On Tue, Jul 4, 2017 at 8:36 PM, Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote: > 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. Or maybe WARN_ON_ONCE(!in_atomic())? I'm queuing up a revert of the $subject commit. Thanks, Rafael
