linux-kernel - Re: [PATCH RFC 00/11] lock monitor: Separate features related to lock

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Date:	Tue, 23 Mar 2010 16:45:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	linux-kernel@...r.kernel.org, h.mitake@...il.com,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Jason Baron <jbaron@...hat.com>
Subject: Re: [PATCH RFC 00/11] lock monitor: Separate features related to
 lock

On Wed, 2010-03-17 at 16:39 +0100, Frederic Weisbecker wrote:
> 
> might_lock_read() uses might_fault(), rcu, workqueues and probably
> yet some others use sequences of lock_acquire/lock_release to prove
> locking while there is actually no real lock operation involved, but
> this is to detect dependency/balance mistakes. 

might_fault() simply always takes the mmap_sem because actually hitting
the fault path (which otherwise would establish that relation) is very
rare for some cases, so by forcing that dependency we get better
coverage.

rcu_read_lock() is an actual lock :-)

workqueues use 'fake' locks to connect lock chains to flush, so that we
can detect things like trying to flush a workqueue while holding a lock
that is required to complete the work.


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