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rcu: Per-CPU operation cleanups to rcu_*_qs() functions

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The rcu_bh_qs(), rcu_preempt_qs(), and rcu_sched_qs() functions use
old-style per-CPU variable access and write to ->passed_quiesce even
if it is already set.  This commit therefore updates to use the new-style
per-CPU variable access functions and avoids the spurious writes.
This commit also eliminates the "cpu" argument to these functions because
they are always invoked on the indicated CPU.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
2014-08-14 16:38:46 -07:00
parent 1d082fd061
commit 284a8c93af
6 changed files with 41 additions and 36 deletions
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25
kernel/rcu/tree_plugin.h
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@@ -158,14 +158,16 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed);
* As with the other rcu_*_qs() functions, callers to this function
* must disable preemption.
*/
static void rcu_preempt_qs(int cpu)
static void rcu_preempt_qs(void)
{
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
if (rdp->passed_quiesce == 0)
trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
rdp->passed_quiesce = 1;
current->rcu_read_unlock_special.b.need_qs = false;
if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) {
trace_rcu_grace_period(TPS("rcu_preempt"),
__this_cpu_read(rcu_preempt_data.gpnum),
TPS("cpuqs"));
__this_cpu_write(rcu_preempt_data.passed_quiesce, 1);
barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
current->rcu_read_unlock_special.b.need_qs = false;
}
}
/*
@@ -256,7 +258,7 @@ static void rcu_preempt_note_context_switch(int cpu)
* grace period, then the fact that the task has been enqueued
* means that we continue to block the current grace period.
*/
rcu_preempt_qs(cpu);
rcu_preempt_qs();
}
/*
@@ -352,7 +354,7 @@ void rcu_read_unlock_special(struct task_struct *t)
*/
special = t->rcu_read_unlock_special;
if (special.b.need_qs) {
rcu_preempt_qs(smp_processor_id());
rcu_preempt_qs();
if (!t->rcu_read_unlock_special.s) {
local_irq_restore(flags);
return;
@@ -651,11 +653,12 @@ static void rcu_preempt_check_callbacks(int cpu)
struct task_struct *t = current;
if (t->rcu_read_lock_nesting == 0) {
rcu_preempt_qs(cpu);
rcu_preempt_qs();
return;
}
if (t->rcu_read_lock_nesting > 0 &&
per_cpu(rcu_preempt_data, cpu).qs_pending)
per_cpu(rcu_preempt_data, cpu).qs_pending &&
!per_cpu(rcu_preempt_data, cpu).passed_quiesce)
t->rcu_read_unlock_special.b.need_qs = true;
}