Hi,
On 9/9/2021 5:19 PM, Ming Lei wrote:
> Hello Hou,
>
> On Thu, Sep 09, 2021 at 05:00:54PM +0800, Hou Tao wrote:
>> According to commit 4412efecf7fd ("Revert "blk-mq: remove code for
>> dealing with remapping queue""), for some devices queue hctx may not
>> being mapped, and tagset->tags[hctx_idx] will be released and be NULL.
>>
>> If an IO scheduler is used on these devices, blk_mq_clear_rq_mapping()
>> will be called for all hctxs in blk_mq_sched_free_requests() during
>> scheduler switch, and these will be oops. So checking the existence of
>> tags[hctx_idx] before going on in blk_mq_clear_rq_mapping().
> unmapped hctx should be caused by blk_mq_update_nr_hw_queues() only,
> but scheduler tags is updated there too, so not sure it is one real
> issue, did you observe such kernel panic? any kernel log?
Not a real issue, just find the potential "problem" during code review.
But is the case below possible ?
There is an unmapped hctx and a freed tags[hctx_idx] after
blk_mq_update_nr_hw_queues(), and IO scheduler is used. When
switching IO scheduler to none, the previous schedule tag
on each hctx will be freed in blk_mq_sched_free_requests().
blk_mq_sched_free_requests() will call blk_mq_free_rqs(), and
blk_mq_free_rqs() will access the NULLed tags[hctx_idx].
Regards,
Tao
>
> Thanks,
> Ming
>
> .
