From: Pavel Begunkov <asml.silence@gmail.com>
To: Hao Xu <haoxu@linux.alibaba.com>, Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org
Subject: Re: Question about async_wake
Date: Wed, 8 Sep 2021 14:24:25 +0100 [thread overview]
Message-ID: <dd547d1e-2132-ebc6-dd36-7cce4e870675@gmail.com> (raw)
In-Reply-To: <e65f822b-419d-4555-21e8-54e11bf294b2@linux.alibaba.com>
On 9/8/21 12:18 PM, Hao Xu wrote:
> Hi Jens, Pavel,
> I have a question about _async_wake(), would there be cases like
> this:
> async_cancel/poll_remove interrupt
> spin_lock_irq()
> list del poll->wait_entry event happens but irq disabled
> so interrupt delays
> spin_unlock_irq()
> generate cqe
> async_wake() called and
> generate cqe
wake_up*() looks for queued callbacks under that same spin, so it
won't find that cancelled entry and so won't call io_async_wake().
There might be other similar (or not) problematic cases, though.
> If it exists, there may be multiple -ECANCELED cqes for one req,
> we may do something like this to avoid it:
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 30d959416eba..7822b2f9e890 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5023,9 +5023,12 @@ static int __io_async_wake(struct io_kiocb *req, struct io_poll_iocb *poll,
> if (mask && !(mask & poll->events))
> return 0;
>
> - trace_io_uring_task_add(req->ctx, req->opcode, req->user_data, mask);
> + if (list_empty(&poll->wait.entry))
> + return 0;
> + else
> + list_del_init(&poll->wait.entry);
>
> - list_del_init(&poll->wait.entry);
> + trace_io_uring_task_add(req->ctx, req->opcode, req->user_data, mask);
>
> req->result = mask;
> req->io_task_work.func = func;
--
Pavel Begunkov
prev parent reply other threads:[~2021-09-08 13:25 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-08 11:18 Question about async_wake Hao Xu
2021-09-08 13:24 ` Pavel Begunkov [this message]
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