From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Subject: Re: [PATCH 1/1] io_uring: fix missing mb() before waitqueue_active
Date: Wed, 8 Sep 2021 21:09:56 +0100 [thread overview]
Message-ID: <34219094-7e90-a665-2998-4658f3becdff@gmail.com> (raw)
In-Reply-To: <bd0b0727-d0ac-7f2a-323d-39411edbe45d@kernel.dk>
On 9/8/21 8:57 PM, Jens Axboe wrote:
> On 9/8/21 1:49 PM, Pavel Begunkov wrote:
>> In case of !SQPOLL, io_cqring_ev_posted_iopoll() doesn't provide a
>> memory barrier required by waitqueue_active(&ctx->poll_wait). There is
>> a wq_has_sleeper(), which does smb_mb() inside, but it's called only for
>> SQPOLL.
>
> We can probably get rid of the need to even do so by having the slow
> path (eg someone waiting on cq_wait or poll_wait) a bit more expensive,
> but this should do for now.
You have probably seen smp_mb__after_spin_unlock() trick [1], easy way
to get rid of it for !IOPOLL. Haven't figured it out for IOPOLL, though
[1] https://github.com/isilence/linux/commit/bb391b10d0555ba2d55aa8ee0a08dff8701a6a57
--
Pavel Begunkov
next prev parent reply other threads:[~2021-09-08 20:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-08 19:49 [PATCH 1/1] io_uring: fix missing mb() before waitqueue_active Pavel Begunkov
2021-09-08 19:57 ` Jens Axboe
2021-09-08 20:09 ` Pavel Begunkov [this message]
2021-09-08 20:15 ` Jens Axboe
2021-09-08 20:22 ` Pavel Begunkov
2021-09-08 20:24 ` Jens Axboe
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