io_uring: simplify the SQPOLL thread check when cancelling requests

In io_uring_try_cancel_requests, we check whether sq_data->thread ==
current to determine if the function is called by the SQPOLL thread to do
iopoll when IORING_SETUP_SQPOLL is set. This check can race with the SQPOLL
thread termination.

io_uring_cancel_generic is used in 2 places: io_uring_cancel_generic and
io_ring_exit_work. In io_uring_cancel_generic, we have the information
whether the current is SQPOLL thread already. And the SQPOLL thread never
reaches io_ring_exit_work.

So to avoid the racy check, this commit adds a boolean flag to
io_uring_try_cancel_requests to determine if the caller is SQPOLL thread.

Reported-by: [email protected]
Reported-by: Li Zetao <[email protected]>
Reviewed-by: Li Zetao <[email protected]>
Signed-off-by: Bui Quang Minh <[email protected]>
Reviewed-by: Pavel Begunkov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: minhbq-99

io_uring/io_uring.c

@@ -143,7 +143,8 @@ struct io_defer_entry {
 
 static bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
 					 struct io_uring_task *tctx,
-					 bool cancel_all);
+					 bool cancel_all,
+					 bool is_sqpoll_thread);
 
 static void io_queue_sqe(struct io_kiocb *req);
 
@@ -2869,7 +2870,8 @@ static __cold void io_ring_exit_work(struct work_struct *work)
 		if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
 			io_move_task_work_from_local(ctx);
 
-		while (io_uring_try_cancel_requests(ctx, NULL, true))
+		/* The SQPOLL thread never reaches this path */
+		while (io_uring_try_cancel_requests(ctx, NULL, true, false))
 			cond_resched();
 
 		if (ctx->sq_data) {
@@ -3037,7 +3039,8 @@ static __cold bool io_uring_try_cancel_iowq(struct io_ring_ctx *ctx)
 
 static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
 						struct io_uring_task *tctx,
-						bool cancel_all)
+						bool cancel_all,
+						bool is_sqpoll_thread)
 {
 	struct io_task_cancel cancel = { .tctx = tctx, .all = cancel_all, };
 	enum io_wq_cancel cret;
@@ -3067,7 +3070,7 @@ static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
 
 	/* SQPOLL thread does its own polling */
 	if ((!(ctx->flags & IORING_SETUP_SQPOLL) && cancel_all) ||
-	    (ctx->sq_data && ctx->sq_data->thread == current)) {
+	    is_sqpoll_thread) {
 		while (!wq_list_empty(&ctx->iopoll_list)) {
 			io_iopoll_try_reap_events(ctx);
 			ret = true;
@@ -3140,13 +3143,15 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
 					continue;
 				loop |= io_uring_try_cancel_requests(node->ctx,
 							current->io_uring,
-							cancel_all);
+							cancel_all,
+							false);
 			}
 		} else {
 			list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
 				loop |= io_uring_try_cancel_requests(ctx,
 								     current->io_uring,
-								     cancel_all);
+								     cancel_all,
+								     true);
 		}
 
 		if (loop) {