linux-kernel - [PATCH AUTOSEL 5.10 26/31] io_uring: remove racy overflow list fast checks

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Date:   Wed, 30 Dec 2020 08:03:08 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Pavel Begunkov <asml.silence@...il.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 26/31] io_uring: remove racy overflow list fast checks

From: Pavel Begunkov <asml.silence@...il.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@...il.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.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 86dac2b2e2763..4b3dbe588d111 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1632,8 +1632,6 @@ 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;
@@ -6548,8 +6546,7 @@ 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