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

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Date:   Mon, 24 Oct 2016 14:10:31 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Ni, BaoleX" <baolex.ni@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "Liu, Chuansheng" <chuansheng.liu@...el.com>
Subject: Re: hit a KASan bug related to Perf during stress test

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);