Commit 8aeee85a authored by Anton Blanchard's avatar Anton Blanchard Committed by Linus Torvalds
Browse files

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: default avatarAnton Blanchard <anton@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 78d7d407

kernel/panic.c

+30 −16
Original line number Diff line number Diff line
@@ -36,15 +36,36 @@ ATOMIC_NOTIFIER_HEAD(panic_notifier_list); 


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 @@ NORET_TYPE void panic(const char * fmt, ...) 


	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 @@ NORET_TYPE void panic(const char * fmt, ...) 
		 */

		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 @@ NORET_TYPE void panic(const char * fmt, ...) 
	}

#endif

	local_irq_enable();

	for (i = 0; ; ) {

	while (1) {

		touch_softlockup_watchdog();

		i += panic_blink(i);

		mdelay(1);

		i++;

		panic_blink_one_second();

	}

}

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