Android sched: Add a generic notifier when a task struct is about to be freed

This patch adds a notifier which can be used by subsystems that may
be interested in when a task has completely died and is about to
have it's last resource freed.
The Android lowmemory killer uses this to determine when a task
it has killed has finally given up its goods.

Signed-off-by: San Mehat <san@google.com>

3 files changed, 40 insertions, 0 deletions

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index 4235bc69e6c2..c242bb348f1a 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -63,6 +63,24 @@ static struct task_struct *lowmem_deathpending;
 			printk(x);			\
 	} while (0)
 
+static int
+task_notify_func(struct notifier_block *self, unsigned long val, void *data);
+
+static struct notifier_block task_nb = {
+	.notifier_call	= task_notify_func,
+};
+
+static int
+task_notify_func(struct notifier_block *self, unsigned long val, void *data)
+{
+	struct task_struct *task = data;
+	if (task == lowmem_deathpending) {
+		lowmem_deathpending = NULL;
+		task_free_unregister(&task_nb);
+	}
+	return NOTIFY_OK;
+}
+
 static int lowmem_shrink(struct shrinker *s, int nr_to_scan, gfp_t gfp_mask)
 {
 	struct task_struct *p;
@@ -162,6 +180,7 @@ static int lowmem_shrink(struct shrinker *s, int nr_to_scan, gfp_t gfp_mask)
 			     selected->pid, selected->comm,
 			     selected_oom_adj, selected_tasksize);
 		lowmem_deathpending = selected;
+		task_free_register(&task_nb);
 		force_sig(SIGKILL, selected);
 		rem -= selected_tasksize;
 	}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5ee397ee3bca..794b8f447d03 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1682,6 +1682,9 @@ static inline void put_task_struct(struct task_struct *t)
 extern void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st);
 extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st);
 
+extern int task_free_register(struct notifier_block *n);
+extern int task_free_unregister(struct notifier_block *n);
+
 /*
  * Per process flags
  */
diff --git a/kernel/fork.c b/kernel/fork.c
index b6cce14ba047..19615bcae7fe 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -147,6 +147,9 @@ struct kmem_cache *vm_area_cachep;
 /* SLAB cache for mm_struct structures (tsk->mm) */
 static struct kmem_cache *mm_cachep;
 
+/* Notifier list called when a task struct is freed */
+static ATOMIC_NOTIFIER_HEAD(task_free_notifier);
+
 static void account_kernel_stack(struct thread_info *ti, int account)
 {
 	struct zone *zone = page_zone(virt_to_page(ti));
@@ -177,6 +180,20 @@ static inline void put_signal_struct(struct signal_struct *sig)
 		free_signal_struct(sig);
 }
 
+int task_free_register(struct notifier_block *n)
+{
+	return atomic_notifier_chain_register(&task_free_notifier, n);
+}
+
+EXPORT_SYMBOL(task_free_register);
+
+int task_free_unregister(struct notifier_block *n)
+{
+	return atomic_notifier_chain_unregister(&task_free_notifier, n);
+}
+
+EXPORT_SYMBOL(task_free_unregister);
+
 void __put_task_struct(struct task_struct *tsk)
 {
 	WARN_ON(!tsk->exit_state);
@@ -187,6 +204,7 @@ void __put_task_struct(struct task_struct *tsk)
 	delayacct_tsk_free(tsk);
 	put_signal_struct(tsk->signal);
 
+	atomic_notifier_call_chain(&task_free_notifier, 0, tsk);
 	if (!profile_handoff_task(tsk))
 		free_task(tsk);
 }