From: Pavel Begunkov <asml.silence@gmail.com>
Date: Thu, 30 Jul 2020 15:43:47 +0000 (+0300)
Subject: io_uring: fix racy overflow count reporting
X-Git-Tag: v5.9-rc1~212^2~6
X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=b2bd1cf99f3e7c8fbf12ea07af2c6998e1209e25;p=tomoyo%2Ftomoyo-test1.git

io_uring: fix racy overflow count reporting

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@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 11f4ab87e08f..6e2322525da6 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7847,10 +7847,9 @@ 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