[PATCH v2 0/3] fs: drain in-flight DIO before buffered write fallback

[PATCH v2 0/3] fs: drain in-flight DIO before buffered write fallback

[Jiale Yao]

An asynchronous direct write can remain in flight after its submitting
thread releases the inode lock.  If another direct write falls back to
buffered I/O in the meantime, the buffered write can dirty page cache
before the first write completes post-I/O invalidation.  The invalidation
then finds dirty pages, emits a page cache invalidation failure warning,
and records -EIO in the mapping error sequence.  A later fsync() returns
-EIO.

Commit 15cdefd0c0522f9d5e12d947fa04f4c11649b699 ("ext4: drain
in-flight DIO before buffered write fallback") fixed this race in ext4.
The same ordering is missing from the buffered fallback paths in ext2,
NTFS, and exFAT.

This series adds inode_dio_wait() before each fallback dirties page cache.
Each patch fixes one filesystem and remains independently buildable.  The
NTFS patch also avoids entering the blocking fallback for IOCB_NOWAIT
requests: it returns -EAGAIN if DIO made no progress and preserves a
positive result after a partial direct write.

A reproducer using concurrent AIO direct writes and buffered fallback
triggered the following warning on all three filesystems and made a
subsequent fsync() return -EIO:

  Page cache invalidation failure on direct I/O.  Possible data corruption
  due to collision with buffered I/O!

Changes in v2:
- Handle IOCB_NOWAIT before the potentially blocking NTFS fallback,
  returning -EAGAIN before any bytes are written and preserving a positive
  short-write result otherwise, as requested in review.

Jiale Yao (3):
  ext2: drain in-flight DIO before buffered write fallback
  ntfs: drain in-flight DIO before buffered write fallback
  exfat: drain in-flight DIO before buffered write fallback

 fs/exfat/file.c |  6 ++++++
 fs/ext2/file.c  |  7 +++++++
 fs/ntfs/file.c  | 13 +++++++++++++
 3 files changed, 26 insertions(+)

-- 
2.34.1

[PATCH v2 1/3] ext2: drain in-flight DIO before buffered write fallback

[Jiale Yao]

An asynchronous direct write can remain in flight after the inode lock is
released.  If another direct write falls back to buffered I/O while the
first write is still pending, generic_perform_write() can dirty pages
before the first write completes its post-I/O page cache invalidation.
The invalidation then finds dirty pages, reports a page cache invalidation
failure, and records -EIO in the mapping error sequence.  A later fsync()
therefore returns -EIO.

Commit 15cdefd0c0522f9d5e12d947fa04f4c11649b699 ("ext4: drain
in-flight DIO before buffered write fallback") fixed the same race in
ext4.  Ext2 has an equivalent fallback after iomap_dio_rw() returns
-ENOTBLK or a short write, but does not drain other in-flight DIO before
dirtying the page cache.

Wait for in-flight DIO before calling generic_perform_write() in the
fallback path.

A reproducer using concurrent AIO direct writes and buffered fallback
triggered the following warning and made a subsequent fsync() return
-EIO:

  Page cache invalidation failure on direct I/O.  Possible data corruption
  due to collision with buffered I/O!

Fixes: fb5de4358e1a ("ext2: Move direct-io to use iomap")
Link: https://lore.kernel.org/r/20260629113827.4074335-3-libaokun@linux.alibaba.com
Signed-off-by: Jiale Yao <yaojiale02@163.com>
---
 fs/ext2/file.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index b9020df7d89e..67fe423c3828 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -135,6 +135,13 @@ static ssize_t ext2_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		int ret2;
 
 		iocb->ki_flags &= ~IOCB_DIRECT;
+
+		/*
+		 * 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);
+
 		pos = iocb->ki_pos;
 		status = generic_perform_write(iocb, from);
 		if (unlikely(status < 0)) {
-- 
2.34.1

Re: [PATCH v2 1/3] ext2: drain in-flight DIO before buffered write fallback

[sashiko-bot]

> An asynchronous direct write can remain in flight after the inode lock is
> released.  If another direct write falls back to buffered I/O while the
> first write is still pending, generic_perform_write() can dirty pages
> before the first write completes its post-I/O page cache invalidation.
> The invalidation then finds dirty pages, reports a page cache invalidation
> failure, and records -EIO in the mapping error sequence.  A later fsync()
> therefore returns -EIO.
> 
> Commit 15cdefd0c0522f9d5e12d947fa04f4c11649b699 ("ext4: drain
> in-flight DIO before buffered write fallback") fixed the same race in
> ext4.  Ext2 has an equivalent fallback after iomap_dio_rw() returns
> -ENOTBLK or a short write, but does not drain other in-flight DIO before
> dirtying the page cache.
> 
> Wait for in-flight DIO before calling generic_perform_write() in the
> fallback path.
> 
> A reproducer using concurrent AIO direct writes and buffered fallback
> triggered the following warning and made a subsequent fsync() return
> -EIO:
> 
>   Page cache invalidation failure on direct I/O.  Possible data corruption
>   due to collision with buffered I/O!
> 
> Fixes: fb5de4358e1a ("ext2: Move direct-io to use iomap")
> Link: https://lore.kernel.org/r/20260629113827.4074335-3-libaokun@linux.alibaba.com
> Signed-off-by: Jiale Yao <yaojiale02@163.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260926072612.3022680-1-yaojiale02@163.com?part=1

Re: [PATCH v2 1/3] ext2: drain in-flight DIO before buffered write fallback

[Jan Kara]

On Sat 26-09-26 15:26:10, Jiale Yao wrote:
> An asynchronous direct write can remain in flight after the inode lock is
> released.  If another direct write falls back to buffered I/O while the
> first write is still pending, generic_perform_write() can dirty pages
> before the first write completes its post-I/O page cache invalidation.
> The invalidation then finds dirty pages, reports a page cache invalidation
> failure, and records -EIO in the mapping error sequence.  A later fsync()
> therefore returns -EIO.
> 
> Commit 15cdefd0c0522f9d5e12d947fa04f4c11649b699 ("ext4: drain
> in-flight DIO before buffered write fallback") fixed the same race in
> ext4.  Ext2 has an equivalent fallback after iomap_dio_rw() returns
> -ENOTBLK or a short write, but does not drain other in-flight DIO before
> dirtying the page cache.
> 
> Wait for in-flight DIO before calling generic_perform_write() in the
> fallback path.
> 
> A reproducer using concurrent AIO direct writes and buffered fallback
> triggered the following warning and made a subsequent fsync() return
> -EIO:
> 
>   Page cache invalidation failure on direct I/O.  Possible data corruption
>   due to collision with buffered I/O!
> 
> Fixes: fb5de4358e1a ("ext2: Move direct-io to use iomap")
> Link: https://lore.kernel.org/r/20260629113827.4074335-3-libaokun@linux.alibaba.com
> Signed-off-by: Jiale Yao <yaojiale02@163.com>

This patch is already merged in my tree. You can drop it from the series.

								Honza

> ---
>  fs/ext2/file.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index b9020df7d89e..67fe423c3828 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -135,6 +135,13 @@ static ssize_t ext2_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  		int ret2;
>  
>  		iocb->ki_flags &= ~IOCB_DIRECT;
> +
> +		/*
> +		 * 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);
> +
>  		pos = iocb->ki_pos;
>  		status = generic_perform_write(iocb, from);
>  		if (unlikely(status < 0)) {
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR