staging: android/lowmemorykiller: Don't unregister notifier from atomic context

commit 1eda5166c7640092f512138be6899d050c3d62ed upstream.

The lowmemorykiller registers an atomic notifier for notfication of when
the task is freed.  From this atomic notifier callback, it removes the
atomic notifier via task_free_unregister().  This is incorrect because
atomic_notifier_chain_unregister() calls syncronize_rcu(), which can
sleep, which shouldn't be done from an atomic notifier.

Fix this by registering the notifier during init, and only unregister it
if the lowmemorykiller is unloaded.

Rebased to -next by Paul E. McKenney.
Rebased to -next again by Anton Vorontsov.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Christian Bejram <christian.bejram@stericsson.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reported-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 7 deletions

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index efc7dc1f483..5cd23096cc6 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -73,10 +73,10 @@ static int
 task_notify_func(struct notifier_block *self, unsigned long val, void *data)
 {
 	struct task_struct *task = data;
-	if (task == lowmem_deathpending) {
+
+	if (task == lowmem_deathpending)
 		lowmem_deathpending = NULL;
-		task_handoff_unregister(&task_nb);
-	}
+
 	return NOTIFY_OK;
 }
 
@@ -174,14 +174,12 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
 			     selected->pid, selected->comm,
 			     selected_oom_adj, selected_tasksize);
 		/*
-		 * If CONFIG_PROFILING is off, then task_handoff_register()
-		 * is a nop. In that case we don't want to stall the killer
-		 * by setting lowmem_deathpending.
+		 * If CONFIG_PROFILING is off, then we don't want to stall
+		 * the killer by setting lowmem_deathpending.
 		 */
 #ifdef CONFIG_PROFILING
 		lowmem_deathpending = selected;
 		lowmem_deathpending_timeout = jiffies + HZ;
-		task_handoff_register(&task_nb);
 #endif
 		force_sig(SIGKILL, selected);
 		rem -= selected_tasksize;
@@ -199,6 +197,7 @@ static struct shrinker lowmem_shrinker = {
 
 static int __init lowmem_init(void)
 {
+	task_handoff_register(&task_nb);
 	register_shrinker(&lowmem_shrinker);
 	return 0;
 }
@@ -206,6 +205,7 @@ static int __init lowmem_init(void)
 static void __exit lowmem_exit(void)
 {
 	unregister_shrinker(&lowmem_shrinker);
+	task_handoff_unregister(&task_nb);
 }
 
 module_param_named(cost, lowmem_shrinker.seeks, int, S_IRUGO | S_IWUSR);