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