softirq: make migrate disable/enable conditioned on softirq_nestcnt transition

This patch removes the recursive calls to migrate_disable/enable in
local_bh_disable/enable

the softirq-local-lock.patch introduces local_bh_disable/enable wich
decrements/increments the current->softirq_nestcnt and disable/enables
migration as well. as softirq_nestcnt (include/linux/sched.h conditioned
on CONFIG_PREEMPT_RT_BASE) already is tracking the nesting level of the
recursive calls to local_bh_disable/enable (all in kernel/softirq.c) - no
need to do it twice.

migrate_disable/enable thus can be conditionsed on softirq_nestcnt making
a transition from 0-1 to disable migration and 1-0 to re-enable it.

No change of functional behavior, this does noticably reduce the observed
nesting level of migrate_disable/enable

Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 916ffed7bba3129e3d006e937df78f1caf877863..588bae073f1ee35e9e103c2f8d4bc4ffb166f705 100644 (file)
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -557,8 +557,8 @@ static void do_current_softirqs(int need_rcu_bh_qs)
 
 static void __local_bh_disable(void)
 {
-       migrate_disable();
-       current->softirq_nestcnt++;
+       if (++current->softirq_nestcnt == 1)
+               migrate_disable();
 }
 
 void local_bh_disable(void)
@@ -584,8 +584,8 @@ static void __local_bh_enable(void)
                do_current_softirqs(1);
        local_irq_enable();
 
-       current->softirq_nestcnt--;
-       migrate_enable();
+       if (--current->softirq_nestcnt == 0)
+               migrate_enable();
 }
 
 void local_bh_enable(void)
@@ -609,8 +609,10 @@ EXPORT_SYMBOL(local_bh_enable_ip);
 
 void _local_bh_enable(void)
 {
-       current->softirq_nestcnt--;
-       migrate_enable();
+       if (WARN_ON(current->softirq_nestcnt == 0))
+               return;
+       if (--current->softirq_nestcnt == 0)
+               migrate_enable();
 }
 EXPORT_SYMBOL(_local_bh_enable);