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>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e48311e8c923aaaec93f4f14791c088c1c995508..30473ee9628b710b874f03be9d2eb745297b7088 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1724,6 +1724,9 @@ extern cputime_t task_utime(struct task_struct *p);
 extern cputime_t task_stime(struct task_struct *p);
 extern cputime_t task_gtime(struct task_struct *p);
 
+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 166b8c49257c589750f0b67479011ba7bac97038..2cfa6dcfd44f0c015007b4c69761e83b0f1ff286 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -138,6 +138,9 @@ 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));
@@ -156,6 +159,18 @@ void free_task(struct task_struct *tsk)
 }
 EXPORT_SYMBOL(free_task);
 
+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);
@@ -165,6 +180,7 @@ void __put_task_struct(struct task_struct *tsk)
        exit_creds(tsk);
        delayacct_tsk_free(tsk);
 
+       atomic_notifier_call_chain(&task_free_notifier, 0, tsk);
        if (!profile_handoff_task(tsk))
                free_task(tsk);
 }