Messages in this thread | | | Date | Wed, 04 Jul 2012 09:11:03 +0200 | From | Alexander Holler <> | Subject | Re: [PATCH] leds: heartbeat: fix bug on panic |
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Am 04.07.2012 09:05, schrieb Bryan Wu: > On Tue, Jul 3, 2012 at 2:35 PM, Alexander Holler <holler@ahsoftware.de> 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@ahsoftware.de> >> --- >> 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.
Regards,
Alexander
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