Re: hit a KASan bug related to Perf during stress test

[Oleg Nesterov]

On 10/24, Peter Zijlstra wrote:
>
> On Mon, Oct 24, 2016 at 01:15:27PM +0200, Oleg Nesterov wrote:
> >
> > --- x/kernel/events/core.c
> > +++ x/kernel/events/core.c
> > @@ -1257,7 +1257,7 @@ static u32 perf_event_pid(struct perf_ev
> >  	if (event->parent)
> >  		event = event->parent;
> >
> > -	return task_tgid_nr_ns(p, event->ns);
> > +	return pid_alive(p) ? task_tgid_nr_ns(p, event->ns) : 0;
> >  }
>
> Hurm.. should we not push this into task_tgid_nr_ns() ? I mean, now the
> user needs to be aware of this dinky detail.

Perhaps. Or into task_tgid(). Or even the patch below, __task_pid_nr_ns()
is always safe. This certainly needs some cleanups.

Oleg.

--- x/include/linux/pid.h
+++ x/include/linux/pid.h
@@ -8,7 +8,8 @@ enum pid_type
 	PIDTYPE_PID,
 	PIDTYPE_PGID,
 	PIDTYPE_SID,
-	PIDTYPE_MAX
+	PIDTYPE_MAX,
+	PIDTYPE_TGID	/* do not use */
 };
 
 /*
--- x/kernel/pid.c
+++ x/kernel/pid.c
@@ -538,7 +538,7 @@ EXPORT_SYMBOL(__task_pid_nr_ns);
 
 pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
 {
-	return pid_nr_ns(task_tgid(tsk), ns);
+	return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns);
 }
 EXPORT_SYMBOL(task_tgid_nr_ns);