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[].
Sounds like a valid concern. And the code looks good, but one
of two patches crashed the kernel somewhere in io_read().
./232c93d07b74-test
will be retesting
> Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
> ---
>
> Didn't find the exact commit to add Fixes: for..
That's ok. Maybe you can find which kernel versions are
affected? So we can add stable and specify where it should
be backported? E.g.
Cc: stable@xxxxxxxxxxxxxxx # 5.12+
> 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;
> spin_unlock(&ctx->completion_lock);
>
> if (!READ_ONCE(apoll->poll.canceled))
>
--
Pavel Begunkov
