[PATCH 5.10 59/63] io_uring: remove racy overflow list fast checks

Greg Kroah-Hartman
2021-01-04T16:05:56Z

From: Pavel Begunkov <asml.silence@gmail.com>

[ Upstream commit 9cd2be519d05ee78876d55e8e902b7125f78b74f ]

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: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/io_uring.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e28eedab5365f..1f798c5c4213e 100644
--- a/fs/io_uring.c
+++ b/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;
}

--
2.27.0