linux-kernel - Re: [PATCH 1/2] fs/xfs: Drop unnecessary NULL test

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Message-ID: <Pine.LNX.4.64.0907141412550.456@ask.diku.dk>
Date:	Tue, 14 Jul 2009 14:15:42 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Olaf Weber <olaf@....com>
Cc:	felixb@....com, xfs-masters@....sgi.com, xfs@....sgi.com,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/2] fs/xfs: Drop unnecessary NULL test

On Tue, 14 Jul 2009, Olaf Weber wrote:

> Julia Lawall writes:
> 
> > From: Julia Lawall <julia@...u.dk>
> > The result of container_of should not be NULL.  In particular, in this case
> > the argument to the enclosing function has passed though INIT_DELAYED_WORK,
> > which dereferences it, implying that its container cannot be NULL.
> 
> Given the defn of container_of() it seems clear that neither its input
> pointer nor its result should ever be NULL.

container_of just does pointer arithmetic.  The result of that arithmetic 
can be NULL, ie if the argument was obtained from an expression of the 
form &x->f where x was NULL.  But in principle, values should be checked 
for NULL beforehand.

julia
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