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

Anton Vorontsov
2012-03-07T13:54:06Z

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

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>
---

This is respin of http://lkml.org/lkml/2012/1/3/265, which does not
apply cleanly nowadays.

drivers/staging/android/lowmemorykiller.c | 14 +++++++-------
1 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index cf4c6f7..03d1de2 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -75,10 +75,10 @@ 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;
}

@@ -175,14 +175,12 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
selected->pid, selected->comm,
selected_oom_score_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
send_sig(SIGKILL, selected, 0);
rem -= selected_tasksize;
@@ -200,6 +198,7 @@ static struct shrinker lowmem_shrinker = {

static int __init lowmem_init(void)
{
+ task_handoff_register(&task_nb);
register_shrinker(&lowmem_shrinker);
return 0;
}
@@ -207,6 +206,7 @@ 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);
--
1.7.7.6