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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, Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: [PATCH 2/2] io_uring: fix race between poll completion and cancel_hash insertion
Date: Wed, 15 Sep 2021 11:12:57 +0100	[thread overview]
Message-ID: <b4d71d4e-187d-c96e-2122-e50362c8ead0@gmail.com> (raw)
In-Reply-To: <20210912162345.51651-3-haoxu@linux.alibaba.com>

On 9/12/21 5:23 PM, Hao Xu wrote:
> If poll arming and poll completion runs parallelly, there maybe races.
> For instance, run io_poll_add in iowq and io_poll_task_func in original
> context, then:
>              iowq                          original context
>   io_poll_add
>     vfs_poll
>      (interruption happens
>       tw queued to original
>       context)                              io_poll_task_func
>                                               generate cqe
>                                               del from cancel_hash[]
>     if !poll.done
>       insert to cancel_hash[]
> 
> The entry left in cancel_hash[], similar case for fast poll.
> Fix it by set poll.done = true when del from cancel_hash[].
> 
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
> 
> Didn't find the exact commit to add Fixes: for..
> 
>  fs/io_uring.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index c16f6be3d46b..988679e5063f 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5118,10 +5118,8 @@ static bool __io_poll_complete(struct io_kiocb *req, __poll_t mask)
>  	}
>  	if (req->poll.events & EPOLLONESHOT)
>  		flags = 0;
> -	if (!io_cqring_fill_event(ctx, req->user_data, error, flags)) {
> -		req->poll.done = true;
> +	if (!io_cqring_fill_event(ctx, req->user_data, error, flags))
>  		flags = 0;
> -	}
>  	if (flags & IORING_CQE_F_MORE)
>  		ctx->cq_extra++;
>  
> @@ -5152,6 +5150,7 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
>  		if (done) {
>  			io_poll_remove_double(req);
>  			hash_del(&req->hash_node);
> +			req->poll.done = true;
>  		} else {
>  			req->result = 0;
>  			add_wait_queue(req->poll.head, &req->poll.wait);
> @@ -5289,6 +5288,7 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked)
>  
>  	hash_del(&req->hash_node);
>  	io_poll_remove_double(req);
> +	req->poll.done = true;

Only poll request has req->poll. E.g. it overwrites parts of req->rw.kiocb,
I guess .ki_complete in particular.

struct async_poll *apoll = req->apoll;
apoll->poll.done = true;


>  	spin_unlock(&ctx->completion_lock);
>  
>  	if (!READ_ONCE(apoll->poll.canceled))
> 

-- 
Pavel Begunkov

  parent reply	other threads:[~2021-09-15 10:13 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-12 16:23 [PATCH 0/2] poll fixes Hao Xu
2021-09-12 16:23 ` [PATCH 1/2] io_uring: fix tw list mess-up by adding tw while it's already in tw list Hao Xu
2021-09-15  9:44   ` Pavel Begunkov
2021-09-15 10:48     ` Hao Xu
2021-09-26  9:48       ` Hao Xu
2021-09-29 11:16         ` Pavel Begunkov
2021-09-12 16:23 ` [PATCH 2/2] io_uring: fix race between poll completion and cancel_hash insertion Hao Xu
2021-09-15  9:50   ` Pavel Begunkov
2021-09-15 10:49     ` Hao Xu
2021-09-15 10:12   ` Pavel Begunkov [this message]
2021-09-15 10:50     ` Hao Xu

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