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>

diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a8663890a88c2e358f21b8cdc6f23a8ebb9d77e5..71b265c330ce364326328151a03fec07c3e9adb0 100644 (file)
--- 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);