Re: [PATCH v3 2/8] PM / Domains: Handle safely genpd_syscore_switch() call on non-genpd device

From: Geert Uytterhoeven
Date: Tue Jul 04 2017 - 14:19:55 EST

Hi Krzysztof,

On Tue, Jul 4, 2017 at 8:10 PM, Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote:
> On Tue, Jul 04, 2017 at 03:01:15PM +0200, Geert Uytterhoeven wrote:
>> On Wed, Jun 28, 2017 at 4:56 PM, Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote:
>> > genpd_syscore_switch() had two problems:
>> > 1. It silently assumed that device, it is being called for, belongs to
>> > generic power domain and used container_of() on its power domain
>> > pointer. Such assumption might not be true always.
>> >
>> > 2. It iterated over list of generic power domains without holding
>> > gpd_list_lock mutex thus list could have been modified in the same
>> > time.
>> >
>> > Usage of genpd_lookup_dev() solves both problems as it is safe a call
>> > for non-generic power domains and uses mutex when iterating.
>> >
>> > Reported-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
>> > Signed-off-by: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
>> > Acked-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
>> This is commit 8b55e55ee44356d6 in pm/linux-next, also part of the pull
>> request "[GIT PULL] Power management updates for v4.13-rc1".
>> > Not tested on real hardware.
>> This causes the following BUG during s2ram on all my Renesas arm32 boards,
>> where the system timer is an IRQ safe device:
>> PM: Syncing filesystems ... done.
>> PM: Preparing system for sleep (mem)
>> Freezing user space processes ... (elapsed 0.001 seconds) done.
>> OOM killer disabled.
>> Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
>> PM: Suspending system (mem)
>> PM: suspend of devices complete after 122.841 msecs
>> PM: suspend devices took 0.130 seconds
>> PM: late suspend of devices complete after 2.682 msecs
>> PM: noirq suspend of devices complete after 29.951 msecs
>> Disabling non-boot CPUs ...
>> BUG: sleeping function called from invalid context at kernel/locking/mutex.c:238
> Thanks for report!
> Damn it, although I couldn't find this in the code, but I was fearing
> that this ends up in atomic section. That would kind of explain why
> mutex was not there [1].
> Anyway, the buggy code was there already. Instead of "sleeping in atomic
> section" there was no locking at all... In this context this was
> probably safe because it was executed *after* disabling non-boot CPUs
> but then the function cannot be called in other contexts.
> I am not sure I will be capable of developing the proper fix as I do not
> have the hardware and I do not know all stuff happening in sh suspend.
> Probably reverting this and living with non-locked path would be the
> safest choice.
> [1]

AFAIU, all syscore stuff runs in atomic context.

Don't worry, you're not the only one.
This bug report was almost 100% the same as an earlier one for a patch
from Ulf ;-)
(cfr. "[RESEND PATCH 0/2] PM / Domains: Fix asynchronous execution of
*noirq() callbacks")



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds