io_uring: set -EINTR directly when a signal wakes up in io_cqring_wait

We didn't use -ERESTARTSYS to tell the application layer to restart the
system call, but instead return -EINTR. we can set -EINTR directly when
wakeup by the signal, which can help us save an assignment operation and
comparison operation.
Reviewed-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NJackie Liu <liuyun01@kylinos.cn>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2976,7 +2976,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 		.to_wait	= min_events,
 	};
 	struct io_rings *rings = ctx->rings;
-	int ret;
+	int ret = 0;
 
 	if (io_cqring_events(rings) >= min_events)
 		return 0;
@@ -2994,7 +2994,6 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 			return ret;
 	}
 
-	ret = 0;
 	iowq.nr_timeouts = atomic_read(&ctx->cq_timeouts);
 	trace_io_uring_cqring_wait(ctx, min_events);
 	do {
@@ -3004,15 +3003,13 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 			break;
 		schedule();
 		if (signal_pending(current)) {
-			ret = -ERESTARTSYS;
+			ret = -EINTR;
 			break;
 		}
 	} while (1);
 	finish_wait(&ctx->wait, &iowq.wq);
 
-	restore_saved_sigmask_unless(ret == -ERESTARTSYS);
-	if (ret == -ERESTARTSYS)
-		ret = -EINTR;
+	restore_saved_sigmask_unless(ret == -EINTR);
 
 	return READ_ONCE(rings->cq.head) == READ_ONCE(rings->cq.tail) ? ret : 0;
 }