Re: [PATCH 3/4] io_uring: fix poll_rewait racing for ->canceled

[Pavel Begunkov <asml.silence@gmail.com>]

On 08/04/2021 01:54, Pavel Begunkov wrote:
> poll->canceled may be set from different contexts, even async, so
> io_poll_rewait() should be prepared that it can change and not read it
> twice.

Please disregard this one, apparently it's not a bug and will get in
my way letter. Other 3 are fine.

> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  fs/io_uring.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index de5822350345..376d9c875dc2 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -4897,15 +4897,16 @@ static bool io_poll_rewait(struct io_kiocb *req, struct io_poll_iocb *poll)
>  	__acquires(&req->ctx->completion_lock)
>  {
>  	struct io_ring_ctx *ctx = req->ctx;
> +	bool canceled = READ_ONCE(poll->canceled);
>  
> -	if (!req->result && !READ_ONCE(poll->canceled)) {
> +	if (!req->result && !canceled) {
>  		struct poll_table_struct pt = { ._key = poll->events };
>  
>  		req->result = vfs_poll(req->file, &pt) & poll->events;
>  	}
>  
>  	spin_lock_irq(&ctx->completion_lock);
> -	if (!req->result && !READ_ONCE(poll->canceled)) {
> +	if (!req->result && !canceled) {
>  		add_wait_queue(poll->head, &poll->wait);
>  		return true;
>  	}
> 

-- 
Pavel Begunkov