On Tue, 24 Apr 2018 10:11:46 +0530 Shilpasri G Bhat <shilpa.b...@linux.vnet.ibm.com> wrote:
> gpstate_timer_handler() uses synchronous smp_call to set the pstate > on the requested core. This causes the below hard lockup: > > [c000003fe566b320] [c0000000001d5340] smp_call_function_single+0x110/0x180 > (unreliable) > [c000003fe566b390] [c0000000001d55e0] smp_call_function_any+0x180/0x250 > [c000003fe566b3f0] [c000000000acd3e8] gpstate_timer_handler+0x1e8/0x580 > [c000003fe566b4a0] [c0000000001b46b0] call_timer_fn+0x50/0x1c0 > [c000003fe566b520] [c0000000001b4958] expire_timers+0x138/0x1f0 > [c000003fe566b590] [c0000000001b4bf8] run_timer_softirq+0x1e8/0x270 > [c000003fe566b630] [c000000000d0d6c8] __do_softirq+0x158/0x3e4 > [c000003fe566b710] [c000000000114be8] irq_exit+0xe8/0x120 > [c000003fe566b730] [c000000000024d0c] timer_interrupt+0x9c/0xe0 > [c000003fe566b760] [c000000000009014] decrementer_common+0x114/0x120 > --- interrupt: 901 at doorbell_global_ipi+0x34/0x50 > LR = arch_send_call_function_ipi_mask+0x120/0x130 > [c000003fe566ba50] [c00000000004876c] > arch_send_call_function_ipi_mask+0x4c/0x130 (unreliable) > [c000003fe566ba90] [c0000000001d59f0] smp_call_function_many+0x340/0x450 > [c000003fe566bb00] [c000000000075f18] pmdp_invalidate+0x98/0xe0 > [c000003fe566bb30] [c0000000003a1120] change_huge_pmd+0xe0/0x270 > [c000003fe566bba0] [c000000000349278] change_protection_range+0xb88/0xe40 > [c000003fe566bcf0] [c0000000003496c0] mprotect_fixup+0x140/0x340 > [c000003fe566bdb0] [c000000000349a74] SyS_mprotect+0x1b4/0x350 > [c000003fe566be30] [c00000000000b184] system_call+0x58/0x6c > > Fix this by using the asynchronus smp_call in the timer interrupt handler. > We don't have to wait in this handler until the pstates are changed on > the core. This change will not have any impact on the global pstate > ramp-down algorithm. > > Reported-by: Nicholas Piggin <npig...@gmail.com> > Reported-by: Pridhiviraj Paidipeddi <ppaid...@linux.vnet.ibm.com> > Signed-off-by: Shilpasri G Bhat <shilpa.b...@linux.vnet.ibm.com> > --- > drivers/cpufreq/powernv-cpufreq.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/cpufreq/powernv-cpufreq.c > b/drivers/cpufreq/powernv-cpufreq.c > index 0591874..7e0c752 100644 > --- a/drivers/cpufreq/powernv-cpufreq.c > +++ b/drivers/cpufreq/powernv-cpufreq.c > @@ -721,7 +721,7 @@ void gpstate_timer_handler(struct timer_list *t) > spin_unlock(&gpstates->gpstate_lock); > > /* Timer may get migrated to a different cpu on cpu hot unplug */ > - smp_call_function_any(policy->cpus, set_pstate, &freq_data, 1); > + smp_call_function_any(policy->cpus, set_pstate, &freq_data, 0); > } > > /* This can still deadlock because !wait case still ends up having to wait if another !wait smp_call_function caller had previously used the call single data for this cpu. If you go this way you would have to use smp_call_function_async, which is more work. As a rule it would be better to avoid smp_call_function entirely if possible. Can you ensure the timer is running on the right CPU? Use add_timer_on and try again if the timer is on the wrong CPU, perhaps? Thanks, Nick
