linux-kernel - Re: [PATCH 4/7] ufs: remove the BKL

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Message-ID: <20110302144705.GA15482@elliptictech.com>
Date:	Wed, 2 Mar 2011 09:47:05 -0500
From:	Nick Bowler <nbowler@...iptictech.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org,
	Evgeniy Dushistov <dushistov@...l.ru>,
	Nick Piggin <npiggin@...il.com>
Subject: Re: [PATCH 4/7] ufs: remove the BKL

On 2011-03-02 00:13 +0100, Arnd Bergmann wrote:
> This introduces a new per-superblock mutex in UFS to replace
> the big kernel lock. I have been careful to avoid nested
> calls to lock_ufs and to get the lock order right with
> respect to other mutexes, in particular lock_super.
> 
> I did not make any attempt to prove that the big kernel
> lock is not needed in a particular place in the code,
> which is very possible.
> 
> The code is still only compile-tested,

This isn't true anymore; I've been running with this patch (well, the
previous versions thereof) for some time now.  On the other hand, I
don't use all of this driver's features.

> but it should at least be harmless on non-SMP systems, since the new
> mutex is not taken on those.

I think this part of the patch is strange.  It seems like a gratuitous
difference between SMP/preempt and other systems to #if out the code
that takes the mutex.  This might make problems with the conversion fly
under the radar longer because people with older systems won't encounter
them.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)
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