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Re: [PATCH] Add support for profiling Loongson 2E

To: Dajie Tan <jiankemeng@gmail.com>
Subject: Re: [PATCH] Add support for profiling Loongson 2E
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 26 Jul 2007 12:17:03 +0100
Cc: John Levon <levon@movementarian.org>, linux-mips <linux-mips@linux-mips.org>, phil.el@wanadoo.fr, oprofile-list@lists.sourceforge.net
In-reply-to: <5861a7880707251814q4b6876a1u4291d068e201488c@mail.gmail.com>
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References: <5861a7880707240220g5d8129anc95e10bea833e323@mail.gmail.com> <20070724144051.GA17256@linux-mips.org> <5861a7880707242041w32811dal6e2765747cbada32@mail.gmail.com> <20070725125235.GD8454@totally.trollied.org.uk> <5861a7880707251814q4b6876a1u4291d068e201488c@mail.gmail.com>
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On Thu, Jul 26, 2007 at 05:14:14AM +0400, Dajie Tan wrote:

> >> Yeah,this change is to enhance the robust of oprofile. When using
> >> performace counter manually(writting control register in a module, no
> >> need to use the oprofile),I usually make kernel panic if I do not
> >> initialize the oprofile and enable the overflow interrupt carelessly.
> >> So, this change can avoid this panic. :D
> >
> >This panic is good and should stay. It shows that you've made a mistake.
> >
> >john
> >
> 
> This panic is caused by accessing a null pointer.Do you think that
> accessing a null
> pointer is allowed in a robust system ?

Of course it isn't.  From the perspective of us kernel maintainers patches
that add such checks are a red flag which raise concerns about the
correctness of the caller of the function.  So if a patch like this is
submitted the first thing that is likely to happen is that we will ask
why the check is needed.  It does not mean such a patch is fundamentally
a no-no but the code will be looked at a little harder.

  Ralf

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