io_uring: make sqpoll wakeup possible with getevents

commit b2a9eadab85730935f5a6fe19f3f61faaaced601 upstream.

The way the logic is setup in io_uring_enter() means that you can't wake
up the SQ poller thread while at the same time waiting (or polling) for
completions afterwards. There's no reason for that to be the case.
Reported-by: NLewis Baker <lbaker@fb.com>
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

fs/io_uring.c

@@ -3356,15 +3356,12 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 	 * Just return the requested submit count, and wake the thread if
 	 * we were asked to.
 	 */
+	ret = 0;
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
 		if (flags & IORING_ENTER_SQ_WAKEUP)
 			wake_up(&ctx->sqo_wait);
 		submitted = to_submit;
-		goto out_ctx;
-	}
-
-	ret = 0;
-	if (to_submit) {
+	} else if (to_submit) {
 		bool block_for_last = false;
 
 		to_submit = min(to_submit, ctx->sq_entries);
@@ -3394,7 +3391,6 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 		}
 	}
 
-out_ctx:
 	io_ring_drop_ctx_refs(ctx, 1);
 out_fput:
 	fdput(f);