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

On Tue, Mar 3, 2020 at 8:37 PM Cengiz Can cengiz@kernel.wtf 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@kernel.wtf

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@redhat.com

Thanks, Ming Lei