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Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc
Date 2016-01-20 12:50 +0100
Message-ID <qSZqV-5Mi-9@gated-at.bofh.it> (permalink)
References <qLmum-5sY-15@gated-at.bofh.it> <qR7sC-2Y8-13@gated-at.bofh.it> <qRfzR-gk-31@gated-at.bofh.it> <qRgme-OC-7@gated-at.bofh.it> <qSXp9-4uM-25@gated-at.bofh.it>
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On Wed, Jan 20, 2016 at 10:36:01AM +0100, Dmitry Vyukov wrote:

> +Peter, Ingo, can you please suggest a way to annotate this locking
> pattern to avoid lockdep false positive?

No, because I haven't a clue what the actual problem is.

The report is fairly clear on how:

 routelock
   &port->buf.lock/1
     &o_tty->termios_rwsem/1
       &buf->lock

gets established, and shows where we try:

  &buf->lock
    routelock

Which gives a circle, ergo deadlock.

Show which link is wrong and why, and I can suggest ways of annotating
that.

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Thread

Re: tty: deadlock between n_tracerouter_receivebuf and  flush_to_ldisc One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-01-15 17:40 +0100
  Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc Dmitry Vyukov <dvyukov@google.com> - 2016-01-15 18:30 +0100
    Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc Dmitry Vyukov <dvyukov@google.com> - 2016-01-20 10:40 +0100
      Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc Peter Zijlstra <peterz@infradead.org> - 2016-01-20 12:50 +0100
        Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc Dmitry Vyukov <dvyukov@google.com> - 2016-01-20 13:00 +0100
          Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc Peter Zijlstra <peterz@infradead.org> - 2016-01-20 13:10 +0100
            Re: tty: deadlock between n_tracerouter_receivebuf and  flush_to_ldisc One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-01-20 16:00 +0100
              Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc Dmitry Vyukov <dvyukov@google.com> - 2016-01-20 16:20 +0100
                Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc Peter Zijlstra <peterz@infradead.org> - 2016-01-20 17:40 +0100
  Re: tty: deadlock between n_tracerouter_receivebuf and  flush_to_ldisc J Freyensee <james_p_freyensee@linux.intel.com> - 2016-01-20 03:10 +0100

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