BUG: NULL pointer at IP: blk_mq_map_swqueue+0xbc/0x200 on 4.15.0-rc2

[Jens Axboe]

On 12/12/17 2:16 AM, Ming Lei wrote:
> On Tue, Dec 12, 2017 at 12:35:02AM -0800, Christoph Hellwig wrote:
>> On Mon, Dec 11, 2017 at 11:58:45AM +0800, Ming Lei wrote:
>>> As we talked offline, this IP points to cpumask_set_cpu(), seems this
>>> case may happen when one CPU isn't mapped to any hw queue, could you test
>>> the following patch to see if it helps your issue?
>>
>> This looks odd as mq_map should be pre-zeroed.  If it isn't we have
>> a few more problems..
> 
> This happens in case of updating nr_hw_queue, for example, when the
> number becomes 5 from 12, then the table has to be zeroed for avoiding
> obsolete mapping if one CPU isn't mapped to any hw queue.

Do you have a proper complete patch for this?

-- 
Jens Axboe