Re: [PATCH] leds: heartbeat: fix bug on panic

[Bryan Wu]

On Wed, Jul 4, 2012 at 3:11 PM, Alexander Holler <holler@xxxxxxxxxxxxx> wrote:
> Am 04.07.2012 09:05, schrieb Bryan Wu:
>
>> On Tue, Jul 3, 2012 at 2:35 PM, Alexander Holler <holler@xxxxxxxxxxxxx>
>> wrote:
>>>
>>> With commit 49dca5aebfdeadd4bf27b6cb4c60392147dc35a4 I introduced
>>> a bug (visible if CONFIG_PROVE_RCU is enabled) which occures when a panic
>>> has happened:
>>>
>>> [ 1526.520230] ===============================
>>> [ 1526.520230] [ INFO: suspicious RCU usage. ]
>>> [ 1526.520230] 3.5.0-rc1+ #12 Not tainted
>>> [ 1526.520230] -------------------------------
>>> [ 1526.520230] /c/kernel-tests/mm/include/linux/rcupdate.h:436 Illegal
>>> context switch in RCU read-side critical section!
>>> [ 1526.520230]
>>> [ 1526.520230] other info that might help us debug this:
>>> [ 1526.520230]
>>> [ 1526.520230]
>>> [ 1526.520230] rcu_scheduler_active = 1, debug_locks = 0
>>> [ 1526.520230] 3 locks held by net.agent/3279:
>>> [ 1526.520230]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff82f85962>]
>>> do_page_fault+0x193/0x390
>>> [ 1526.520230]  #1:  (panic_lock){+.+...}, at: [<ffffffff82ed2830>]
>>> panic+0x37/0x1d3
>>> [ 1526.520230]  #2:  (rcu_read_lock){.+.+..}, at: [<ffffffff810b9b28>]
>>> rcu_lock_acquire+0x0/0x29
>>> [ 1526.520230]
>>> [ 1526.520230] stack backtrace:
>>> [ 1526.520230] Pid: 3279, comm: net.agent Not tainted 3.5.0-rc1+ #12
>>> [ 1526.520230] Call Trace:
>>> [ 1526.520230]  [<ffffffff810e1570>] lockdep_rcu_suspicious+0x109/0x112
>>> [ 1526.520230]  [<ffffffff810bfe3a>] rcu_preempt_sleep_check+0x45/0x47
>>> [ 1526.520230]  [<ffffffff810bfe5a>] __might_sleep+0x1e/0x19a
>>> [ 1526.520230]  [<ffffffff82f8010e>] down_write+0x26/0x81
>>> [ 1526.520230]  [<ffffffff8276a966>] led_trigger_unregister+0x1f/0x9c
>>> [ 1526.520230]  [<ffffffff8276def5>] heartbeat_reboot_notifier+0x15/0x19
>>> [ 1526.520230]  [<ffffffff82f85bf5>] notifier_call_chain+0x96/0xcd
>>> [ 1526.520230]  [<ffffffff82f85cba>]
>>> __atomic_notifier_call_chain+0x8e/0xff
>>> [ 1526.520230]  [<ffffffff81094b7c>] ? kmsg_dump+0x37/0x1eb
>>> [ 1526.520230]  [<ffffffff82f85d3f>] atomic_notifier_call_chain+0x14/0x16
>>> [ 1526.520230]  [<ffffffff82ed28e1>] panic+0xe8/0x1d3
>>> [ 1526.520230]  [<ffffffff811473e2>] out_of_memory+0x15d/0x1d3
>>>
>>> So in case of a panic, now just turn of the LED. Other approaches like
>>> scheduling a work to unregister the trigger aren't working because there
>>> isn't much which still runs after a panic occured (except timers).
>>>
>>> Signed-off-by: Alexander Holler <holler@xxxxxxxxxxxxx>
>>> ---
>>>   drivers/leds/ledtrig-heartbeat.c |   16 +++++++++++++++-
>>>   1 files changed, 15 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/drivers/leds/ledtrig-heartbeat.c
>>> b/drivers/leds/ledtrig-heartbeat.c
>>> index 41dc76d..a019fbb 100644
>>> --- a/drivers/leds/ledtrig-heartbeat.c
>>> +++ b/drivers/leds/ledtrig-heartbeat.c
>>> @@ -21,6 +21,8 @@
>>>   #include <linux/reboot.h>
>>>   #include "leds.h"
>>>
>>> +static int panic_heartbeats;
>>> +
>>>   struct heartbeat_trig_data {
>>>          unsigned int phase;
>>>          unsigned int period;
>>> @@ -34,6 +36,11 @@ static void led_heartbeat_function(unsigned long data)
>>>          unsigned long brightness = LED_OFF;
>>>          unsigned long delay = 0;
>>>
>>> +       if (unlikely(panic_heartbeats)) {
>>> +               led_set_brightness(led_cdev, LED_OFF);
>>> +               return;
>>> +       }
>>> +
>>>          /* acts like an actual heart beat -- ie thump-thump-pause... */
>>>          switch (heartbeat_data->phase) {
>>>          case 0:
>>> @@ -111,12 +118,19 @@ static int heartbeat_reboot_notifier(struct
>>> notifier_block *nb,
>>>          return NOTIFY_DONE;
>>>   }
>>>
>>> +static int heartbeat_panic_notifier(struct notifier_block *nb,
>>> +                                    unsigned long code, void *unused)
>>> +{
>>> +       panic_heartbeats = 1;
>>
>>
>> Can we just set LED as OFF and delete the timer here? because timer is
>> also useless after a kernel panic.
>> So we don't need this global static variable here.
>
>
> No, the necessary information (heartbeat_trig_data) isn't available here.
>

Yeah, looks like there is no way to pass heartbeat_trig_data
information to the notifier call function.
Anyway, I will apply this patch to my for-next branch.

Thanks,
-- 
Bryan Wu <bryan.wu@xxxxxxxxxxxxx>
Kernel Developer    +86.186-168-78255 Mobile
Canonical Ltd.      www.canonical.com
Ubuntu - Linux for human beings | www.ubuntu.com
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