[patch 32/49] uml: deal with host time going backwards

[Greg KH]

2.6.25-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Jeff Dike <jdike@xxxxxxxxxxx>

commit 06e1e4ffbd1932e288839b3140cda6b8141eb684 upstream

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@xxxxxxxxxxxxx>
Signed-off-by: Jeff Dike <jdike@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 arch/um/os-Linux/time.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- 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 t
 		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 });

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