Re: [PATCH] blktrace: Protect q->blk_trace with RCU

[Ming Lei <tom.leiming@xxxxxxxxx>]

On Tue, Mar 3, 2020 at 8:37 PM Cengiz Can <cengiz@xxxxxxxxxx> wrote:
>
> Added a reassignment into the NULL check block to fix the issue.
>
> Fixes: c780e86dd48 ("blktrace: Protect q->blk_trace with RCU")
>
> Signed-off-by: Cengiz Can <cengiz@xxxxxxxxxx>
> ---
>  kernel/trace/blktrace.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 4560878f0bac..29ea88f10b87 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -1896,8 +1896,10 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
>         }
>
>         ret = 0;
> -       if (bt == NULL)
> +       if (bt == NULL) {
>                 ret = blk_trace_setup_queue(q, bdev);
> +               bt = q->blk_trace;

I'd suggest to use the following line for avoiding RCU warning:

   bt = rcu_dereference_protected(q->blk_trace,
                                       lockdep_is_held(&q->blk_trace_mutex));

Otherwise, the patch looks fine for me:

Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>

Thanks,
Ming Lei