linux-kernel - [PATCH 1/5] time: Move clock_was_set_seq update to before we update the shadow-timekeeper

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Date:	Thu, 11 Jun 2015 15:54:53 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	linux-kernel@...r.kernel.org
Cc:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 1/5] time: Move clock_was_set_seq update to before we update the shadow-timekeeper

It was reported that 868a3e915f7f5eba (hrtimer: Make offset
update smarter) was causing timer problems after suspend/resume.

The problem with that change is the modification to
clock_was_set_seq in timekeeping_update is done prior to
mirroring the time state to the shadow-timekeeper. Thus the
next time we do update_wall_time() the updated sequence is
overwritten by whats in the shadow copy.

This patch moves the shadow-timekeeper mirroring to the end
of the function, after all updates have been made, so all data
is kept in sync.

(This patch also affects the update_fast_timekeeper calls which
were also problematically done prior to the mirroring).

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Reported-by: Jeremiah Mahler <jmmahler@...il.com>
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 kernel/time/timekeeping.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 90ed5db..849b932 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -585,15 +585,19 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action)
 	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));
-
 	update_fast_timekeeper(&tk->tkr_mono, &tk_fast_mono);
 	update_fast_timekeeper(&tk->tkr_raw,  &tk_fast_raw);
 
 	if (action & TK_CLOCK_WAS_SET)
 		tk->clock_was_set_seq++;
+	/*
+	 * The mirroring of the data to the shadow-timekeeper needs
+	 * to happen last here to ensure we don't over-write the
+	 * timekeeper structure on the next update with stale data
+	 */
+	if (action & TK_MIRROR)
+		memcpy(&shadow_timekeeper, &tk_core.timekeeper,
+		       sizeof(tk_core.timekeeper));
 }
 
 /**
-- 
1.9.1

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