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

[Oleg Nesterov]

On 10/24, Oleg Nesterov wrote:
>
> 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.

the patch was obviously incomplete.

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
@@ -526,8 +526,11 @@ pid_t __task_pid_nr_ns(struct task_struc
        if (!ns)
                ns = task_active_pid_ns(current);
        if (likely(pid_alive(task))) {
-               if (type != PIDTYPE_PID)
+               if (type != PIDTYPE_PID) {
+                       if (type == PIDTYPE_TGID)
+                               type = PIDTYPE_PID;
                        task = task->group_leader;
+               }
                nr = pid_nr_ns(rcu_dereference(task->pids[type].pid), ns);
        }
        rcu_read_unlock();
@@ -538,7 +541,7 @@ 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);