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From: Pavel Begunkov <[email protected]>
To: Jens Axboe <[email protected]>, [email protected]
Cc: [email protected], Joseph Qi <[email protected]>
Subject: Re: [PATCH 5.11] io_uring: fix wqe->lock/completion_lock deadlock
Date: Tue, 26 Jan 2021 23:37:18 +0000	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <9c4f7eb623ae774f3f17afbc1702749480ee19be.1611703952.git.asml.silence@gmail.com>

On 26/01/2021 23:35, Pavel Begunkov wrote:
> Joseph reports following deadlock:
> 
> CPU0:
> ...
> io_kill_linked_timeout  // &ctx->completion_lock
> io_commit_cqring
> __io_queue_deferred
> __io_queue_async_work
> io_wq_enqueue
> io_wqe_enqueue  // &wqe->lock
> 
> CPU1:
> ...
> __io_uring_files_cancel
> io_wq_cancel_cb
> io_wqe_cancel_pending_work  // &wqe->lock
> io_cancel_task_cb  // &ctx->completion_lock
> 
> Only __io_queue_deferred() calls queue_async_work() while holding
> ctx->completion_lock, enqueue drained requests via io_req_task_queue()
> instead.

Joseph, can you try it out? would much appreciate

> 
> Cc: [email protected] # 5.9+
> Reported-by: Joseph Qi <[email protected]>
> Signed-off-by: Pavel Begunkov <[email protected]>
> ---
>  fs/io_uring.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index bb0270eeb8cb..c218deaf73a9 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1026,6 +1026,7 @@ static int io_setup_async_rw(struct io_kiocb *req, const struct iovec *iovec,
>  			     const struct iovec *fast_iov,
>  			     struct iov_iter *iter, bool force);
>  static void io_req_drop_files(struct io_kiocb *req);
> +static void io_req_task_queue(struct io_kiocb *req);
>  
>  static struct kmem_cache *req_cachep;
>  
> @@ -1634,18 +1635,11 @@ static void __io_queue_deferred(struct io_ring_ctx *ctx)
>  	do {
>  		struct io_defer_entry *de = list_first_entry(&ctx->defer_list,
>  						struct io_defer_entry, list);
> -		struct io_kiocb *link;
>  
>  		if (req_need_defer(de->req, de->seq))
>  			break;
>  		list_del_init(&de->list);
> -		/* punt-init is done before queueing for defer */
> -		link = __io_queue_async_work(de->req);
> -		if (link) {
> -			__io_queue_linked_timeout(link);
> -			/* drop submission reference */
> -			io_put_req_deferred(link, 1);
> -		}
> +		io_req_task_queue(de->req);
>  		kfree(de);
>  	} while (!list_empty(&ctx->defer_list));
>  }
> 

-- 
Pavel Begunkov

  reply	other threads:[~2021-01-27  4:45 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-26 23:35 [PATCH 5.11] io_uring: fix wqe->lock/completion_lock deadlock Pavel Begunkov
2021-01-26 23:37 ` Pavel Begunkov [this message]
2021-01-27  1:52 ` Joseph Qi
2021-01-27  2:40   ` Jens Axboe
2021-01-27  9:21   ` Pavel Begunkov

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