leds: heartbeat: fix bug on panic

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> Signed-off-by: Bryan Wu <bryan.wu@canonical.com>

leds: heartbeat: fix bug on panic
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> Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
Alexander Holler · Bryan Wu
1 parent 9e85a6f9dc
Showing 1 changed file with 15 additions and 1 deletions Side-by-side Diff
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 @@
 	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 @@
 	return NOTIFY_DONE;
 }
  
+static int heartbeat_panic_notifier(struct notifier_block *nb,
+				     unsigned long code, void *unused)
+{
+	panic_heartbeats = 1;
+	return NOTIFY_DONE;
+}
+
 static struct notifier_block heartbeat_reboot_nb = {
 	.notifier_call = heartbeat_reboot_notifier,
 };
  
 static struct notifier_block heartbeat_panic_nb = {
-	.notifier_call = heartbeat_reboot_notifier,
+	.notifier_call = heartbeat_panic_notifier,
 };
  
 static int __init heartbeat_trig_init(void)
...	...	@@ -21,6 +21,8 @@
21	21	#include <linux/reboot.h>
22	22	#include "leds.h"
23	23
	24	+static int panic_heartbeats;
	25	+
24	26	struct heartbeat_trig_data {
25	27	unsigned int phase;
26	28	unsigned int period;
...	...	@@ -34,6 +36,11 @@
34	36	unsigned long brightness = LED_OFF;
35	37	unsigned long delay = 0;
36	38
	39	+ if (unlikely(panic_heartbeats)) {
	40	+ led_set_brightness(led_cdev, LED_OFF);
	41	+ return;
	42	+ }
	43	+
37	44	/* acts like an actual heart beat -- ie thump-thump-pause... */
38	45	switch (heartbeat_data->phase) {
39	46	case 0:
40	47
...	...	@@ -111,12 +118,19 @@
111	118	return NOTIFY_DONE;
112	119	}
113	120
	121	+static int heartbeat_panic_notifier(struct notifier_block *nb,
	122	+ unsigned long code, void *unused)
	123	+{
	124	+ panic_heartbeats = 1;
	125	+ return NOTIFY_DONE;
	126	+}
	127	+
114	128	static struct notifier_block heartbeat_reboot_nb = {
115	129	.notifier_call = heartbeat_reboot_notifier,
116	130	};
117	131
118	132	static struct notifier_block heartbeat_panic_nb = {
119		- .notifier_call = heartbeat_reboot_notifier,
	133	+ .notifier_call = heartbeat_panic_notifier,
120	134	};
121	135
122	136	static int __init heartbeat_trig_init(void)