io_uring: remove racy overflow list fast checks

stable inclusion
from stable-5.10.5
commit c7b04d27c9107fbc0d22dee67316f8584439df35
bugzilla: 46931

--------------------------------

[ Upstream commit 9cd2be51 ]

list_empty_careful() is not racy only if some conditions are met, i.e.
no re-adds after del_init. io_cqring_overflow_flush() does list_move(),
so it's actually racy.

Remove those checks, we have ->cq_check_overflow for the fast path.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

fs/io_uring.c

@@ -1636,8 +1636,6 @@ static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
 	LIST_HEAD(list);
 
 	if (!force) {
-		if (list_empty_careful(&ctx->cq_overflow_list))
-			return true;
 		if ((ctx->cached_cq_tail - READ_ONCE(rings->cq.head) ==
 		    rings->cq_ring_entries))
 			return false;
@@ -6579,8 +6577,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
 
 	/* if we have a backlog and couldn't flush it all, return BUSY */
 	if (test_bit(0, &ctx->sq_check_overflow)) {
-		if (!list_empty(&ctx->cq_overflow_list) &&
-		    !io_cqring_overflow_flush(ctx, false, NULL, NULL))
+		if (!io_cqring_overflow_flush(ctx, false, NULL, NULL))
 			return -EBUSY;
 	}