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