io_uring: improve task exit timeout cancellations

Don't spin trying to cancel timeouts that are reachable but not
cancellable, e.g. already executing.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/ab8a7440a60bbdf69ae514f672ad050e43dd1b03.1655684496.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/timeout.c

@@ -49,7 +49,7 @@ static inline void io_put_req(struct io_kiocb *req)
 	}
 }
 
-static void io_kill_timeout(struct io_kiocb *req, int status)
+static bool io_kill_timeout(struct io_kiocb *req, int status)
 	__must_hold(&req->ctx->completion_lock)
 	__must_hold(&req->ctx->timeout_lock)
 {
@@ -64,7 +64,9 @@ static void io_kill_timeout(struct io_kiocb *req, int status)
 			atomic_read(&req->ctx->cq_timeouts) + 1);
 		list_del_init(&timeout->list);
 		io_req_tw_post_queue(req, status, 0);
+		return true;
 	}
+	return false;
 }
 
 __cold void io_flush_timeouts(struct io_ring_ctx *ctx)
@@ -620,10 +622,9 @@ __cold bool io_kill_timeouts(struct io_ring_ctx *ctx, struct task_struct *tsk,
 	list_for_each_entry_safe(timeout, tmp, &ctx->timeout_list, list) {
 		struct io_kiocb *req = cmd_to_io_kiocb(timeout);
 
-		if (io_match_task(req, tsk, cancel_all)) {
-			io_kill_timeout(req, -ECANCELED);
+		if (io_match_task(req, tsk, cancel_all) &&
+		    io_kill_timeout(req, -ECANCELED))
 			canceled++;
-		}
 	}
 	spin_unlock_irq(&ctx->timeout_lock);
 	io_commit_cqring(ctx);