linux-kernel - [tip: locking/core] time/sched_clock: Swap update_clock_read

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Message-ID: <173089006394.32228.1285388463688281244.tip-bot2@tip-bot2>
Date: Wed, 06 Nov 2024 10:47:43 -0000
From: "tip-bot2 for Marco Elver" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Marco Elver <elver@...gle.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: locking/core] time/sched_clock: Swap update_clock_read_data()
 latch writes

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

Commit-ID:     1139c71df5ca29a36f08e3a08c7cee160db21ec1
Gitweb:        https://git.kernel.org/tip/1139c71df5ca29a36f08e3a08c7cee160db21ec1
Author:        Marco Elver <elver@...gle.com>
AuthorDate:    Mon, 04 Nov 2024 16:43:05 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 05 Nov 2024 12:55:34 +01:00

time/sched_clock: Swap update_clock_read_data() latch writes

Swap the writes to the odd and even copies to make the writer critical
section look like all other seqcount_latch writers.

Signed-off-by: Marco Elver <elver@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20241104161910.780003-2-elver@google.com
---
 kernel/time/sched_clock.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index 68d6c11..85595fc 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -119,9 +119,6 @@ unsigned long long notrace sched_clock(void)
  */
 static void update_clock_read_data(struct clock_read_data *rd)
 {
-	/* update the backup (odd) copy with the new data */
-	cd.read_data[1] = *rd;
-
 	/* steer readers towards the odd copy */
 	raw_write_seqcount_latch(&cd.seq);
 
@@ -130,6 +127,9 @@ static void update_clock_read_data(struct clock_read_data *rd)
 
 	/* switch readers back to the even copy */
 	raw_write_seqcount_latch(&cd.seq);
+
+	/* update the backup (odd) copy with the new data */
+	cd.read_data[1] = *rd;
 }
 
 /*