linux-kernel - [tip: timers/core] timekeeping: Provide timekeeping_restore

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Message-ID: <172987928047.1442.163274573376384169.tip-bot2@tip-bot2>
Date: Fri, 25 Oct 2024 18:01:20 -0000
From: "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
 "Anna-Maria Behnsen" <anna-maria@...utronix.de>,
 John Stultz <jstultz@...gle.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timekeeping: Provide timekeeping_restore_shadow()

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     97e53792538dd8993172e231f09dadee57f66d69
Gitweb:        https://git.kernel.org/tip/97e53792538dd8993172e231f09dadee57f66d69
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Wed, 09 Oct 2024 10:29:08 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 25 Oct 2024 19:49:14 +02:00

timekeeping: Provide timekeeping_restore_shadow()

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>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: John Stultz <jstultz@...gle.com>
Link: https://lore.kernel.org/all/20241009-devel-anna-maria-b4-timers-ptp-timekeeping-v2-15-554456a44a15@linutronix.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 c30b187..ed0e328 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -774,6 +774,15 @@ 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);
@@ -801,7 +810,7 @@ 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_from_shadow(struct tk_data *tkd, unsigned int action)