linux-kernel - [PATCH] fix jiffy calculations in calibrate_delay

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Message-Id: <4D53B4F10200007800031323@vpn.id2.novell.com>
Date:	Thu, 10 Feb 2011 08:50:41 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	<akpm@...ux-foundation.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Tim Deegan" <Tim.Deegan@...rix.com>,
	"Jeremy Fitzhardinge" <jeremy@...p.org>, <stable@...nel.org>,
	"Jiri Slaby" <jslaby@...e.cz>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] fix jiffy calculations in calibrate_delay_direct to
	 handle overflow

From: Tim Deegan <Tim.Deegan@...rix.com>

Fixes a hang when booting as dom0 under Xen, when jiffies can be
quite large by the time the kernel init gets this far.

Signed-off-by: Tim Deegan <Tim.Deegan@...rix.com>
[jbeulich@...ell.com: !time_after() -> time_before_eq() as suggested by Jiri Slaby]
Signed-off-by: Jan Beulich <jbeulich@...ell.com>
Cc: Jiri Slaby <jslaby@...e.cz>
Cc: Jeremy Fitzhardinge <jeremy@...p.org>
Cc: stable@...nel.org 

---
 init/calibrate.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- 2.6.38-rc4/init/calibrate.c
+++ 2.6.38-rc4-calibrate-jiffy-overflow/init/calibrate.c
@@ -66,7 +66,7 @@ static unsigned long __cpuinit calibrate
 		pre_start = 0;
 		read_current_timer(&start);
 		start_jiffies = jiffies;
-		while (jiffies <= (start_jiffies + 1)) {
+		while (time_before_eq(jiffies, start_jiffies + 1)) {
 			pre_start = start;
 			read_current_timer(&start);
 		}
@@ -74,8 +74,8 @@ static unsigned long __cpuinit calibrate
 
 		pre_end = 0;
 		end = post_start;
-		while (jiffies <=
-		       (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {
+		while (time_before_eq(jiffies, start_jiffies + 1 +
+					       DELAY_CALIBRATION_TICKS)) {
 			pre_end = end;
 			read_current_timer(&end);
 		}



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