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Date: Wed, 21 Aug 2013 15:10:25 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Chen Gang <gang.chen@asianux.com>
Cc: bsingharora@gmail.com,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kernel/delayacct.c: check NULL for member variable
 'delays' in all extern functions.
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On Tue, 20 Aug 2013 10:40:03 +0800 Chen Gang <gang.chen@asianux.com> wrote:

> The member variable 'delays' may be NULL, so need check NULL before use
> it for all extern functions, just like __delayacct_tsk_init() and
> __delayacct_add_tsk() have already done.

If task.delays is NULL, the kernel will oops.  I don't recall seeing
such oops reports hence I suspect that you missed some check somewhere.

For example, delayacct_blkio_start() checks current->delays before
calling __delayacct_blkio_start(), so why retest current->delays in
__delayacct_blkio_start()?