On Thu, Jul 28, 2016 at 8:50 AM, Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
> [ adding linux-block ]
>
> On Wed, Jul 27, 2016 at 8:20 PM, Yi Zhang <yizhan-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>> Hello everyone
>>
>> Could you help check this issue, thanks.
>>
>> Steps I used:
>> 1. Reserve 4*8G of memory for pmem by add kernel parameter "memmap=8G!4G memmap=8G!12G memmap=8G!20G memmap=8G!28G"
>> 2. Execute below script
>> #!/bin/bash
>> pmem_btt_switch() {
>>         sector_size_list="512 520 528 4096 4104 4160 4224"
>>         for sector_size in $sector_size_list; do
>>                 ndctl create-namespace -f -e namespace${1}.0 --mode=sector -l $sector_size
>>                 ndctl create-namespace -f -e namespace${1}.0 --mode=raw
>>         done
>> }
>>
>> for i in 0 1 2 3; do
>>         pmem_btt_switch $i &
>> done
>
> Thanks for the report.  This looks like del_gendisk() frees the
> previous usage of the devt before the bdi is unregistered.  This
> appears to be a general problem with all block drivers, not just
> libnvdimm, since blk_cleanup_queue() is typically called after
> del_gendisk().  I.e. it will always be the case that the bdi
> registered with the devt allocated at add_disk() will still be alive
> when del_gendisk()->disk_release() frees the previous devt number.
>
> I *think* the path forward is to allow the bdi to hold a reference
> against the blk_alloc_devt() allocation until it is done with it.  Any
> other ideas on fixing this object lifetime problem?

Does the attached patch solve this for you?