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

diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c
index 05cccbc..83332fe 100644 (file)
--- 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;
 }