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

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: hit a KASan bug related to Perf during stress test
Date	2016-10-24 14:30 +0200
Message-ID	<svMy6-7xJ-29@gated-at.bofh.it> (permalink)
References	<svKd0-5NX-5@gated-at.bofh.it> <svKd0-5NX-3@gated-at.bofh.it> <svLsl-6Te-5@gated-at.bofh.it> <svMop-7un-5@gated-at.bofh.it>
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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;
> >  }
> >
> >  static u32 perf_event_tid(struct perf_event *event, struct task_struct *p)
>
> Should we do the same for perf_event_tid() and report -1 as the pid/tid
> in the !alive case? -1 should be an obvious invalid pid since we limit
> the pid-space to less than 32 bits.

task_pid_nr_ns() is always safe, it calls __task_pid_nr_ns(). But yes,
it can return zero if called after exit_notify() and/or release_task().

And while zero is not a valid pid too, I guess it can be confused with
the idle thread's "pid" ?

Oleg.

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Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 12:00 +0200
  Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 13:20 +0200
    Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 13:30 +0200
      Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 13:40 +0200
        Re: hit a KASan bug related to Perf during stress test Jiri Olsa <jolsa@redhat.com> - 2016-10-24 14:10 +0200
          Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 14:20 +0200
    Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 13:30 +0200
      Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 14:10 +0200
        Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 14:20 +0200
          Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 14:30 +0200
            Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 14:40 +0200
              Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 15:30 +0200
                Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 15:50 +0200
                Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 16:20 +0200
                Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 16:40 +0200
                Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 17:50 +0200
                Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 18:00 +0200
                RE: hit a KASan bug related to Perf during stress test "Ni, BaoleX" <baolex.ni@intel.com> - 2016-10-25 09:00 +0200
                Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-25 11:30 +0200
                Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-25 16:50 +0200
                Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-26 11:10 +0200
                Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-26 18:20 +0200
            Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 14:40 +0200
        Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 14:20 +0200
    Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 14:20 +0200
      Re: hit a KASan bug related to Perf during stress test Peter Zijlstra <peterz@infradead.org> - 2016-10-24 14:30 +0200
      Re: hit a KASan bug related to Perf during stress test Oleg Nesterov <oleg@redhat.com> - 2016-10-24 14:30 +0200

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