linux-kernel - Re: lockdep problem conversion semaphore->mutex (dev->sem)

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Message-ID: <3efb10970712081255k7ceec2bev4932512b2e1cda89@mail.gmail.com>
Date:	Sat, 8 Dec 2007 21:55:54 +0100
From:	"Remy Bohmer" <linux@...mer.net>
To:	"Peter Zijlstra" <peterz@...radead.org>
Cc:	"Daniel Walker" <dwalker@...sta.com>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Dave Chinner" <dgc@....com>
Subject: Re: lockdep problem conversion semaphore->mutex (dev->sem)

Peter,

Thanks for this clear answer.

Remy

2007/12/8, Peter Zijlstra <peterz@...radead.org>:
>
> On Sat, 2007-12-08 at 21:33 +0100, Remy Bohmer wrote:
>
> > Which problems? I did not see any special things, it looked rather
> > straight forward. What have I overlooked?
>
> On suspend it locks the whole device tree, this means it has 'unbounded'
> nesting and holds an 'unbounded' number of locks. Neither things are
> easy to annotate (remember that mutex_lock_nested can handle up to 8
> nestings and current->held_locks has a max of 30).
>
> In fact, converting this will be the hardest part, it would require
> reworking the locking and introduction of a hard limit on the device
> tree depth - this might upset some people, but I suspect that 16 or 24
> should be deep enough for pretty much anything. Of course, if people
> prove me wrong, I'll have to reconsider. The up-side of the locking
> scheme I'm thinking of will be that locking the whole tree will only
> take 'depth' number of opterations vs the total number of tree elements.
>
>
>
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