io_uring: fix poll requests leaking second poll entries

For pure poll requests, it doesn't remove the second poll wait entry
when it's done, neither after vfs_poll() or in the poll completion
handler. We should remove the second poll wait entry.
And we use io_poll_remove_double() rather than io_poll_remove_waitqs()
since the latter has some redundant logic.

Fixes: 88e41cf ("io_uring: add multishot mode for IORING_OP_POLL_ADD")
Cc: stable@vger.kernel.org # 5.13+
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
Link: https://lore.kernel.org/r/20210728030322.12307-1-haoxu@linux.alibaba.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -4939,7 +4939,6 @@ 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)) {
-		io_poll_remove_waitqs(req);
 		req->poll.done = true;
 		flags = 0;
 	}
@@ -4962,6 +4961,7 @@ static void io_poll_task_func(struct io_kiocb *req)
 
 		done = io_poll_complete(req, req->result);
 		if (done) {
+			io_poll_remove_double(req);
 			hash_del(&req->hash_node);
 		} else {
 			req->result = 0;
@@ -5149,7 +5149,7 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
 		ipt->error = -EINVAL;
 
 	spin_lock_irq(&ctx->completion_lock);
-	if (ipt->error)
+	if (ipt->error || (mask && (poll->events & EPOLLONESHOT)))
 		io_poll_remove_double(req);
 	if (likely(poll->head)) {
 		spin_lock(&poll->head->lock);
@@ -5221,7 +5221,6 @@ static int io_arm_poll_handler(struct io_kiocb *req)
 	ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
 					io_async_wake);
 	if (ret || ipt.error) {
-		io_poll_remove_double(req);
 		spin_unlock_irq(&ctx->completion_lock);
 		if (ret)
 			return IO_APOLL_READY;