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

[Jingbo Xu]

On 7/17/26 9:58 PM, Miklos Szeredi wrote:
> 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?


Sure. Will send v2 soon.

-- 
Thanks,
Jingbo