io_uring: limit {io|sq}poll submit locking scope

We don't need to take uring_lock for SQPOLL|IOPOLL to do
io_cqring_overflow_flush() when cq_overflow_list is empty, remove it
from the hot path.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -9154,10 +9154,13 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 	 */
 	ret = 0;
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
-		io_ring_submit_lock(ctx, (ctx->flags & IORING_SETUP_IOPOLL));
-		if (!list_empty_careful(&ctx->cq_overflow_list))
+		if (!list_empty_careful(&ctx->cq_overflow_list)) {
+			bool needs_lock = ctx->flags & IORING_SETUP_IOPOLL;
+
+			io_ring_submit_lock(ctx, needs_lock);
 			io_cqring_overflow_flush(ctx, false, NULL, NULL);
-		io_ring_submit_unlock(ctx, (ctx->flags & IORING_SETUP_IOPOLL));
+			io_ring_submit_unlock(ctx, needs_lock);
+		}
 		if (flags & IORING_ENTER_SQ_WAKEUP)
 			wake_up(&ctx->sq_data->wait);
 		if (flags & IORING_ENTER_SQ_WAIT)