On Tue, Jun 23, 2020 at 8:30 AM Chen Yu <[email protected]> wrote: > > Suspend to idle was found to not work on Goldmont CPU recently. > And the issue was triggered due to: > > 1. On Goldmont the CPU in idle can only be woken up via IPIs, > not POLLING mode: > Commit 08e237fa56a1 ("x86/cpu: Add workaround for MONITOR > instruction erratum on Goldmont based CPUs") > 2. When the CPU is entering suspend to idle process, the > _TIF_POLLING_NRFLAG is kept on, due to cpuidle_enter_s2idle() > doesn't properly match call_cpuidle(). > 3. Commit b2a02fc43a1f ("smp: Optimize send_call_function_single_ipi()") > makes use of _TIF_POLLING_NRFLAG to avoid sending IPIs to > idle CPUs. > 4. As a result, some IPIs related functions might not work > well during suspend to idle on Goldmont. For example, one > suspected victim: > tick_unfreeze() -> timekeeping_resume() -> hrtimers_resume() > -> clock_was_set() -> on_each_cpu() might wait forever, > because the IPIs will not be sent to the CPUs which are > sleeping with _TIF_POLLING_NRFLAG set, and Goldmont CPU > could not be woken up by only setting _TIF_NEED_RESCHED > on the monitor address. > > Clear the _TIF_POLLING_NRFLAG flag before entering suspend to idle, > and let the driver's enter_s2idle() to decide whether to set > _TIF_POLLING_NRFLAG or not. So that to avoid the scenario described > above and keep the context consistent with before. > > Fixes: b2a02fc43a1f ("smp: Optimize send_call_function_single_ipi()") > Reported-by: kbuild test robot <[email protected]> > Cc: "Rafael J. Wysocki" <[email protected]> > Cc: Peter Zijlstra (Intel) <[email protected]> > Cc: Len Brown <[email protected]> > Signed-off-by: Chen Yu <[email protected]>
Applied (based on the previous discussion) with some subject and changelog edits. Thanks! > --- > v2: According to Peter's review, v1 is racy, if someone already > set TIF_NEED_RESCHED this patch just clear POLLING and go to sleep. > Check TIF_NEED_RESCHED before entering suspend to idle and > adjust the naming to be consistent with call_cpuidle(). > > v3: According to Rafael, it would be better to do the simplest fix > first and then do the cleanup on top of it. > --- > drivers/cpuidle/cpuidle.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c > index c149d9e20dfd..e092789187c6 100644 > --- a/drivers/cpuidle/cpuidle.c > +++ b/drivers/cpuidle/cpuidle.c > @@ -13,6 +13,7 @@ > #include <linux/mutex.h> > #include <linux/sched.h> > #include <linux/sched/clock.h> > +#include <linux/sched/idle.h> > #include <linux/notifier.h> > #include <linux/pm_qos.h> > #include <linux/cpu.h> > @@ -186,7 +187,7 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, > struct cpuidle_device *dev) > * be frozen safely. > */ > index = find_deepest_state(drv, dev, U64_MAX, 0, true); > - if (index > 0) > + if (index > 0 && !current_clr_polling_and_test()) > enter_s2idle_proper(drv, dev, index); > > return index; > -- > 2.17.1 >
