Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap

[Alexander Duyck]

On 10/8/2018 3:00 PM, Dan Williams wrote:
> On Mon, Oct 8, 2018 at 2:48 PM Alexander Duyck
> <alexander.h.duyck@xxxxxxxxxxxxxxx> wrote:
> > On 10/8/2018 2:01 PM, Dan Williams wrote:
> > > On Tue, Sep 25, 2018 at 1:29 PM Alexander Duyck
> > > <alexander.h.duyck@xxxxxxxxxxxxxxx> wrote:
> > > > The ZONE_DEVICE pages were being initialized in two locations. One was with
> > > > the memory_hotplug lock held and another was outside of that lock. The
> > > > problem with this is that it was nearly doubling the memory initialization
> > > > time. Instead of doing this twice, once while holding a global lock and
> > > > once without, I am opting to defer the initialization to the one outside of
> > > > the lock. This allows us to avoid serializing the overhead for memory init
> > > > and we can instead focus on per-node init times.
> > > >
> > > > One issue I encountered is that devm_memremap_pages and
> > > > hmm_devmmem_pages_create were initializing only the pgmap field the same
> > > > way. One wasn't initializing hmm_data, and the other was initializing it to
> > > > a poison value. Since this is something that is exposed to the driver in
> > > > the case of hmm I am opting for a third option and just initializing
> > > > hmm_data to 0 since this is going to be exposed to unknown third party
> > > > drivers.
> > > >
> > > > Reviewed-by: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>
> > > > Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> > > > ---
> > > >
> > > > v4: Moved moved memmap_init_zone_device to below memmmap_init_zone to avoid
> > > >       merge conflicts with other changes in the kernel.
> > > > v5: No change
> > >
> > > This patch appears to cause a regression in the "create.sh" unit test
> > > in the ndctl test suite.
> >
> > So all you had to do is run the create.sh script to see the issue? I
> > just want to confirm there isn't any additional information needed
> > before I try chasing this down.
>
>  From the ndctl source tree run:
>
>      make -j TESTS="create.sh" check
>
> ...the readme has some more setup instructions:
> https://github.com/pmem/ndctl/blob/master/README.md
>
> 0day has sometimes run this test suite automatically, but we need to
> get that more robust because setting up this environment is a bit of a
> hoop to jump through with the need to setup the nfit_test module.
>
> > > I tried to reproduce on -next with:
> > >
> > > 2302f5ee215e mm: defer ZONE_DEVICE page initialization to the point
> > > where we init pgmap
> > >
> > > ...but -next does not even boot for me at that commit.
> >
> > What version of -next? There are a couple of patches probably needed
> > depending on which version you are trying to boot.
>
> Today's -next, but backed up to that above commit. I was also seeing
> CONFIG_DEBUG_LIST spamming the logs, and a crash in the crypto layer.
>
> > > Here is a warning signature that proceeds a hang with this patch
> > > applied against v4.19-rc6:
> > >
> > > percpu ref (blk_queue_usage_counter_release) <= 0 (-1530626) after
> > > switching to atomic
> > > WARNING: CPU: 24 PID: 7346 at lib/percpu-refcount.c:155
> > > percpu_ref_switch_to_atomic_rcu+0x1f7/0x200
> > > CPU: 24 PID: 7346 Comm: modprobe Tainted: G           OE     4.19.0-rc6+ #2458
> > > [..]
> > > RIP: 0010:percpu_ref_switch_to_atomic_rcu+0x1f7/0x200
> > > [..]
> > > Call Trace:
> > >    <IRQ>
> > >    ? percpu_ref_reinit+0x140/0x140
> > >    rcu_process_callbacks+0x273/0x880
> > >    __do_softirq+0xd2/0x428
> > >    irq_exit+0xf6/0x100
> > >    smp_apic_timer_interrupt+0xa2/0x220
> > >    apic_timer_interrupt+0xf/0x20
> > >    </IRQ>
> > > RIP: 0010:lock_acquire+0xb8/0x1a0
> > > [..]
> > >    ? __put_page+0x55/0x150
> > >    ? __put_page+0x55/0x150
> > >    __put_page+0x83/0x150
> > >    ? __put_page+0x55/0x150
> > >    devm_memremap_pages_release+0x194/0x250
> > >    release_nodes+0x17c/0x2c0
> > >    device_release_driver_internal+0x1a2/0x250
> > >    driver_detach+0x3a/0x70
> > >    bus_remove_driver+0x58/0xd0
> > >    __x64_sys_delete_module+0x13f/0x200
> > >    ? trace_hardirqs_off_thunk+0x1a/0x1c
> > >    do_syscall_64+0x60/0x210
> > >    entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > So it looks like we are tearing down memory when this is triggered. Do
> > we know if this is at the end of the test or if this is running in
> > parallel with anything?
>
> Should not be running in parallel with anything this test is
> performing a series of namespace setup and teardown events.
>
> Wait, where did the call to "percpu_ref_get()" go? I think that's the bug.

I have a reproduction on my system now as well. I should have a patch 
ready to go for it in the next hour or so.

Thanks.

- Alex