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

[Ming Lei]

On Fri, Jan 05, 2018 at 09:39:48AM -0700, Jens Axboe wrote:
> 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?

Please see the latest version:

	https://marc.info/?l=linux-block&m=151522728023803&w=2

Thanks,
Ming