On Thu, Aug 30, 2012 at 11:56:15AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mcken...@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 <wang...@linux.vnet.ibm.com>. ]
>
> Signed-off-by: Paul E. McKenney <paul.mcken...@linaro.org>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <j...@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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