Message-id: <51B98812.80201@samsung.com>
Date: Thu, 13 Jun 2013 10:51:30 +0200
From: Marek Szyprowski <m.szyprowski@samsung.com>
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To: Arnd Bergmann <arnd@arndb.de>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Michal Simek <michal.simek@xilinx.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michal Simek <monstr@monstr.eu>,
        Linux-Arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH] dma-mapping: Add BUG_ON for uninitialized dma_ops
References: <f35c5051a207b0a117f2fff27365d0ea892d1610.1370263476.git.michal.simek@xilinx.com>
 <51B703D7.8050804@samsung.com> <1370958858.2286.5.camel@dabdike>
 <201306121706.39368.arnd@arndb.de>
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On 6/12/2013 5:06 PM, Arnd Bergmann wrote:
> On Tuesday 11 June 2013, James Bottomley wrote:
> > Really, no, it's not a good idea at all.  It invites tons of patches
> > littering the code with BUG_ONs where we might possibly get a NULL
> > dereference.  All it does is add extra instructions to a code path for
> > no actual benefit.
> >
> > If you can answer the question: what more information does the BUG_ON
> > give you than the NULL deref Oops would not? then it might be
> > reasonable.
>
> The question is if a user can trigger the NULL dereference intentionally,
> in which case they might get the kernel to jump into a  user-provided
> buffer.

I don't any possibility for userspace to alter the ops pointer, so if you
think that BUG_ON() approach causes additional overhead then I'm fine to
remove it.

Best regards
-- 
Marek Szyprowski
Samsung R&D Institute Poland


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