linux-kernel - [PATCH 2/3] timer_migration: Spare write when nothing changed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20240621-tmigr-fixes-v1-2-8c8a2d8e8d77@linutronix.de>
Date: Fri, 21 Jun 2024 11:37:07 +0200
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH 2/3] timer_migration: Spare write when nothing changed

The wakeup value is written unconditionally in tmigr_cpu_new_timer(). When
there was no new next timer expiry that needs to be propagated, then the
value that was read before is written. This is not required.

Move write to the place where wakeup value could have changed.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
 kernel/time/timer_migration.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index d91efe1dc3bf..f55be5411ad9 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1237,14 +1237,13 @@ u64 tmigr_cpu_new_timer(u64 nextexp)
 		if (nextexp != tmc->cpuevt.nextevt.expires ||
 		    tmc->cpuevt.ignore) {
 			ret = tmigr_new_timer(tmc, nextexp);
+			/*
+			 * Make sure the reevaluation of timers in idle path
+			 * will not miss an event.
+			 */
+			WRITE_ONCE(tmc->wakeup, ret);
 		}
 	}
-	/*
-	 * Make sure the reevaluation of timers in idle path will not miss an
-	 * event.
-	 */
-	WRITE_ONCE(tmc->wakeup, ret);
-
 	trace_tmigr_cpu_new_timer_idle(tmc, nextexp);
 	raw_spin_unlock(&tmc->lock);
 	return ret;

-- 
2.39.2