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Groups > linux.kernel > #1507107

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

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: hit a KASan bug related to Perf during stress test
Date 2016-10-24 13:30 +0200
Message-ID <svLC2-6Wt-7@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>
Organization linux.* mail to news gateway

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On Mon, Oct 24, 2016 at 01:15:27PM +0200, Oleg Nesterov wrote:
> On 10/24, Peter Zijlstra wrote:
> >
> > > [32738.867020]  [<ffffffff810d9975>] task_tgid_nr_ns+0x35/0xb0
> >
> > So here we did: perf_event_[pt]id(event, current);
> >
> > How can _current_ not be valid anymore?
> 
> ...
> 
> > > [32739.040207]  [<ffffffff81135a4c>] __call_rcu+0x12c/0x450
> >
> > And while we just called release_task(), that call_rcu() should still be
> > pending at this point,
> 
> Yes, current is still valid.
> 
> But nothing protects current->group_leader or parent/real_parent, they
> can point to the exited/freed task. We really need to nullify them in
> __unhash_process() to catch the problems like this, I wanted to do this
> many times...
> 
> So you simply can't know your tgid or even tid after release_task() calls
> __unhash_process(). Actually after exit_notify() unless the exiting task
> autoreaps itself.
> 
> How about the trivial fix below?
> 
> Oleg.
> 
> --- 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.

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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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