panic: fix panic_timeout accuracy when running on a hypervisor
I've had some complaints about panic_timeout being wildly innacurate on
shared processor PowerPC partitions (a 3 minute panic_timeout taking 30
minutes).
The problem is we loop on mdelay(1) and with a 1ms in 10ms hypervisor
timeslice each of these will take 10ms (ie 10x) longer. I expect other
platforms with shared processor hypervisors will see the same issue.
This patch keeps the old behaviour if we have a panic_blink (only keyboard
LEDs right now) and does 1 second mdelays if we don't.
Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/panic.c b/kernel/panic.c
index c787333..13d966b 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -36,15 +36,36 @@
EXPORT_SYMBOL(panic_notifier_list);
-static long no_blink(long time)
-{
- return 0;
-}
-
/* Returns how long it waited in ms */
long (*panic_blink)(long time);
EXPORT_SYMBOL(panic_blink);
+static void panic_blink_one_second(void)
+{
+ static long i = 0, end;
+
+ if (panic_blink) {
+ end = i + MSEC_PER_SEC;
+
+ while (i < end) {
+ i += panic_blink(i);
+ mdelay(1);
+ i++;
+ }
+ } else {
+ /*
+ * When running under a hypervisor a small mdelay may get
+ * rounded up to the hypervisor timeslice. For example, with
+ * a 1ms in 10ms hypervisor timeslice we might inflate a
+ * mdelay(1) loop by 10x.
+ *
+ * If we have nothing to blink, spin on 1 second calls to
+ * mdelay to avoid this.
+ */
+ mdelay(MSEC_PER_SEC);
+ }
+}
+
/**
* panic - halt the system
* @fmt: The text string to print
@@ -95,9 +116,6 @@
bust_spinlocks(0);
- if (!panic_blink)
- panic_blink = no_blink;
-
if (panic_timeout > 0) {
/*
* Delay timeout seconds before rebooting the machine.
@@ -105,11 +123,9 @@
*/
printk(KERN_EMERG "Rebooting in %d seconds..", panic_timeout);
- for (i = 0; i < panic_timeout*1000; ) {
+ for (i = 0; i < panic_timeout; i++) {
touch_nmi_watchdog();
- i += panic_blink(i);
- mdelay(1);
- i++;
+ panic_blink_one_second();
}
/*
* This will not be a clean reboot, with everything
@@ -135,11 +151,9 @@
}
#endif
local_irq_enable();
- for (i = 0; ; ) {
+ while (1) {
touch_softlockup_watchdog();
- i += panic_blink(i);
- mdelay(1);
- i++;
+ panic_blink_one_second();
}
}