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

[Miklos Szeredi]

On Mon, 6 Jul 2026 at 10:29, Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx>

Can you please add a Fixes: tag and possibly Cc: stable@... if appropriate?

Thanks,
Miklos