From: Tony Breeds <tony@bakeyournoodle.com>

On platforms that copy sys_tz into the vdso (currently only x86_64, soon to
include powerpc), it is possible for the vdso to get out of sync if a user
calls (admittedly unusual) settimeofday(NULL, ptr).

This patch adds a hook for architectures that set
CONFIG_GENERIC_TIME_VSYSCALL to ensure when sys_tz is updated they can also
updatee their copy in the vdso.

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/ia64/kernel/time.c       |    5 +++++
 arch/x86_64/kernel/vsyscall.c |   11 ++++++++++-
 include/linux/clocksource.h   |    5 +++++
 kernel/time.c                 |    2 ++
 4 files changed, 22 insertions(+), 1 deletion(-)

diff -puN arch/ia64/kernel/time.c~fix-discrepancy-between-vdso-based-gettimeofday-and-sys_gettimeofday arch/ia64/kernel/time.c
--- a/arch/ia64/kernel/time.c~fix-discrepancy-between-vdso-based-gettimeofday-and-sys_gettimeofday
+++ a/arch/ia64/kernel/time.c
@@ -371,6 +371,11 @@ ia64_setup_printk_clock(void)
 		ia64_printk_clock = ia64_itc_printk_clock;
 }
 
+/* IA64 doesn't cache the timezone */
+void update_vsyscall_tz(void)
+{
+}
+
 void update_vsyscall(struct timespec *wall, struct clocksource *c)
 {
         unsigned long flags;
diff -puN arch/x86_64/kernel/vsyscall.c~fix-discrepancy-between-vdso-based-gettimeofday-and-sys_gettimeofday arch/x86_64/kernel/vsyscall.c
--- a/arch/x86_64/kernel/vsyscall.c~fix-discrepancy-between-vdso-based-gettimeofday-and-sys_gettimeofday
+++ a/arch/x86_64/kernel/vsyscall.c
@@ -66,6 +66,16 @@ struct vsyscall_gtod_data __vsyscall_gto
 	.sysctl_enabled = 1,
 };
 
+void update_vsyscall_tz(void)
+{
+	unsigned long flags;
+
+	write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
+	/* sys_tz has changed */
+	vsyscall_gtod_data.sys_tz = sys_tz;
+	write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
+}
+
 void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
 {
 	unsigned long flags;
@@ -79,7 +89,6 @@ void update_vsyscall(struct timespec *wa
 	vsyscall_gtod_data.clock.shift = clock->shift;
 	vsyscall_gtod_data.wall_time_sec = wall_time->tv_sec;
 	vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
-	vsyscall_gtod_data.sys_tz = sys_tz;
 	vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
 	vsyscall_gtod_data.wall_to_monotonic = wall_to_monotonic;
 	write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
diff -puN include/linux/clocksource.h~fix-discrepancy-between-vdso-based-gettimeofday-and-sys_gettimeofday include/linux/clocksource.h
--- a/include/linux/clocksource.h~fix-discrepancy-between-vdso-based-gettimeofday-and-sys_gettimeofday
+++ a/include/linux/clocksource.h
@@ -222,10 +222,15 @@ extern void clocksource_touch_watchdog(v
 
 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
+extern void update_vsyscall_tz(void);
 #else
 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 {
 }
+
+static inline void update_vsyscall_tz(void)
+{
+}
 #endif
 
 #endif /* _LINUX_CLOCKSOURCE_H */
diff -puN kernel/time.c~fix-discrepancy-between-vdso-based-gettimeofday-and-sys_gettimeofday kernel/time.c
--- a/kernel/time.c~fix-discrepancy-between-vdso-based-gettimeofday-and-sys_gettimeofday
+++ a/kernel/time.c
@@ -30,6 +30,7 @@
 #include <linux/module.h>
 #include <linux/timex.h>
 #include <linux/capability.h>
+#include <linux/clocksource.h>
 #include <linux/errno.h>
 #include <linux/syscalls.h>
 #include <linux/security.h>
@@ -162,6 +163,7 @@ int do_sys_settimeofday(struct timespec 
 	if (tz) {
 		/* SMP safe, global irq locking makes it work. */
 		sys_tz = *tz;
+		update_vsyscall_tz();
 		if (firsttime) {
 			firsttime = 0;
 			if (!tv)
_