ANDROID: signal: Add vendor hook for memory reaping

Add vendor hook to determine if the memory of a process that received
the SIGKILL can be reaped.

Bug: 189803002
Change-Id: Ie6802b9bf93ddffb0ceef615d7cca40c23219e57
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>

drivers/android/vendor_hooks.c

@@ -83,6 +83,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_binder_set_priority);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_binder_restore_priority);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_binder_wakeup_ilocked);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_do_send_sig_info);
+EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_process_killed);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_rwsem_init);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_rwsem_wake);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_rwsem_write_finished);

include/linux/oom.h

@@ -129,4 +129,7 @@ extern struct task_struct *find_lock_task_mm(struct task_struct *p);
 extern int sysctl_oom_dump_tasks;
 extern int sysctl_oom_kill_allocating_task;
 extern int sysctl_panic_on_oom;
+
+/* call for adding killed process to reaper. */
+extern void add_to_oom_reaper(struct task_struct *p);
 #endif /* _INCLUDE_LINUX_OOM_H */

include/trace/hooks/signal.h

@@ -12,6 +12,9 @@ struct task_struct;
 DECLARE_HOOK(android_vh_do_send_sig_info,
 	TP_PROTO(int sig, struct task_struct *killer, struct task_struct *dst),
 	TP_ARGS(sig, killer, dst));
+DECLARE_HOOK(android_vh_process_killed,
+	TP_PROTO(struct task_struct *task, bool *reap),
+	TP_ARGS(task, reap));
 #endif /* _TRACE_HOOK_SIGNAL_H */
 /* This part must be outside protection */
 #include <trace/define_trace.h>

kernel/signal.c

@@ -46,6 +46,7 @@
 #include <linux/livepatch.h>
 #include <linux/cgroup.h>
 #include <linux/audit.h>
+#include <linux/oom.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/signal.h>
@@ -1413,8 +1414,16 @@ int group_send_sig_info(int sig, struct kernel_siginfo *info,
 	ret = check_kill_permission(sig, info, p);
 	rcu_read_unlock();
 
-	if (!ret && sig)
+	if (!ret && sig) {
 		ret = do_send_sig_info(sig, info, p, type);
+		if (!ret && sig == SIGKILL) {
+			bool reap = false;
+
+			trace_android_vh_process_killed(current, &reap);
+			if (reap)
+				add_to_oom_reaper(p);
+		}
+	}
 
 	return ret;
 }

mm/oom_kill.c

@@ -724,6 +724,20 @@ static inline void wake_oom_reaper(struct task_struct *tsk)
 }
 #endif /* CONFIG_MMU */
 
+/**
+ * tsk->mm has to be non NULL and caller has to guarantee it is stable (either
+ * under task_lock or operate on the current).
+ */
+static void __mark_oom_victim(struct task_struct *tsk)
+{
+	struct mm_struct *mm = tsk->mm;
+
+	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
+		mmgrab(tsk->signal->oom_mm);
+		set_bit(MMF_OOM_VICTIM, &mm->flags);
+	}
+}
+
 /**
  * mark_oom_victim - mark the given task as OOM victim
  * @tsk: task to mark
@@ -736,18 +750,13 @@ static inline void wake_oom_reaper(struct task_struct *tsk)
  */
 static void mark_oom_victim(struct task_struct *tsk)
 {
-	struct mm_struct *mm = tsk->mm;
-
 	WARN_ON(oom_killer_disabled);
 	/* OOM killer might race with memcg OOM */
 	if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
 		return;
 
 	/* oom_mm is bound to the signal struct life time. */
-	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
+	__mark_oom_victim(tsk);
-		mmgrab(tsk->signal->oom_mm);
-		set_bit(MMF_OOM_VICTIM, &mm->flags);
-	}
 
 	/*
 	 * Make sure that the task is woken up from uninterruptible sleep
@@ -1185,3 +1194,18 @@ void pagefault_out_of_memory(void)
 	out_of_memory(&oc);
 	mutex_unlock(&oom_lock);
 }
+
+void add_to_oom_reaper(struct task_struct *p)
+{
+	p = find_lock_task_mm(p);
+	if (!p)
+		return;
+
+	get_task_struct(p);
+	if (task_will_free_mem(p)) {
+		__mark_oom_victim(p);
+		wake_oom_reaper(p);
+	}
+	task_unlock(p);
+	put_task_struct(p);
+}