linux-kernel - deadlock in synchronize

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Date:   Thu, 23 Mar 2017 15:54:46 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     linux-kernel <linux-kernel@...r.kernel.org>
Cc:     Nicolai Stange <nicstange@...il.com>,
        "Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
        gregkh <gregkh@...uxfoundation.org>
Subject: deadlock in synchronize_srcu() in debugfs?

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