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

To: Olaf Weber <olaf@xxxxxxx>
Subject: Re: [PATCH 1/2] fs/xfs: Drop unnecessary NULL test
From: Julia Lawall <julia@xxxxxxx>
Date: Tue, 14 Jul 2009 14:15:42 +0200 (CEST)
Cc: felixb@xxxxxxx, xfs-masters@xxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, kernel-janitors@xxxxxxxxxxxxxxx
In-reply-to: <bzy7hybzh6k.fsf@xxxxxxxxxxxxxxxxxxxx>
References: <Pine.LNX.4.64.0907131209250.6808@xxxxxxxxxxx> <bzy7hybzh6k.fsf@xxxxxxxxxxxxxxxxxxxx>
On Tue, 14 Jul 2009, Olaf Weber wrote:

> Julia Lawall writes:
> 
> > From: Julia Lawall <julia@xxxxxxx>
> > 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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