[v4] timers/migration: Fix three possible races and some improvements

[PATCH v4 7/8] timers/migration: Spare write when nothing changed

Posted by Anna-Maria Behnsen 1 year, 5 months ago

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.

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.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 5c206e71c212..d9f7e9b77f11 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1215,14 +1215,13 @@ 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

[tip: timers/urgent] timers/migration: Spare write when nothing changed

Posted by tip-bot2 for Anna-Maria Behnsen 1 year, 4 months ago

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

Commit-ID:     2367e28e231af05243b92325de9a38956ad0b565
Gitweb:        https://git.kernel.org/tip/2367e28e231af05243b92325de9a38956ad0b565
Author:        Anna-Maria Behnsen <anna-maria@linutronix.de>
AuthorDate:    Tue, 16 Jul 2024 16:19:25 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 22 Jul 2024 18:03:34 +02:00

timers/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 the write to the place where wakeup value is changed changed.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20240716-tmigr-fixes-v4-7-757baa7803fe@linutronix.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 ca76120..9c15ae8 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1215,14 +1215,13 @@ 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;

[tip: timers/urgent] timers/migration: Spare write when nothing changed

Posted by tip-bot2 for Anna-Maria Behnsen 1 year, 5 months ago

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

Commit-ID:     7aa42d6722d3b2fe4b78e40148feaa5194b46f16
Gitweb:        https://git.kernel.org/tip/7aa42d6722d3b2fe4b78e40148feaa5194b46f16
Author:        Anna-Maria Behnsen <anna-maria@linutronix.de>
AuthorDate:    Tue, 16 Jul 2024 16:19:25 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 19 Jul 2024 19:58:02 +02:00

timers/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 the write to the place where wakeup value is changed changed.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20240716-tmigr-fixes-v4-7-757baa7803fe@linutronix.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 66c3437..9b80e8a 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1215,14 +1215,13 @@ 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;