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

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Date:	Sat, 8 Dec 2007 21:33:02 +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)

Hello Peter,

> And while you might not see it in-tree anymore, lockdep does help out
> tremendously while developing new code. I'm sure that without it the
> locking would be in a much worse state than it is today.

I am not arguing that, I am also convinced it has done a good job.

> I have a good idea on how to annotate this, but not yet the time to do
> so.

Sounds good...

> Aside from the nesting problems, the dev->sem has other problems as
> well. Converting this is rather non-trivial.

Which problems? I did not see any special things, it looked rather
straight forward. What have I overlooked?

> I'd not put it as harshly as you put it though, lockdep makes some
> assumptions which can lead to false positives -

By putting it this black and white, it usually helps to get all the
opinions clear ;-)
(By staying in the middle, everybody usually tend to agree ;-)

> otoh these assumptions
> often end up pointing out 'curious' locking coupled to 'curious' data
> structures. And fixing up these things often leads to better and simpler
> code.
> The emphasis is on often, this is one of the cases where this is not so.
> So while it does restain the creativity of locking it often ends up
> being for the better.

Ack.

Kind Regards,

Remy
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