percpu_counter: fix CPU unplug race in percpu_counter_destroy()

We should first delete the counter from percpu_counters list
before freeing memory, or a percpu_counter_hotcpu_callback()
could dereference a NULL pointer.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a8663890a88c..71b265c330ce 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -104,13 +104,13 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
         if (!fbc->counters)
                 return;
 
-        free_percpu(fbc->counters);
-        fbc->counters = NULL;
 #ifdef CONFIG_HOTPLUG_CPU
         mutex_lock(&percpu_counters_lock);
         list_del(&fbc->list);
         mutex_unlock(&percpu_counters_lock);
 #endif
+        free_percpu(fbc->counters);
+        fbc->counters = NULL;
 }
 EXPORT_SYMBOL(percpu_counter_destroy);