend.c +++ b/fs/iomap/ioend.c @@ -297,8 +297,12 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio, * appending writes. */ ioend->io_size += map_len; - if (ioend->io_offset + ioend->io_size > end_pos) - ioend->io_size = end_pos - ioend->io_offset; + if (ioend->io_offset + ioend->io_size > end_pos) { + if (ioend->io_offset >= end_pos) + ioend->io_size = 0; + else + ioend->io_size = end_pos - ioend->io_offset; + } wbc_account_cgroup_owner(wpc->wbc, folio, map_len); return map_len; -- 2.50.1