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Date:   Wed, 18 Apr 2018 03:47:03 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Jacopo Mondi <jacopo+renesas@jmondi.org>
Cc:     ysato@users.sourceforge.jp, dalias@libc.org,
        thomas.petazzoni@free-electrons.com, robin.murphy@arm.com,
        geert@linux-m68k.org, linux-renesas-soc@vger.kernel.org,
        linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sh: mm: Fix unprotected access to struct device
Message-ID: <20180418104703.GA12462@infradead.org>
References: <1523972123-5700-1-git-send-email-jacopo+renesas@jmondi.org>
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On Tue, Apr 17, 2018 at 03:35:23PM +0200, Jacopo Mondi wrote:
> With commit ce88313069c36eef80f21fd7 ("arch/sh: make the DMA mapping
> operations observe dev->dma_pfn_offset") the generic DMA allocation
> function on which the SH 'dma_alloc_coherent()' function relies on,
> access the 'dma_pfn_offset' field of struct device.
> 
> Unfortunately the 'dma_generic_alloc_coherent()' function is called from
> several places with a NULL struct device argument, halting the CPU
> during the boot process.
> 
> This patch fixes the issue protecting access to dev->dma_pfn_offset,
> with a trivial check for validity. It also passes a valid 'struct device'
> in the 'platform_resource_setup_memory' function which is the main user
> of 'dma_alloc_coherent()', and inserting a WARN_ON() check to make future
> (and existing) bogus users of this function they're should provide a valid
> 'struct device' whenever possible.

Please fix those callers to not pass a NULL pointer instead.