Re: [PATCH 2/2] FUSE: fix congested state leak on aborted connections

[Miklos Szeredi]

On Tue, Feb 6, 2018 at 5:25 PM, Jan Kara <jack@xxxxxxx> wrote:
> On Fri 02-02-18 09:54:14, Tejun Heo wrote:
>> If a connection gets aborted while congested, FUSE can leave
>> nr_wb_congested[] stuck until reboot causing wait_iff_congested() to
>> wait spuriously which can lead to severe performance degradation.
>>
>> The leak is caused by gating congestion state clearing with
>> fc->connected test in request_end().  This was added way back in 2009
>> by 26c3679101db ("fuse: destroy bdi on umount").  While the commit
>> description doesn't explain why the test was added, it most likely was
>> to avoid dereferencing bdi after it got destroyed.
>>
>> Since then, bdi lifetime rules have changed many times and now we're
>> always guaranteed to have access to the bdi while the superblock is
>> alive (fc->sb).
>>
>> Drop fc->connected conditional to avoid leaking congestion states.
>>
>> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
>> Reported-by: Joshua Miller <joshmiller@xxxxxx>
>> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
>> Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
>> Cc: Jan Kara <jack@xxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx
>
> Yeah, this should be fine AFAICT but my knowledge of FUSE is very cursory.
> Anyway:
>
> Acked-by: Jan Kara <jack@xxxxxxx>

Can't say I fully understand how the global "is any bdi congested"
state is used in direct reclaim, but the patch is an obvious
improvement, so applied.

Thanks,
Miklos