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Subject: Re: [PATCH v2 2/9] dmapool: cleanup error messages
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From: Tony Battersby <tonyb@cybernetics.com>
Message-ID: <4ed8f094-ae62-65c1-ec46-0d39b594abba@cybernetics.com>
Date: Fri, 3 Aug 2018 17:18:25 -0400
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To: Matthew Wilcox <willy@infradead.org>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>, Christoph Hellwig <hch@lst.de>, Marek Szyprowski <m.szyprowski@samsung.com>, Sathya Prakash <sathya.prakash@broadcom.com>, Chaitra P B <chaitra.basappa@broadcom.com>, Suganath Prabu Subramani <suganath-prabu.subramani@broadcom.com>, iommu@lists.linux-foundation.org, linux-mm <linux-mm@kvack.org>, linux-scsi <linux-scsi@vger.kernel.org>, MPT-FusionLinux.pdl@broadcom.com

On 08/03/2018 05:07 PM, Matthew Wilcox wrote:
> On Fri, Aug 03, 2018 at 02:43:07PM -0400, Tony Battersby wrote:
>> Out of curiosity, I just tried to create a dmapool with a NULL dev and
>> it crashed on this:
>>
>> static inline int dev_to_node(struct device *dev)
>> {
>> 	return dev->numa_node;
>> }
>>
>> struct dma_pool *dma_pool_create(const char *name, struct device *dev,
>> 				 size_t size, size_t align, size_t boundary)
>> {
>> 	...
>> 	retval = kmalloc_node(sizeof(*retval), GFP_KERNEL, dev_to_node(dev));
>> 	...
>> }
>>
>> So either it needs more special cases for supporting a NULL dev, or the
>> special cases can be removed since no one does that anyway.
> Actually, it's worse.  dev_to_node() works with a NULL dev ... unless
> CONFIG_NUMA is set.  So we're leaving a timebomb by pretending to
> allow it.  Let's just 'if (!dev) return NULL;' early in create.
>
>
Looking further down it does stuff with dev->dma_pools unconditionally
that doesn't depend on the config.A  So it would blow up on non-NUMA
also.A  So no timebomb, just an immediate kaboom.