On Tue, Jul 04, 2017 at 08:19:47PM +0200, Geert Uytterhoeven wrote: > 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] https://patchwork.kernel.org/patch/9778903/ > > AFAIU, all syscore stuff runs in atomic context. Indeed... The confusing part is that this code is syscore only from the name, it is not hooked in to syscore_ops. Although going by call chain (through sh clocksource drivers) we end up in timekeeping_suspend() which is a syscore op. I wonder whether it would be useful - after reverting my commit - to add an assert (which is a stronger API requirement than only documentation "may only be called during the system core (syscore) suspend") like: WARN_ON(num_online_cpus() > 1)); as without mutexes this should not be executed with more than one online CPU. Best regards, Krzysztof > > 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") > > 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
