netdev - [PATCH 0/2] sysctl: lockdep support.

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Message-ID: <m1iqm3xr2n.fsf_-_@fess.ebiederm.org>
Date:	Sat, 21 Mar 2009 00:39:28 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Jan Beulich <jbeulich@...ell.com>,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, Gautham R Shenoy <ego@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Alexey Dobriyan <adobriyan@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH 0/2] sysctl: lockdep support.

The problem:  There is a class of deadlocks that we currently
have in the kernel that lockdep does not recognize. 

In particular with the network stack we can have:

rtnl_lock();                         use_table();
unregister_netdevice();              rtnl_lock();
unregister_sysctl_table();           ....
wait_for_completion();               rtnl_lock();
....                                 unuse_table()
rtnl_unlock();                       complete();

Where we never make it to the lines labled ....

My patch following patches treats the sysctl use count as a read/writer
lock for purposes of lockdep.

The code works but I'm not certain I have plugged into lockdep quite
correctly.

Eric

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