Re: [PATCH] dma-mapping: Add BUG_ON for uninitialized dma_ops

From: Marek Szyprowski
Date: Thu Jun 13 2013 - 04:51:42 EST

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

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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