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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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