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From: Pavel Begunkov <[email protected]>
To: Hao Xu <[email protected]>, Jens Axboe <[email protected]>
Cc: [email protected]
Subject: Re: Question about async_wake
Date: Wed, 8 Sep 2021 14:24:25 +0100	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

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

      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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