[PATCH 3/3] blk-mq: avoid access hctx->tags->cpumask before allocation

[AceLan Kao]

This patch comes from here, we only need the first commit in that series.
https://lkml.org/lkml/2015/7/18/98

2015-09-23 21:57 GMT+08:00 Chris J Arges <chris.j.arges at canonical.com>:
> Which tree did this patch come from? I don't see it in mainline.
> If it isn't in mainline, it would also be good to explain if this needed
> in Wily/4.2 as well.
>
> --chris
>
> On 09/23/2015 02:56 AM, AceLan Kao wrote:
>> From: Akinobu Mita <akinobu.mita at gmail.com>
>>
>> BugLink: http://bugs.launchpad.net/bugs/1498778
>>
>> When unmapped hw queue is remapped after CPU topology is changed,
>> hctx->tags->cpumask is set before hctx->tags is allocated in
>> blk_mq_map_swqueue().
>>
>> In order to fix this null pointer dereference, hctx->tags must be
>> allocated before configuring hctx->tags->cpumask.
>>
>> Fixes: f26cdc8536 ("blk-mq: Shared tag enhancements")
>> Signed-off-by: Akinobu Mita <akinobu.mita at gmail.com>
>> Cc: Keith Busch <keith.busch at intel.com>
>> Cc: Jens Axboe <axboe at kernel.dk>
>> Cc: Ming Lei <tom.leiming at gmail.com>
>>
>> Signed-off-by: AceLan Kao <acelan.kao at canonical.com>
>> ---
>>  block/blk-mq.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 9ea3230..74f7087 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -1783,7 +1783,6 @@ static void blk_mq_map_swqueue(struct request_queue *q)
>>
>>               hctx = q->mq_ops->map_queue(q, i);
>>               cpumask_set_cpu(i, hctx->cpumask);
>> -             cpumask_set_cpu(i, hctx->tags->cpumask);
>>               ctx->index_hw = hctx->nr_ctx;
>>               hctx->ctxs[hctx->nr_ctx++] = ctx;
>>       }
>> @@ -1814,6 +1813,14 @@ static void blk_mq_map_swqueue(struct request_queue *q)
>>               hctx->next_cpu = cpumask_first(hctx->cpumask);
>>               hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
>>       }
>> +
>> +     queue_for_each_ctx(q, ctx, i) {
>> +             if (!cpu_online(i))
>> +                     continue;
>> +
>> +             hctx = q->mq_ops->map_queue(q, i);
>> +             cpumask_set_cpu(i, hctx->tags->cpumask);
>> +     }
>>  }
>>
>>  static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set)
>>
>
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