linux-kernel - [patch] softlockup watchdog: fix Xen bogosity

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Message-ID: <20070717114453.GA8212@elte.hu>
Date:	Tue, 17 Jul 2007 13:44:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>, stable@...nel.org,
	Greg KH <greg@...ah.com>, Chris Wright <chrisw@...s-sol.org>
Subject: [patch] softlockup watchdog: fix Xen bogosity

Subject: softlockup: fix Xen bogosity
From: Ingo Molnar <mingo@...e.hu>

this Xen related commit:

   commit 966812dc98e6a7fcdf759cbfa0efab77500a8868
   Author: Jeremy Fitzhardinge <jeremy@...p.org>
   Date:   Tue May 8 00:28:02 2007 -0700

       Ignore stolen time in the softlockup watchdog

broke the softlockup watchdog to never report any lockups. (!)

print_timestamp defaults to 0, this makes the following condition
always true:

	if (print_timestamp < (touch_timestamp + 1) ||

and we'll never report soft lockups.

apparently the functionality of the soft lockup watchdog was never 
actually tested with that patch applied ...

[ this is -stable material too. ]

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/softlockup.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Index: linux/kernel/softlockup.c
===================================================================
--- linux.orig/kernel/softlockup.c
+++ linux/kernel/softlockup.c
@@ -79,10 +79,11 @@ void softlockup_tick(void)
 	print_timestamp = per_cpu(print_timestamp, this_cpu);
 
 	/* report at most once a second */
-	if (print_timestamp < (touch_timestamp + 1) ||
-		did_panic ||
-			!per_cpu(watchdog_task, this_cpu))
+	if ((print_timestamp >= touch_timestamp &&
+			print_timestamp < (touch_timestamp + 1)) ||
+			did_panic || !per_cpu(watchdog_task, this_cpu)) {
 		return;
+	}
 
 	/* do not print during early bootup: */
 	if (unlikely(system_state != SYSTEM_RUNNING)) {
-
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