linux-kernel - [PATCH AUTOSEL 5.8 61/64] io_uring: fix racy overflow count reporting

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Message-Id: <20200810190859.3793319-61-sashal@kernel.org>
Date:   Mon, 10 Aug 2020 15:08:56 -0400
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>,
        io-uring@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH AUTOSEL 5.8 61/64] io_uring: fix racy overflow count reporting

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

[ Upstream commit b2bd1cf99f3e7c8fbf12ea07af2c6998e1209e25 ]

All ->cq_overflow modifications should be under completion_lock,
otherwise it can report a wrong number to the userspace. Fix it in
io_uring_cancel_files().

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 | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index acd98df1f7d44..73f5e0a9bf2bd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7529,10 +7529,9 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 				clear_bit(0, &ctx->cq_check_overflow);
 				ctx->rings->sq_flags &= ~IORING_SQ_CQ_OVERFLOW;
 			}
-			spin_unlock_irq(&ctx->completion_lock);
-
 			WRITE_ONCE(ctx->rings->cq_overflow,
 				atomic_inc_return(&ctx->cached_cq_overflow));
+			spin_unlock_irq(&ctx->completion_lock);
 
 			/*
 			 * Put inflight ref and overflow ref. If that's
-- 
2.25.1