linux-kernel - Re: BUG: NULL pointer dereference at 00000000 -- IP: [<f8e783d5>] :b43:b43_dma_mapping

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Date:	Tue, 10 Jun 2008 16:34:21 +0200
From:	Michael Buesch <mb@...sch.de>
To:	"Vegard Nossum" <vegard.nossum@...il.com>
Cc:	"Miles Lane" <miles.lane@...il.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: BUG: NULL pointer dereference at 00000000 -- IP: [<f8e783d5>] :b43:b43_dma_mapping_error+0x16/0x155

On Tuesday 10 June 2008 16:29:17 Vegard Nossum wrote:
> On Tue, Jun 10, 2008 at 4:23 PM, Michael Buesch <mb@...sch.de> wrote:
> > On Tuesday 10 June 2008 16:09:37 Miles Lane wrote:
> >> BUG: unable to handle kernel NULL pointer dereference at 00000000
> >> IP: [<f8e783d5>] :b43:b43_dma_mapping_error+0x16/0x155
> >
> >
> > It seems to crash at
> >  60 extern const struct dma_mapping_ops *dma_ops;
> >  61
> >  62 static inline int dma_mapping_error(dma_addr_t dma_addr)
> >  63 {
> >  64         if (dma_ops->mapping_error)
> >  65                 return dma_ops->mapping_error(dma_addr);
> >  66
> >  67         return (dma_addr == bad_dma_address);
> >  68 }
> 
> No, this is wrong.
> 
> /* Check if a DMA mapping address is invalid. */
> static bool b43_dma_mapping_error(struct b43_dmaring *ring,
>                                   dma_addr_t addr,
>                                   size_t buffersize, bool dma_to_device)
> {
>         if (unlikely(dma_mapping_error(ring->dev->dev->dma_dev, addr)))
> 
> It crashes on this line ---^

Which calls dma_mapping_error(), correct?

But you are right. I see the bug now.
ring->dev is assigned after the call.
I wonder why it works reliably on all of my machines.

-- 
Greetings Michael.
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