Add irq protection in the percpu-counters cpu-hotplug-callback path

Some of the per-cpu counters and thus their locks are accessed from IRQ
contexts.  This can cause a deadlock if it interrupts a cpu-offline thread
which is transferring a dead-cpu's counts to the global counter.

Add appropriate IRQ protection in the cpu-hotplug callback path.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 9659eabffc31..393a0e915c23 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -124,12 +124,13 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
         mutex_lock(&percpu_counters_lock);
         list_for_each_entry(fbc, &percpu_counters, list) {
                 s32 *pcount;
+                unsigned long flags;
 
-                spin_lock(&fbc->lock);
+                spin_lock_irqsave(&fbc->lock, flags);
                 pcount = per_cpu_ptr(fbc->counters, cpu);
                 fbc->count += *pcount;
                 *pcount = 0;
-                spin_unlock(&fbc->lock);
+                spin_unlock_irqrestore(&fbc->lock, flags);
         }
         mutex_unlock(&percpu_counters_lock);
         return NOTIFY_OK;