On 12/21/2011 03:30 PM, Williams, Dan J wrote:
> On Tue, Dec 20, 2011 at 10:48 PM, Tao Ma <tm@xxxxxx> wrote:
>> On 12/21/2011 02:36 PM, Meelis Roos wrote:
>>>>> - if (unlikely(tag >= bqt->max_depth)) {
>>>>> + if (WARN_ONCE(tag >= bqt->real_max_depth,
>>>>> + "%s: tag %d greater than tag map size: %d\n",
>>>>> + __func__, tag, bqt->real_max_depth)) {
>>>>> /*
>>>>> * This can happen after tag depth has been reduced.
>>>> Please also change the comments here since it should never happen in the
>>>> right workload.
>>>
>>> What do you mean by right workload? Normal workload?
>> yeah, so real_max_depth is the maximum depth we ever have. So in normal
>> case(shrinking queue depth is also a normal user case), we should never
>> arrive here. In another word, if tag >= real_max_depth, we should have a
>> bug in the kernel.
>
> So this is what Ed Nadolski suggested, just cut to the chase and do,
> the following. Seems like the comment is what got us into trouble in
> the first place.
>
> diff --git a/block/blk-tag.c b/block/blk-tag.c
> index e74d6d1..e297d9d7 100644
> --- a/block/blk-tag.c
> +++ b/block/blk-tag.c
> @@ -284,16 +284,7 @@ void blk_queue_end_tag(struct request_queue *q,
> struct request *rq)
> struct blk_queue_tag *bqt = q->queue_tags;
> int tag = rq->tag;
>
> - BUG_ON(tag == -1);
> -
> - if (unlikely(tag >= bqt->max_depth)) {
> - /*
> - * This can happen after tag depth has been reduced.
> - * But tag shouldn't be larger than real_max_depth.
> - */
> - WARN_ON(tag >= bqt->real_max_depth);
> - return;
> - }
> + BUG_ON(tag == -1 || tag > bqt->real_max_depth);
I guess tag = bqt->real_max_depth should also be a problem.
Thanks
Tao
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