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From: Pavel Begunkov <[email protected]>
To: Hillf Danton <[email protected]>
Cc: syzbot <[email protected]>,
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected]
Subject: Re: INFO: task hung in __io_uring_files_cancel
Date: Mon, 23 Nov 2020 20:25:29 +0000	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 23/11/2020 07:34, Hillf Danton wrote:
[...]
> After staring the report and 311daef8013a a bit more, it seems that we
> can have a simpler fix without the help of wakeup. It is implemented
> by busy waiting until there is no more request in flight found.

I think it's better not. It doesn't happen instantly, so may take a
lot of spinning in some cases. Moreover, I don't want an unkillable
task eating up all CPU if this hangs again (eg because of some other
case).

And, I'd love to keep it working similarly to __io_uring_task_cancel()
to not think twice about all corner cases.

> 
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -6077,13 +6077,10 @@ static int io_req_defer(struct io_kiocb
>  static void io_req_drop_files(struct io_kiocb *req)
>  {
>  	struct io_ring_ctx *ctx = req->ctx;
> -	struct io_uring_task *tctx = req->task->io_uring;
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&ctx->inflight_lock, flags);
>  	list_del(&req->inflight_entry);
> -	if (atomic_read(&tctx->in_idle))
> -		wake_up(&tctx->wait);
>  	spin_unlock_irqrestore(&ctx->inflight_lock, flags);
>  	req->flags &= ~REQ_F_INFLIGHT;
>  	put_files_struct(req->work.identity->files);
> @@ -8706,7 +8703,6 @@ static void io_uring_cancel_files(struct
>  	while (!list_empty_careful(&ctx->inflight_list)) {
>  		struct io_task_cancel cancel = { .task = task, .files = NULL, };
>  		struct io_kiocb *req;
> -		DEFINE_WAIT(wait);
>  		bool found = false;
>  
>  		spin_lock_irq(&ctx->inflight_lock);
> @@ -8718,9 +8714,6 @@ static void io_uring_cancel_files(struct
>  			found = true;
>  			break;
>  		}
> -		if (found)
> -			prepare_to_wait(&task->io_uring->wait, &wait,
> -					TASK_UNINTERRUPTIBLE);
>  		spin_unlock_irq(&ctx->inflight_lock);
>  
>  		/* We need to keep going until we don't find a matching req */
> @@ -8733,7 +8726,6 @@ static void io_uring_cancel_files(struct
>  		/* cancellations _may_ trigger task work */
>  		io_run_task_work();
>  		schedule();
> -		finish_wait(&task->io_uring->wait, &wait);
>  	}
>  }
>  
> 

-- 
Pavel Begunkov

  parent reply	other threads:[~2020-11-23 20:29 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-21 22:35 INFO: task hung in __io_uring_files_cancel syzbot
     [not found] ` <[email protected]>
2020-11-22  3:32   ` Pavel Begunkov
     [not found]   ` <[email protected]>
2020-11-22 15:57     ` Pavel Begunkov
     [not found]     ` <[email protected]>
2020-11-23 20:25       ` Pavel Begunkov [this message]
2020-11-24  9:39 ` syzbot

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