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    Subject[PATCH RT 03/11] timer/rt: Always raise the softirq if theres irq_work to be done
    3.10.32-rt31-rc1 stable review patch.
    If anyone has any objections, please let me know.


    From: Steven Rostedt <>

    It was previously discovered that some systems would hang on boot up
    with a previous version of 3.12-rt. This was due to RCU using irq_work,
    and RT defers the irq_work to a softirq. But if there's no active
    timers, the softirq will not be raised, and RCU work will not get done,
    causing the system to hang. The fix was to check that if there was no
    active timers but irq_work to be done, then we should raise the softirq.

    But this fix was not 100% correct. It left out the case that there were
    active timers that were not expired yet. This would have the softirq
    not get raised even if there was irq work to be done.

    If there is irq_work to be done, then we must raise the timer softirq
    regardless of if there is active timers or whether they are expired or
    not. The softirq can handle those cases. But we can never ignore

    As it is only PREEMPT_RT_FULL that requires irq_work to be done in the
    softirq, we can pull out the check in the active_timers condition, and
    make the code a bit cleaner by having the irq_work check separate, and
    put the code in with the other #ifdef PREEMPT_RT. If there is irq_work
    to be done, there's no need to check the active timers or if they are
    expired. Just raise the time softirq and be done with it. Otherwise, we
    can do the timer checks just like we do with non -rt.

    Signed-off-by: Steven Rostedt <>
    Signed-off-by: Sebastian Andrzej Siewior <>
    kernel/timer.c | 16 +++++++++-------
    1 file changed, 9 insertions(+), 7 deletions(-)

    diff --git a/kernel/timer.c b/kernel/timer.c
    index 25a38c4..f63a793 100644
    --- a/kernel/timer.c
    +++ b/kernel/timer.c
    @@ -1461,18 +1461,20 @@ void run_local_timers(void)
    * the timer softirq.
    + /* On RT, irq work runs from softirq */
    + if (irq_work_needs_cpu()) {
    + raise_softirq(TIMER_SOFTIRQ);
    + return;
    + }
    if (!spin_do_trylock(&base->lock)) {
    - if (!base->active_timers) {
    - /* On RT, irq work runs from softirq */
    - if (!irq_work_needs_cpu())
    - goto out;
    - }
    + if (!base->active_timers)
    + goto out;

    /* Check whether the next pending timer has expired */
    if (time_before_eq(base->next_timer, jiffies))

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      Last update: 2014-02-28 15:21    [W:15.237 / U:0.004 seconds]
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