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    SubjectRe: [PATCH tip/core/rcu 13/15] rcu: Move TINY_PREEMPT_RCU away from raw_local_irq_save()
    On Thu, Aug 30, 2012 at 11:56:26AM -0700, Paul E. McKenney wrote:
    > From: "Paul E. McKenney" <paul.mckenney@linaro.org>
    >
    > The use of raw_local_irq_save() is unnecessary, given that local_irq_save()
    > really does disable interrupts. Also, it appears to interfere with lockdep.
    > Therefore, this commit moves to local_irq_save().

    It looks like the non-raw versions also include tracing, which typically
    has recursive dependency problems with RCU. Can all of these call sites
    safely call into tracing without recursing back into RCU?

    - Josh Triplett

    > Reported-by: Fengguang Wu <fengguang.wu@intel.com>
    > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
    > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > Tested-by: Fengguang Wu <fengguang.wu@intel.com>
    > ---
    > kernel/rcutiny_plugin.h | 10 +++++-----
    > 1 files changed, 5 insertions(+), 5 deletions(-)
    >
    > diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
    > index 918fd1e..3d01902 100644
    > --- a/kernel/rcutiny_plugin.h
    > +++ b/kernel/rcutiny_plugin.h
    > @@ -278,7 +278,7 @@ static int rcu_boost(void)
    > rcu_preempt_ctrlblk.exp_tasks == NULL)
    > return 0; /* Nothing to boost. */
    >
    > - raw_local_irq_save(flags);
    > + local_irq_save(flags);
    >
    > /*
    > * Recheck with irqs disabled: all tasks in need of boosting
    > @@ -287,7 +287,7 @@ static int rcu_boost(void)
    > */
    > if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
    > rcu_preempt_ctrlblk.exp_tasks == NULL) {
    > - raw_local_irq_restore(flags);
    > + local_irq_restore(flags);
    > return 0;
    > }
    >
    > @@ -317,7 +317,7 @@ static int rcu_boost(void)
    > t = container_of(tb, struct task_struct, rcu_node_entry);
    > rt_mutex_init_proxy_locked(&mtx, t);
    > t->rcu_boost_mutex = &mtx;
    > - raw_local_irq_restore(flags);
    > + local_irq_restore(flags);
    > rt_mutex_lock(&mtx);
    > rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
    >
    > @@ -991,9 +991,9 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
    > {
    > unsigned long flags;
    >
    > - raw_local_irq_save(flags);
    > + local_irq_save(flags);
    > rcp->qlen -= n;
    > - raw_local_irq_restore(flags);
    > + local_irq_restore(flags);
    > }
    >
    > /*
    > --
    > 1.7.8
    >


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