linux-kernel - Re: [PATCH 05/17] fs: icache lock i

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Message-Id: <20100930232339.32ed3b38.akpm@linux-foundation.org>
Date:	Thu, 30 Sep 2010 23:23:39 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Dave Chinner <david@...morbit.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/17] fs: icache lock i_count

On Fri, 1 Oct 2010 02:16:02 -0400 Christoph Hellwig <hch@...radead.org> wrote:

> On Thu, Sep 30, 2010 at 11:04:16PM -0700, Andrew Morton wrote:
> > No, we've run into problems *frequently*.  A common case is where we
> > convert a mutex to a spinlock or vice versa.  If you don't rename the
> > lock, the code still compiles (with warnings) and crashes horridly at
> > runtime.
> 
> Sorry, if you run code with that obvious warnings you beg for trouble.
> If you really believe your advanced users arw too stupid to read
> compiler warnings enforcing -Werror is for sure better than obsfucating
> the code.

Well, it has happened, fairly regularly.  A common scenario is where
someone has done a conversion in one tree and someone else has touched
overlapping code in another tree and when the two meet in linux-next,
splat.  Renaming the field simply eliminates this.

Of course, the warnings don't get noticed because of the enormous
warning storm which a kernel build produces (generally much worse on
non-x86, btw).

Another reason for remaining a field is when we desire that it
henceforth be accessed via accessor functions - renaming it will
reliably break any unconverted code.
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