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

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Feb 06, 2020 at 03:28:12PM +0100, Jan Kara wrote:

> @@ -1844,18 +1896,18 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
>  	}
>  
>  	ret = 0;
> -	if (q->blk_trace == NULL)
> +	if (bt == NULL)
>  		ret = blk_trace_setup_queue(q, bdev);
>  
>  	if (ret == 0) {
>  		if (attr == &dev_attr_act_mask)
> -			q->blk_trace->act_mask = value;
> +			bt->act_mask = value;

You've likely seen this already, but Coverity complains that "bt" may
be a NULL pointer here, since we checked it for NULL above.

  CID 1460458:  Null pointer dereferences  (FORWARD_NULL)

>  		else if (attr == &dev_attr_pid)
> -			q->blk_trace->pid = value;
> +			bt->pid = value;
>  		else if (attr == &dev_attr_start_lba)
> -			q->blk_trace->start_lba = value;
> +			bt->start_lba = value;
>  		else if (attr == &dev_attr_end_lba)
> -			q->blk_trace->end_lba = value;
> +			bt->end_lba = value;
>  	}
>  
>  out_unlock_bdev:
>