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    SubjectRe: [PATCH 2/8] rcu: remove irq/softirq context check in rcu_read_unlock_special()
    On Wed, Aug 07, 2013 at 06:24:58PM +0800, Lai Jiangshan wrote:
    > After patch 10f39bb1, "special & RCU_READ_UNLOCK_BLOCKED" can't be true
    > in irq nor softirq.(due to RCU_READ_UNLOCK_BLOCKED can only be set
    > when preemption)
    >
    > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    > ---
    > kernel/rcutree_plugin.h | 6 ------
    > 1 files changed, 0 insertions(+), 6 deletions(-)
    >
    > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    > index 8fd947e..54f7e45 100644
    > --- a/kernel/rcutree_plugin.h
    > +++ b/kernel/rcutree_plugin.h
    > @@ -361,12 +361,6 @@ void rcu_read_unlock_special(struct task_struct *t)
    > rcu_preempt_qs(smp_processor_id());
    > }
    >
    > - /* Hardware IRQ handlers cannot block. */
    > - if (in_irq() || in_serving_softirq()) {
    > - local_irq_restore(flags);
    > - return;
    > - }
    > -

    Good point, it is time to relax the redundant checking. Paranoid that
    I am, I took an intermediate position, wrapping a WARN_ON_ONCE() around
    the check as follows:

    if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
    local_irq_restore(flags);
    return;
    }

    If this warning never triggers over a period of some time, we can remove
    it entirely.

    I have queued this for 3.14 with your Signed-off-by. Please let me know
    if you have any objections.

    Thanx, Paul

    > /* Clean up if blocked during RCU read-side critical section. */
    > if (special & RCU_READ_UNLOCK_BLOCKED) {
    > t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
    > --
    > 1.7.4.4
    >



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