Re: [PATCH] mm/memremap: Fix reuse of pgmap instances with internal references

[Jeff Moyer <jmoyer@redhat.com>]

Dan Williams <dan.j.williams@intel.com> writes:

> On Mon, Aug 12, 2019 at 8:51 AM Jeff Moyer <jmoyer@redhat.com> wrote:
>>
>> Dan Williams <dan.j.williams@intel.com> writes:
>>
>> > Currently, attempts to shutdown and re-enable a device-dax instance
>> > trigger:
>>
>> What does "shutdown and re-enable" translate to?  If I disable and
>> re-enable a device-dax namespace, I don't see this behavior.
>
> I was not seeing this either until I made sure I was in 'bus" device model mode.
>
> # cat /etc/modprobe.d/daxctl.conf
> blacklist dax_pmem_compat
> alias nd:t7* dax_pmem
>
> # make TESTS="daxctl-devices.sh" check -j 40 2>out
>
> # dmesg | grep WARN.*devm
> [  225.588651] WARNING: CPU: 10 PID: 9103 at mm/memremap.c:211
> devm_memremap_pages+0x234/0x850
> [  225.679828] WARNING: CPU: 10 PID: 9103 at mm/memremap.c:211
> devm_memremap_pages+0x234/0x850

Ah, you see this when reconfiguring the device.  So, the lifetime of the
pgmap is tied to the character device, which doesn't get torn down.  The
fix looks good to me, and tests out fine.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>