Re: [PATCH 3/6] io_uring: fix racy overflow count reporting

[Jens Axboe <axboe@kernel.dk>]

On 7/30/20 9:43 AM, Pavel Begunkov wrote:
> 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>
> ---
>  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 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);

Torn writes? Not sure I see what the issue here, can you expand?

-- 
Jens Axboe