On 18 December 2014 at 11:58, Ethan Zhao <ethan.z...@oracle.com> wrote: > If _PPC changed notification happens before governor was initiated while > kernel > is booting, a NULL pointer dereference will be triggered: > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000030 > IP: [<ffffffff81470453>] __cpufreq_governor+0x23/0x1e0 > PGD 0 > Oops: 0000 [#1] SMP > ... ... > RIP: 0010:[<ffffffff81470453>] [<ffffffff81470453>] > __cpufreq_governor+0x23/0x1e0 > RSP: 0018:ffff881fcfbcfbb8 EFLAGS: 00010286 > RAX: 0000000000000000 RBX: ffff881fd11b3980 RCX: ffff88407fc20000 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff881fd11b3980 > RBP: ffff881fcfbcfbd8 R08: 0000000000000000 R09: 000000000000000f > R10: ffffffff818068d0 R11: 0000000000000043 R12: 0000000000000004 > R13: 0000000000000000 R14: ffffffff8196cae0 R15: 0000000000000000 > FS: 0000000000000000(0000) GS:ffff881fffc00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000030 CR3: 00000000018ae000 CR4: 00000000000407f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Process kworker/0:3 (pid: 750, threadinfo ffff881fcfbce000, task > ffff881fcf556400) > Stack: > ffff881fffc17d00 ffff881fcfbcfc18 ffff881fd11b3980 0000000000000000 > ffff881fcfbcfc08 ffffffff81470d08 ffff881fd11b3980 0000000000000007 > ffff881fcfbcfc18 ffff881fffc17d00 ffff881fcfbcfd28 ffffffff81472e9a > Call Trace: > [<ffffffff81470d08>] __cpufreq_set_policy+0x1b8/0x2e0 > [<ffffffff81472e9a>] cpufreq_update_policy+0xca/0x150 > [<ffffffff81472f20>] ? cpufreq_update_policy+0x150/0x150 > [<ffffffff81324a96>] acpi_processor_ppc_has_changed+0x71/0x7b > [<ffffffff81320bcd>] acpi_processor_notify+0x55/0x115 > [<ffffffff812f9c29>] acpi_device_notify+0x19/0x1b > [<ffffffff813084ca>] acpi_ev_notify_dispatch+0x41/0x5f > [<ffffffff812f64a4>] acpi_os_execute_deferred+0x27/0x34 > > The root cause is a race conditon -- cpufreq core and acpi-cpufreq driver > were initiated, but cpufreq_governor wasn't and _PPC changed notification > happened, __cpufreq_governor() was called within acpi_os_execute_deferred > kernel thread context. > > To fix this panic issue, add pointer checking code in __cpufreq_governor() > before pointer policy->governor is to be dereferenced. > > Signed-off-by: Ethan Zhao <ethan.z...@oracle.com> > Acked-by: Viresh Kumar <viresh.ku...@linaro.org> > --- > v2&v3: correct comment style. > > drivers/cpufreq/cpufreq.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 4473eba..b75735c 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -2021,6 +2021,11 @@ static int __cpufreq_governor(struct cpufreq_policy > *policy, > /* Don't start any governor operations if we are entering suspend */ > if (cpufreq_suspended) > return 0; > + /* > + * Governor might not be initiated here if _PPC changed notification > + * happened, check it. > + */ > + if (!policy->governor) > + return -EINVAL; > > if (policy->governor->max_transition_latency && > policy->cpuinfo.transition_latency >
It will take me sometime to get cpufreq core simplified, till that time Acked-by: Viresh Kumar <viresh.ku...@linaro.org> to yet another band-aid :) -- 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/
