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

To: Julia Lawall <julia@xxxxxxx>
Subject: Re: [PATCH 1/2] fs/xfs: Drop unnecessary NULL test
From: Olaf Weber <olaf@xxxxxxx>
Date: Tue, 14 Jul 2009 12:34:43 +0200
Cc: felixb@xxxxxxx, xfs-masters@xxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, kernel-janitors@xxxxxxxxxxxxxxx
References: <Pine.LNX.4.64.0907131209250.6808@xxxxxxxxxxx>
User-agent: Gnus/5.1007 (Gnus v5.10.7) XEmacs/21.4.3 (irix)
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.

In this particular case, there is a check for NULL and early exit in
xfs_mru_cache_create(), the function that does the INIT_DELAYED_WORK().

Olaf

> The semantic match that finds this problem is as follows:
> (http://www.emn.fr/x-info/coccinelle/)

> // <smpl>
> @@
> expression x,e;
> @@
> x = container_of(...)
> ... when != x = e
> * x == NULL
> // </smpl>

> Signed-off-by: Julia Lawall <julia@xxxxxxx>

Acked-By: Olaf Weber <olaf@xxxxxxx>

> ---
>  fs/xfs/xfs_mru_cache.c              |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)

> diff --git a/fs/xfs/xfs_mru_cache.c b/fs/xfs/xfs_mru_cache.c
> index 4b0613d..0651ce7 100644
> --- a/fs/xfs/xfs_mru_cache.c
> +++ b/fs/xfs/xfs_mru_cache.c
> @@ -280,8 +280,8 @@ _xfs_mru_cache_reap(
>       xfs_mru_cache_t         *mru = container_of(work, xfs_mru_cache_t, 
> work.work);
>       unsigned long           now, next;
 
> -     ASSERT(mru && mru->lists);
> -     if (!mru || !mru->lists)
> +     ASSERT(mru->lists);
> +     if (!mru->lists)
>               return;
 
>       spin_lock(&mru->lock);

-- 
Olaf Weber                 SGI               Phone:  +31(0)30-6696752
                           Veldzigt 2b       Fax:    +31(0)30-6696799
Technical Lead             3454 PW de Meern  Vnet:   955-7151
Storage Software           The Netherlands   Email:  olaf@xxxxxxx

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