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

[Cengiz Can <cengiz@kernel.wtf>]

On March 5, 2020 04:51:51 Ming Lei <tom.leiming@gmail.com> wrote:

> 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:

Thank you.

Please kindly see v2.

>
> Reviewed-by: Ming Lei <ming.lei@redhat.com>
>
> Thanks,
> Ming Lei