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    SubjectRe: [PATCH tip/core/rcu 02/15] rcu: Pull TINY_RCU dyntick-idle tracing into non-idle region
    On Thu, Aug 30, 2012 at 11:56:15AM -0700, Paul E. McKenney wrote:
    > From: "Paul E. McKenney" <paul.mckenney@linaro.org>
    >
    > Because TINY_RCU's idle detection keys directly off of the nesting
    > level, rather than from a separate variable as in TREE_RCU, the
    > TINY_RCU dyntick-idle tracing on transition to idle must happen
    > before the change to the nesting level. This commit therefore makes
    > this change by passing the desired new value (rather than the old value)
    > of the nesting level in to rcu_idle_enter_common().
    >
    > [ paulmck: Add fix for wrong-variable bug spotted by
    > Michael Wang <wangyun@linux.vnet.ibm.com>. ]
    >
    > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
    > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    Reviewed-by: Josh Triplett <josh@joshtriplett.org>

    > ---
    > kernel/rcutiny.c | 31 ++++++++++++++++---------------
    > 1 files changed, 16 insertions(+), 15 deletions(-)
    >
    > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
    > index 547b1fe..e4163c5 100644
    > --- a/kernel/rcutiny.c
    > +++ b/kernel/rcutiny.c
    > @@ -56,24 +56,27 @@ static void __call_rcu(struct rcu_head *head,
    > static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
    >
    > /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
    > -static void rcu_idle_enter_common(long long oldval)
    > +static void rcu_idle_enter_common(long long newval)
    > {
    > - if (rcu_dynticks_nesting) {
    > + if (newval) {
    > RCU_TRACE(trace_rcu_dyntick("--=",
    > - oldval, rcu_dynticks_nesting));
    > + rcu_dynticks_nesting, newval));
    > + rcu_dynticks_nesting = newval;
    > return;
    > }
    > - RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
    > + RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
    > if (!is_idle_task(current)) {
    > struct task_struct *idle = idle_task(smp_processor_id());
    >
    > RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
    > - oldval, rcu_dynticks_nesting));
    > + rcu_dynticks_nesting, newval));
    > ftrace_dump(DUMP_ALL);
    > WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
    > current->pid, current->comm,
    > idle->pid, idle->comm); /* must be idle task! */
    > }
    > + barrier();
    > + rcu_dynticks_nesting = newval;
    > rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
    > }
    >
    > @@ -84,17 +87,16 @@ static void rcu_idle_enter_common(long long oldval)
    > void rcu_idle_enter(void)
    > {
    > unsigned long flags;
    > - long long oldval;
    > + long long newval;
    >
    > local_irq_save(flags);
    > - oldval = rcu_dynticks_nesting;
    > WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
    > if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
    > DYNTICK_TASK_NEST_VALUE)
    > - rcu_dynticks_nesting = 0;
    > + newval = 0;
    > else
    > - rcu_dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
    > - rcu_idle_enter_common(oldval);
    > + newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
    > + rcu_idle_enter_common(newval);
    > local_irq_restore(flags);
    > }
    > EXPORT_SYMBOL_GPL(rcu_idle_enter);
    > @@ -105,13 +107,12 @@ EXPORT_SYMBOL_GPL(rcu_idle_enter);
    > void rcu_irq_exit(void)
    > {
    > unsigned long flags;
    > - long long oldval;
    > + long long newval;
    >
    > local_irq_save(flags);
    > - oldval = rcu_dynticks_nesting;
    > - rcu_dynticks_nesting--;
    > - WARN_ON_ONCE(rcu_dynticks_nesting < 0);
    > - rcu_idle_enter_common(oldval);
    > + newval = rcu_dynticks_nesting - 1;
    > + WARN_ON_ONCE(newval < 0);
    > + rcu_idle_enter_common(newval);
    > local_irq_restore(flags);
    > }
    >
    > --
    > 1.7.8
    >


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