Messages in this thread |  | | Date | Wed, 04 Dec 2013 22:24:25 +0100 | From | Daniel Lezcano <> | Subject | Re: [PATCH] cpuidle: Check for dev before deregistering it. |
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On 12/04/2013 05:09 PM, Konrad Rzeszutek Wilk wrote: > On Wed, Dec 04, 2013 at 10:10:28AM +0100, Daniel Lezcano wrote: >> On 12/03/2013 10:33 PM, Rafael J. Wysocki wrote: >>> On Tuesday, December 03, 2013 10:59:58 AM Konrad Rzeszutek Wilk wrote: >>>> If not, we could end up in the unfortunate situation where >>>> we dereference a NULL pointer b/c we have cpuidle disabled. >>>> >>>> This is the case when booting under Xen (which uses the >>>> ACPI P/C states but disables the CPU idle driver) - and can >>>> be easily reproduced when booting with cpuidle.off=1. >>>> >>>> BUG: unable to handle kernel NULL pointer dereference at (null) >>>> IP: [<ffffffff8156db4a>] cpuidle_unregister_device+0x2a/0x90 >>>> .. snip.. >>>> Call Trace: >>>> [<ffffffff813b15b4>] acpi_processor_power_exit+0x3c/0x5c >>>> [<ffffffff813af0a9>] acpi_processor_stop+0x61/0xb6 >>>> [<ffffffff814215bf>] __device_release_driver+0fffff81421653>] device_release_driver+0x23/0x30 >>>> [<ffffffff81420ed8>] bus_remove_device+0x108/0x180 >>>> [<ffffffff8141d9d9>] device_del+0x129/0x1c0 >>>> [<ffffffff813cb4b0>] ? unregister_xenbus_watch+0x1f0/0x1f0 >>>> [<ffffffff8141da8e>] device_unregister+0x1e/0x60 >>>> [<ffffffff814243e9>] unregister_cpu+0x39/0x60 >>>> [<ffffffff81019e03>] arch_unregister_cpu+0x23/0x30 >>>> [<ffffffff813c3c51>] handle_vcpu_hotplug_event+0xc1/0xe0 >>>> [<ffffffff813cb4f5>] xenwatch_thread+0x45/0x120 >>>> [<ffffffff810af010>] ? abort_exclusive_wait+0xb0/0xb0 >>>> [<ffffffff8108ec42>] kthread+0xd2/0xf0 >>>> [<ffffffff8108eb70>] ? kthread_create_on_node+0x180/0x180 >>>> [<ffffffff816ce17c>] ret_from_fork+0x7c/0xb0 >>>> [<ffffffff8108eb70>] ? kthread_create_on_node+0x180/0x180 >>>> >>>> This problem also appears in 3.12 and could be a candidate for backport. >>>> >>>> CC: "Rafael J. Wysocki" <rjw@rjwysocki.net> >>>> CC: Daniel Lezcano <daniel.lezcano@linaro.org> >>>> CC: linux-pm@vger.kernel.org >>>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> >>> >>> Applied, thanks! >>> >>>> --- >>>> drivers/cpuidle/cpuidle.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c >>>> index 2a991e4..a55e68f 100644 >>>> --- a/drivers/cpuidle/cpuidle.c >>>> +++ b/drivers/cpuidle/cpuidle.c >>>> @@ -400,7 +400,7 @@ EXPORT_SYMBOL_GPL(cpuidle_register_device); >>>> */ >>>> void cpuidle_unregister_device(struct cpuidle_device *dev) >>>> { >>>> - if (dev->registered == 0) >>>> + if (!dev || dev->registered == 0) >>>> return; >>>> >>>> cpuidle_pause_and_lock(); >> >> Oops, wait. Are we sure the problem is coming from cpuidle ? > > It is acpi_processor_power_exit assuming that the cpuidle is > initialized. It could be fixed there too, but there are multiple > entries in cpuidle where it does the : "if (!dev) return .." > so I figured this should be done as well here.
I understand.
From my POV the bug is coming from the acpi processor idle driver.
The function acpi_processor_power_init registers the cpuidle driver and the cpuidle device when acpi_processor_registered is zero. Then it increments acpi_processor_registered preventing the next call to this function to register the driver but it will register the device.
As cpuidle is disabled, the cpuidle_register_driver fails, thus the device is not registered and acpi_processor_registered is not incremented. So all calls to acpi_processor_power_init prevents the driver and the device to be registered. No problem with that.
But the function acpi_processor_power_exit does not take care of the value of acpi_processor_registered and just unregister the device. Then it decrements acpi_processor_registered which is zero to -1.
Trying to be immune from a NULL pointer in cpuidle_unregister_device hides bogus code from the caller. So IMO, this check shouldn't be there and the acpi_processor_power_exit function should be fixed instead.
>> The cpuidle_unregister_device is called with a NULL pointer, that >> shouldn't happen. > > It does :-) >> >> Konrad, you say that could be easily reproduced. How do you produce >> it ? Unplugging a cpu ? > > Yes. >
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