Re: [PATCH v3 1/2] io_uring: cmpxchg for poll arm refs release

[Jens Axboe <axboe@kernel.dk>]

On 11/25/22 6:51 AM, Pavel Begunkov wrote:
> On 11/20/22 16:57, Pavel Begunkov wrote:
>> Replace atomically substracting the ownership reference at the end of
>> arming a poll with a cmpxchg. We try to release ownership by setting 0
>> assuming that poll_refs didn't change while we were arming. If it did
>> change, we keep the ownership and use it to queue a tw, which is fully
>> capable to process all events and (even tolerates spurious wake ups).
>>
>> It's a bit more elegant as we reduce races b/w setting the cancellation
>> flag and getting refs with this release, and with that we don't have to
>> worry about any kinds of underflows. It's not the fastest path for
>> polling. The performance difference b/w cmpxchg and atomic dec is
>> usually negligible and it's not the fastest path.
> 
> Jens, can you add a couple of tags? Not a fix but the second patch
> depends on it but applies cleanly even without 1/2, which may mess
> things up.
> 
> Cc: stable@vger.kernel.org
> Fixes: aa43477b04025 ("io_uring: poll rework")

Sure, done.

-- 
Jens Axboe