Re: [LKP] [mm, oom] c1e4c54f9c: BUG:KASAN:null-ptr-deref_in_d

[David Rientjes]

On Mon, 6 Aug 2018, çèé wrote:

> Hi Michal
> Sorry, I cannot open the link you shared.
> 

The suggestion atop your previous patch was

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -438,14 +438,6 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
 
 	dump_stack();
 
-	/* one line summary of the oom killer context. */
-	pr_info("oom-kill:constraint=%s,nodemask=%*pbl",
-			oom_constraint_text[oc->constraint],
-			nodemask_pr_args(oc->nodemask));
-	cpuset_print_current_mems_allowed();
-	mem_cgroup_print_oom_context(oc->memcg, p);
-	pr_cont(",task=%s,pid=%d,uid=%d\n", p->comm, p->pid,
-		from_kuid(&init_user_ns, task_uid(p)));
 	if (is_memcg_oom(oc))
 		mem_cgroup_print_oom_meminfo(oc->memcg);
 	else {
@@ -836,7 +828,8 @@ static bool task_will_free_mem(struct task_struct *task)
 	return ret;
 }
 
-static void __oom_kill_process(struct task_struct *victim)
+static void __oom_kill_process(struct task_struct *victim,
+			       struct oom_control *oc)
 {
 	struct task_struct *p;
 	struct mm_struct *mm;
@@ -883,6 +876,18 @@ static void __oom_kill_process(struct task_struct *victim)
 		K(get_mm_counter(victim->mm, MM_ANONPAGES)),
 		K(get_mm_counter(victim->mm, MM_FILEPAGES)),
 		K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
+
+	if (oc) {
+		/* One line summary for non-group oom kills */
+		pr_info("oom-kill: constraint=%s, nodemask=%*pbl",
+			oom_constraint_text[oc->constraint],
+			nodemask_pr_args(oc->nodemask));
+		cpuset_print_current_mems_allowed();
+		mem_cgroup_print_oom_context(oc->memcg, victim);
+		pr_cont(", task=%s, pid=%d, uid=%d\n",
+			victim->comm, victim->pid,
+			from_kuid(&init_user_ns, task_uid(victim)));
+	}
 	task_unlock(victim);
 
 	/*
@@ -986,13 +991,13 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 	}
 	read_unlock(&tasklist_lock);
 
-	__oom_kill_process(victim);
+	__oom_kill_process(victim, oc);
 }
 
 static int oom_kill_memcg_member(struct task_struct *task, void *unused)
 {
 	get_task_struct(task);
-	__oom_kill_process(task);
+	__oom_kill_process(task, NULL);
 	return 0;
 }
 
@@ -1020,7 +1025,7 @@ static bool oom_kill_memcg_victim(struct oom_control *oc)
 		    oc->chosen_task == INFLIGHT_VICTIM)
 			goto out;
 
-		__oom_kill_process(oc->chosen_task);
+		__oom_kill_process(oc->chosen_task, oc);
 	}
 
 out:


You should be able to find this in your email.  We don't want to emit the 
line when a victim is not chosen.  I also did a couple of cleanups like 
spaces between commas.