[PATCH v2 7/8] flex_proportions: Disable preemption entering the write section.

[Sebastian Andrzej Siewior]

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

diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c
index 05cccbcf1661a..83332fefa6f42 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;
 }
-- 
2.37.2