Re: [PATCH 2/2] io_uring: fix race between poll completion and cancel_hash insertion

[Pavel Begunkov <asml.silence@gmail.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