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

[Krzysztof Kozlowski]

On Tue, Jul 04, 2017 at 03:01:15PM +0200, Geert Uytterhoeven wrote:
> Hi Krzysztof, Rafael,
> 
> 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

Hi,

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] https://patchwork.kernel.org/patch/9778903/

Best regards,
Krzysztof


> in_atomic(): 0, irqs_disabled(): 128, pid: 1730, name: s2ram
> CPU: 0 PID: 1730 Comm: s2ram Not tainted
> 4.12.0-koelsch-07061-g810fee9afeba15ef #3592
> Hardware name: Generic R8A7791 (Flattened Device Tree)
> [<c020e9f4>] (unwind_backtrace) from [<c020a484>] (show_stack+0x10/0x14)
> [<c020a484>] (show_stack) from [<c04017e8>] (dump_stack+0x7c/0x9c)
> [<c04017e8>] (dump_stack) from [<c0240284>] (___might_sleep+0x124/0x160)
> [<c0240284>] (___might_sleep) from [<c0717cfc>] (mutex_lock+0x18/0x60)
> [<c0717cfc>] (mutex_lock) from [<c04de11c>] (genpd_lookup_dev+0x38/0x94)
> [<c04de11c>] (genpd_lookup_dev) from [<c04dfd34>]
> (pm_genpd_syscore_poweroff+0x8/0x2c)
> [<c04dfd34>] (pm_genpd_syscore_poweroff) from [<c05fcb70>]
> (sh_cmt_clock_event_suspend+0x18/0x28)
> [<c05fcb70>] (sh_cmt_clock_event_suspend) from [<c027f174>]
> (clockevents_suspend+0x40/0x54)
> [<c027f174>] (clockevents_suspend) from [<c02762d8>]
> (timekeeping_suspend+0x23c/0x278)
> [<c02762d8>] (timekeeping_suspend) from [<c04ce028>]
> (syscore_suspend+0x88/0x138)
> [<c04ce028>] (syscore_suspend) from [<c025d740>]
> (suspend_devices_and_enter+0x308/0x4fc)
> [<c025d740>] (suspend_devices_and_enter) from [<c025db5c>]
> (pm_suspend+0x228/0x280)
> [<c025db5c>] (pm_suspend) from [<c025c6b8>] (state_store+0xac/0xcc)
> [<c025c6b8>] (state_store) from [<c0342f9c>] (kernfs_fop_write+0x170/0x1b0)
> [<c0342f9c>] (kernfs_fop_write) from [<c02e47dc>] (__vfs_write+0x20/0x108)
> [<c02e47dc>] (__vfs_write) from [<c02e5b80>] (vfs_write+0xb8/0x144)
> [<c02e5b80>] (vfs_write) from [<c02e6804>] (SyS_write+0x40/0x80)
> [<c02e6804>] (SyS_write) from [<c0206c40>] (ret_fast_syscall+0x0/0x34)
> 
> Reverting the commit fixes the issue.
> 
> > ---
> >  drivers/base/power/domain.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> > index 01e31d9f6c94..d31a4434b8b3 100644
> > --- a/drivers/base/power/domain.c
> > +++ b/drivers/base/power/domain.c
> > @@ -1098,8 +1098,8 @@ static void genpd_syscore_switch(struct device *dev, bool suspend)
> >  {
> >         struct generic_pm_domain *genpd;
> >
> > -       genpd = dev_to_genpd(dev);
> > -       if (!pm_genpd_present(genpd))
> > +       genpd = genpd_lookup_dev(dev);
> > +       if (!genpd)
> >                 return;
> >
> >         if (suspend) {
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> 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