Fix discrepancy between VDSO based gettimeofday() and sys_gettimeofday().

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>
Acked-by: 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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 8a67e282cb5e..f24e8acdec91 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -64,6 +64,16 @@ struct vsyscall_gtod_data __vsyscall_gtod_data __section_vsyscall_gtod_data =
         .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;
@@ -77,7 +87,6 @@ void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
         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_to_monotonic = wall_to_monotonic;
         write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
 }