[PATCH] fuse: don't bump attr_version for async direct read completion

[PATCH] fuse: don't bump attr_version for async direct read completion

[Jingbo Xu]

The attr_version counter should only be incremented when cached
attributes are actually modified (as documented in commit 1fb69e781729
("fuse: fix race between getattr and write")).  Async direct reads do not
modify any cached inode attributes (size, mtime, ctime), so bumping
attr_version in fuse_aio_complete() for reads is incorrect.

This unconditional bump causes a livelock when auto_inval_data is
enabled together with writeback_cache: fuse_cache_read_iter() issues a
FUSE_GETATTR before every read, but by the time the response arrives,
an async DIO read completion has already incremented fi->attr_version
past the snapshot taken before the request.  The GETATTR result is then
discarded (attr_version race), fi->i_time is never refreshed, and every
subsequent read triggers yet another GETATTR -- creating an infinite
loop of useless round-trips.

Fix this by only bumping attr_version for write completions, consistent
with the synchronous DIO write path (fuse_write_update_attr) and the
cached write path.

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
---
 fs/fuse/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index ceada75310b8..c41287e8bc15 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -688,7 +688,7 @@ static void fuse_aio_complete(struct fuse_io_priv *io, int err, ssize_t pos)
 		struct address_space *mapping = io->iocb->ki_filp->f_mapping;
 		ssize_t res = fuse_get_res_by_io(io);
 
-		if (res >= 0) {
+		if (res >= 0 && io->write) {
 			struct fuse_conn *fc = get_fuse_conn(inode);
 			struct fuse_inode *fi = get_fuse_inode(inode);
 
-- 
2.19.1.6.gb485710b

Re: [PATCH] fuse: don't bump attr_version for async direct read completion

[Horst Birthelmer]

On Mon, Jul 06, 2026 at 04:29:31PM +0800, Jingbo Xu wrote:
> The attr_version counter should only be incremented when cached
> attributes are actually modified (as documented in commit 1fb69e781729
> ("fuse: fix race between getattr and write")).  Async direct reads do not
> modify any cached inode attributes (size, mtime, ctime), so bumping
> attr_version in fuse_aio_complete() for reads is incorrect.
> 
> This unconditional bump causes a livelock when auto_inval_data is
> enabled together with writeback_cache: fuse_cache_read_iter() issues a
> FUSE_GETATTR before every read, but by the time the response arrives,
> an async DIO read completion has already incremented fi->attr_version
> past the snapshot taken before the request.  The GETATTR result is then
> discarded (attr_version race), fi->i_time is never refreshed, and every
> subsequent read triggers yet another GETATTR -- creating an infinite
> loop of useless round-trips.
> 
> Fix this by only bumping attr_version for write completions, consistent
> with the synchronous DIO write path (fuse_write_update_attr) and the
> cached write path.
> 
> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> ---
>  fs/fuse/file.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index ceada75310b8..c41287e8bc15 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -688,7 +688,7 @@ static void fuse_aio_complete(struct fuse_io_priv *io, int err, ssize_t pos)
>  		struct address_space *mapping = io->iocb->ki_filp->f_mapping;
>  		ssize_t res = fuse_get_res_by_io(io);
>  
> -		if (res >= 0) {
> +		if (res >= 0 && io->write) {
>  			struct fuse_conn *fc = get_fuse_conn(inode);
>  			struct fuse_inode *fi = get_fuse_inode(inode);
>  
> -- 
> 2.19.1.6.gb485710b
> 
> 
LGTM

Reviewed-by: Horst Birthelmer <hbirthelmer@ddn.com>