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

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By any chance will the following patch be able to get rid of
the warning ?

index 4560878f0bac..889555910555 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1895,9 +1895,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct 
device *dev,
                 goto out_unlock_bdev;
         }

-       ret = 0;
-       if (bt == NULL)
-               ret = blk_trace_setup_queue(q, bdev);
+       ret = bt == NULL ? blk_trace_setup_queue(q, bdev) : 0;

         if (ret == 0) {
                 if (attr == &dev_attr_act_mask)

On 03/02/2020 12:41 PM, Bjorn Helgaas wrote:
> 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:
>>
>





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