deadlock in synchronize_srcu() in debugfs?

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From	Johannes Berg <johannes@sipsolutions.net>
Newsgroups	linux.kernel
Subject	deadlock in synchronize_srcu() in debugfs?
Date	Thu, 23 Mar 2017 16:00:01 +0100
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Hi,

Before I go hunting - has anyone seen a deadlock in synchronize_srcu()
in debugfs_remove() before? We're observing that with our (backported,
but very recent) driver against 4.9 (and 4.10, I think), but there are
no backports of any debugfs things so the backport itself doesn't seem
like a likely problem.

sysrq-w shows a lot of tasks blocked on various locks (e.g. RTNL), but
the ultimate problem is the wireless stack getting blocked on
debugfs_remove_recursive(), in __synchronize_srcu(), in
wait_for_completion() (while holding lots of locks, hence the other
tasks getting stuck).

Thanks,
johannes

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deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-23 16:00 +0100
  Re: deadlock in synchronize_srcu() in debugfs? Nicolai Stange <nicstange@gmail.com> - 2017-03-23 16:40 +0100
    Re: deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-23 16:50 +0100
    Re: deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-27 14:00 +0200
  Re: deadlock in synchronize_srcu() in debugfs? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-03-23 16:40 +0100
    Re: deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-23 16:50 +0100
  Re: deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-23 16:40 +0100
    Re: deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-24 10:00 +0100
      Re: deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-24 10:30 +0100
        Re: deadlock in synchronize_srcu() in debugfs? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-03-24 18:50 +0100
          Re: deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-24 20:00 +0100
            Re: deadlock in synchronize_srcu() in debugfs? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-03-24 20:40 +0100
              Re: deadlock in synchronize_srcu() in debugfs? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-03-24 21:30 +0100
                Re: deadlock in synchronize_srcu() in debugfs? Johannes Berg <johannes@sipsolutions.net> - 2017-03-27 13:20 +0200

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