timekeeping: Update timekeeper before updating vsyscall and pvclock

The update_walltime() code works on the shadow timekeeper to make the
seqcount protected region as short as possible. But that update to the
shadow timekeeper does not update all timekeeper fields because it's
sufficient to do that once before it becomes life. One of these fields
is tkr.base_mono. That stays stale in the shadow timekeeper unless an
operation happens which copies the real timekeeper to the shadow.

The update function is called after the update calls to vsyscall and
pvclock. While not correct, it did not cause any problems because none
of the invoked update functions used base_mono.

commit cbcf2dd3b3d4 (x86: kvm: Make kvm_get_time_and_clockread()
nanoseconds based) changed that in the kvm pvclock update function, so
the stale mono_base value got used and caused kvm-clock to malfunction.

Put the update where it belongs and fix the issue.

Reported-by: Chris J Arges <chris.j.arges@canonical.com>
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1409050000570.3333@nanos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index fb4a9c2cf8d98db2256a6268fb8bbfb37673b2fe..ec1791fae96575ffe49c9aa1a2f42cbc6b21df2a 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -442,11 +442,12 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action)
                tk->ntp_error = 0;
                ntp_clear();
        }
-       update_vsyscall(tk);
-       update_pvclock_gtod(tk, action & TK_CLOCK_WAS_SET);
 
        tk_update_ktime_data(tk);
 
+       update_vsyscall(tk);
+       update_pvclock_gtod(tk, action & TK_CLOCK_WAS_SET);
+
        if (action & TK_MIRROR)
                memcpy(&shadow_timekeeper, &tk_core.timekeeper,
                       sizeof(tk_core.timekeeper));