linux-kernel - [PATCH 14/24] timekeeping: Provide timekeeping_restore

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Message-Id: <20240911-devel-anna-maria-b4-timers-ptp-timekeeping-v1-14-f7cae09e25d6@linutronix.de>
Date: Wed, 11 Sep 2024 15:29:58 +0200
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: John Stultz <jstultz@...gle.com>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
 Miroslav Lichvar <mlichvar@...hat.com>, 
 Richard Cochran <richardcochran@...il.com>, 
 Christopher S Hall <christopher.s.hall@...el.com>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH 14/24] timekeeping: Provide timekeeping_restore_shadow()

From: Thomas Gleixner <tglx@...utronix.de>

Functions which operate on the real timekeeper, e.g. do_settimeofday(),
have error conditions. If they are hit a full timekeeping update is still
required because the already committed operations modified the timekeeper.

When switching these functions to operate on the shadow timekeeper then the
full update can be avoided in the error case, but the modified shadow
timekeeper has to be restored.

Provide a helper function for that.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
 kernel/time/timekeeping.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index a69850429fb4..345117ff665d 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -755,6 +755,15 @@ static inline void tk_update_ktime_data(struct timekeeper *tk)
 	tk->tkr_raw.base = ns_to_ktime(tk->raw_sec * NSEC_PER_SEC);
 }
 
+/*
+ * Restore the shadow timekeeper from the real timekeeper.
+ */
+static void timekeeping_restore_shadow(struct tk_data *tkd)
+{
+	lockdep_assert_held(&tkd->lock);
+	memcpy(&tkd->shadow_timekeeper, &tkd->timekeeper, sizeof(tkd->timekeeper));
+}
+
 static void timekeeping_update(struct tk_data *tkd, struct timekeeper *tk, unsigned int action)
 {
 	lockdep_assert_held(&tkd->lock);
@@ -782,7 +791,7 @@ static void timekeeping_update(struct tk_data *tkd, struct timekeeper *tk, unsig
 	 * timekeeper structure on the next update with stale data
 	 */
 	if (action & TK_MIRROR)
-		memcpy(&tkd->shadow_timekeeper, tk, sizeof(*tk));
+		timekeeping_restore_shadow(tkd);
 }
 
 static void timekeeping_update_staged(struct tk_data *tkd, unsigned int action)

-- 
2.39.2