linux-kernel - [PATCH 6/14] uml: deal with host time going backwards

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Date:	Fri, 1 Aug 2008 18:41:28 -0400
From:	Jeff Dike <jdike@...toit.com>
To:	stable@...nel.org
Cc:	LKML <linux-kernel@...r.kernel.org>,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	Nix <nix@...eri.org.uk>
Subject: [PATCH 6/14] uml: deal with host time going backwards

>From b547462b600e9d284f9d40ed558ca2b8904af185 Mon Sep 17 00:00:00 2001

Protection against the host's time going backwards (eg, ntp activity on
the host) by keeping track of the time at the last tick and if it's
greater than the current time, keep time stopped until the host catches
up.

Cc: Nix <nix@...eri.org.uk>
Signed-off-by: Jeff Dike <jdike@...ux.intel.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
---
 arch/um/os-Linux/time.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index bee98f4..dec5678 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -106,6 +106,10 @@ static void deliver_alarm(void)
 	unsigned long long this_tick = os_nsecs();
 	int one_tick = UM_NSEC_PER_SEC / UM_HZ;
 
+	/* Protection against the host's time going backwards */
+	if ((last_tick != 0) && (this_tick < last_tick))
+		this_tick = last_tick;
+
 	if (last_tick == 0)
 		last_tick = this_tick - one_tick;
 
@@ -148,6 +152,9 @@ static int after_sleep_interval(struct timespec *ts)
 		start_usecs = usec;
 
 	start_usecs -= skew / UM_NSEC_PER_USEC;
+	if (start_usecs < 0)
+		start_usecs = 0;
+
 	tv = ((struct timeval) { .tv_sec  = start_usecs / UM_USEC_PER_SEC,
 				 .tv_usec = start_usecs % UM_USEC_PER_SEC });
 	interval = ((struct itimerval) { { 0, usec }, tv });
-- 
1.5.5.1
--
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