linux-kernel - Re: [PATCH] usb/mcs7830: Don't use buffers from stack for USB transfers

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Message-Id: <20090120.144719.120709836.davem@davemloft.net>
Date:	Tue, 20 Jan 2009 14:47:19 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	arnd@...db.de
Cc:	ceggers@....de, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] usb/mcs7830: Don't use buffers from stack for USB
 transfers

From: Arnd Bergmann <arnd@...db.de>
Date: Tue, 20 Jan 2009 23:45:47 +0100

> On Tuesday 20 January 2009, you wrote:
> > From: Christian Eggers <christian.eggers@...hrein.de>
> > 
> > mcs7830_set_reg() and mcs7830_get_reg() are called with buffers
> > from stack which must not be used directly for USB transfers.
> > This causes corruption of the stack particulary on non x86
> > architectures because DMA may be used for these transfers.
> > 
> > Signed-off-by: Christian Eggers <christian.eggers@...hrein.de>
> 
> Have you observed problems with this, or just suspected trouble?

Yes, this is in response to SH platform failures.

You cannot DMA from/to the kernel stack, because it might not be in
the aliased linear mapping of physical memory.  It could even be
vmalloc()'d memory on some platforms.
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