On Mon, Jan 12, 2015 at 03:55:05PM +0000, Sören Brinkmann wrote: > On Mon, 2015-01-12 at 03:43PM +0000, Lorenzo Pieralisi wrote: > > Hi Rafael, Soren, > > > > On Sun, Jan 11, 2015 at 11:20:36PM +0000, Rafael J. Wysocki wrote: > > > On Friday, January 09, 2015 01:50:59 PM Sören Brinkmann wrote: > > > > On Sat, 2014-11-08 at 03:56PM -0800, Sören Brinkmann wrote: > > > > > Hi Rafael, > > > > > > > > > > On Thu, 2014-11-06 at 01:33AM +0100, Rafael J. Wysocki wrote: > > > > > > On Thursday, October 02, 2014 09:01:15 AM Sören Brinkmann wrote: > > > > > > > Hi Rafael, > > > > > > > > > > > > Hi, > > > > > > > > > > > > Sorry for the huge delay. > > > > > > > > > > > > > On Tue, 2014-09-23 at 01:01AM +0200, Rafael J. Wysocki wrote: > > > > > > > > On Monday, September 22, 2014 10:07:03 AM Soren Brinkmann wrote: > > > > > > > > > On platforms that do not power off during suspend, > > > > > > > > > successfully entering > > > > > > > > > suspend races with timers. > > > > > > > > > > > > > > > > > > The race happening in a couple of location is: > > > > > > > > > > > > > > > > > > 1. disable IRQs (e.g. > > > > > > > > > arch_suspend_disable_irqs()) > > > > > > > > > ... > > > > > > > > > 2. syscore_suspend() > > > > > > > > > -> timekeeping_suspend() > > > > > > > > > -> clockevents_notify(SUSPEND) > > > > > > > > > -> tick_suspend() (timers are turned off here) > > > > > > > > > ... > > > > > > > > > 3. wfi (wait for wake-IRQ here) > > > > > > > > > > > > > > > > > > Between steps 1 and 2 the timers can still generate > > > > > > > > > interrupts that are > > > > > > > > > not handled and stay pending until step 3. That pending IRQ > > > > > > > > > causes an > > > > > > > > > immediate - spurious - wake. > > > > > > > > > > > > > > > > > > The solution is to move the clockevents suspend/resume > > > > > > > > > notification > > > > > > > > > out of the syscore_suspend step and explictly call them at > > > > > > > > > the appropriate > > > > > > > > > time in the suspend/hibernation paths. I.e. timers are > > > > > > > > > suspend _before_ > > > > > > > > > IRQs get disabled. And accordingly in the resume path. > > > > > > > > > > > > > > > > > > Signed-off-by: Soren Brinkmann <soren.brinkm...@xilinx.com> > > > > > > > > > --- > > > > > > > > > Hi, > > > > > > > > > > > > > > > > > > there was not a lot of discussion on the last submission. > > > > > > > > > Just one comment from > > > > > > > > > Rafael (https://lkml.org/lkml/2014/8/26/780), which - as I > > > > > > > > > outlined in my > > > > > > > > > response, does not apply, IMHO, since the platform does not > > > > > > > > > re-enable > > > > > > > > > interrupts. > > > > > > > > > > > > > > > > Well, you just don't agree with it. > > > > > > > > > > > > > > > > The problem with your approach is that timer interrupts aren't > > > > > > > > actually as > > > > > > > > special as you think and any other IRQF_NO_SUSPEND interrupts > > > > > > > > would have caused > > > > > > > > similar issues to appear under specific conditions. > > > > > > > > > > > > > > > > The solution I would suggest and that actually covers all > > > > > > > > IRQF_NO_SUSPEND > > > > > > > > interrupts would be to use a wait_event() loop like the one in > > > > > > > > freeze_enter() > > > > > > > > (on top of the current linux-next or the pm-genirq branch of > > > > > > > > linux-pm.git), > > > > > > > > but wait for pm_abort_suspend to become true, to implement > > > > > > > > system suspend. > > > > > > > > > > > > > > sorry, it took me a while since I needed to get some dependencies > > > > > > > ported > > > > > > > to the pm-genirq base. Once I had that, it reproduced my original > > > > > > > issue. > > > > > > > So far so good. I then looked into finding a solution following > > > > > > > your > > > > > > > guidance. I'm not sure I really found what you had in mind, but > > > > > > > below is > > > > > > > what I came up with, which seems to do it. > > > > > > > Please let me know how far off I am. > > > > > > > > > > > > > > Thanks, > > > > > > > Sören > > > > > > > > > > > > > > -------8<------------------8<----------------8<----------------8<--------------- > > > > > > > diff --git a/drivers/base/power/wakeup.c > > > > > > > b/drivers/base/power/wakeup.c > > > > > > > index c2744b30d5d9..a4f9914571f1 100644 > > > > > > > --- a/drivers/base/power/wakeup.c > > > > > > > +++ b/drivers/base/power/wakeup.c > > > > > > > @@ -25,7 +25,7 @@ > > > > > > > bool events_check_enabled __read_mostly; > > > > > > > > > > > > > > /* If set and the system is suspending, terminate the suspend. */ > > > > > > > -static bool pm_abort_suspend __read_mostly; > > > > > > > +bool pm_abort_suspend __read_mostly; > > > > > > > > > > > > > > /* > > > > > > > * Combined counters of registered wakeup events and wakeup > > > > > > > events in progress. > > > > > > > diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c > > > > > > > index 6dadb25cb0d8..e6a6de8f76d0 100644 > > > > > > > --- a/kernel/power/suspend.c > > > > > > > +++ b/kernel/power/suspend.c > > > > > > > @@ -33,6 +33,7 @@ > > > > > > > > > > > > > > static const char *pm_labels[] = { "mem", "standby", "freeze", }; > > > > > > > const char *pm_states[PM_SUSPEND_MAX]; > > > > > > > +extern bool pm_abort_suspend; > > > > > > > > > > > > > > static const struct platform_suspend_ops *suspend_ops; > > > > > > > static const struct platform_freeze_ops *freeze_ops; > > > > > > > @@ -294,25 +295,27 @@ static int suspend_enter(suspend_state_t > > > > > > > state, bool *wakeup) > > > > > > > if (error || suspend_test(TEST_CPUS)) > > > > > > > goto Enable_cpus; > > > > > > > > > > > > > > - arch_suspend_disable_irqs(); > > > > > > > - BUG_ON(!irqs_disabled()); > > > > > > > - > > > > > > > - error = syscore_suspend(); > > > > > > > - if (!error) { > > > > > > > - *wakeup = pm_wakeup_pending(); > > > > > > > - if (!(suspend_test(TEST_CORE) || *wakeup)) { > > > > > > > - trace_suspend_resume(TPS("machine_suspend"), > > > > > > > - state, true); > > > > > > > - error = suspend_ops->enter(state); > > > > > > > - trace_suspend_resume(TPS("machine_suspend"), > > > > > > > - state, false); > > > > > > > - events_check_enabled = false; > > > > > > > + while (!pm_abort_suspend) { > > > > > > > > > > > > That won't work in general, because pm_abort_suspend may not be set > > > > > > on some > > > > > > platforms on wakeup. It is only set if a wakeup interrupt triggers > > > > > > which > > > > > > may not be the case on ACPI systems if the BIOS has woken up the > > > > > > system. > > > > > > > > > > > > But that could be addressed by making those platforms simply set > > > > > > pm_wakeup_pending > > > > > > in their BIOS exit path. > > > > > > > > > > > > > + arch_suspend_disable_irqs(); > > > > > > > + BUG_ON(!irqs_disabled()); > > > > > > > + > > > > > > > + error = syscore_suspend(); > > > > > > > > > > > > Also it shouldn't be necessary to do > > > > > > syscore_suspend()/syscore_resume() in > > > > > > every iteration of the loop. > > > > > > > > > > > > > + if (!error) { > > > > > > > + *wakeup = pm_wakeup_pending(); > > > > > > > > > > > > Plus pm_wakeup_pending() returns true if pm_abort_suspend is set > > > > > > > > > > > > > + if (!(suspend_test(TEST_CORE) || *wakeup)) { > > > > > > > + > > > > > > > trace_suspend_resume(TPS("machine_suspend"), > > > > > > > + state, true); > > > > > > > > > > > > Did you try to add the loop here instead of above? Like: > > > > > > > > > > > > for (;;) { > > > > > > *wakeup = pm_wakeup_pending(); > > > > > > if (*wakeup) > > > > > > break; > > > > > > > > > > I think, that doesn't work. I chose the start/end points of the loop > > > > > to include the IRQ enable/disable calls. AFAICT, pm_abort_suspend is > > > > > set in an ISR. Without enabling interrupts the abort condition of > > > > > this loop never becomes true. > > > > > > > > Any further ideas how to resolve this? > > > > > > Sorry about the delay, lost track of this. > > > > > > You're right, the IRQ disabling/enabling needs to happen in the loop. > > > > > > So the direction of the patch looks OK, but it needs to ensure that > > > pm_wakeup_pending > > > is set properly by all platforms. Also it should be sufficient to check > > > pm_wakeup_pending() to detect wakeup. > > > > > > Have you tested the patch? > > > > Before considering this patch a solution, can I ask you to rewind > > the discussion a bit since I have a question. > > > > I thought that "suspending" the tick through syscore meant shutting down > > the respective clock_event_device, and that's how it is implemented in the > > kernel. > > > > Now, do we expect a shutdown clock_event_device to still signal pending > > IRQs ? I do not think that should be the case, at least that's not what > > happens for eg arm arch timers - ie disabling them implicitly gates > > the signal connected to the IRQ line. > > > > So the question is more related to the zynq platform and how their clock > > event device (which is ?) is shutdown, and what's the correct behaviour we > > are expecting. > > As outlined in the commit message, there is a race condition in the core > code. Looking at the timers is just fighting the symptoms.
I gathered there is a race condition between 1 and 2 in your code path. What I am asking you is why are we getting a pending IRQ at step 3 when the clock event device is supposed to be shutdown. My question is: Should a clock event device in shutdown mode (ie disabled) still signal IRQs to the interrupt controller (and consequently to the core) ? It is for me to understand if that's the behaviour we are expecting. > > FWIW, the problem here is not related to the simple wfi state on zynq, > > even some other ARM platforms with power management capabilities would wake > > up from the state entered by executing wfi (ie possibly through reset) if > > there is a pending timer IRQ, the question is more "should the IRQ be > > allowed to be there" instead IMHO. > > > > I still think that Stephen's query related to what timer is causing > > the wake-up is worth investigating. > > As I reported earlier, I see these spurious wakes with the cadence_ttc > as well as the ARM twd timers. I thought that a shutdown clock event device explicitly disables IRQ assertion, that's why I am inquiring, I do not understand how this can happen - how can you have a pending timer IRQ at step 3 above. Thanks, Lorenzo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
