[tip: sched/rt] flex_proportions: Disable preemption entering the write section.

["tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@linutronix.de>]

The following commit has been merged into the sched/rt branch of tip:

Commit-ID:     9458e0a78c45bc6537ce11eb9f03489eab92f9c2
Gitweb:        https://git.kernel.org/tip/9458e0a78c45bc6537ce11eb9f03489eab92f9c2
Author:        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate:    Thu, 25 Aug 2022 18:41:30 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 19 Sep 2022 14:35:08 +02:00

flex_proportions: Disable preemption entering the write section.

The seqcount fprop_global::sequence is not associated with a lock. The
write section (fprop_new_period()) is invoked from a timer and since the
softirq is preemptible on PREEMPT_RT it is possible to preempt the write
section which is not desited.

Disable preemption around the write section on PREEMPT_RT.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220825164131.402717-8-bigeasy@linutronix.de

---
 lib/flex_proportions.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c
index 05cccbc..83332fe 100644
--- a/lib/flex_proportions.c
+++ b/lib/flex_proportions.c
@@ -70,6 +70,7 @@ bool fprop_new_period(struct fprop_global *p, int periods)
 	 */
 	if (events <= 1)
 		return false;
+	preempt_disable_nested();
 	write_seqcount_begin(&p->sequence);
 	if (periods < 64)
 		events -= events >> periods;
@@ -77,6 +78,7 @@ bool fprop_new_period(struct fprop_global *p, int periods)
 	percpu_counter_add(&p->events, -events);
 	p->period += periods;
 	write_seqcount_end(&p->sequence);
+	preempt_enable_nested();
 
 	return true;
 }