linux-kernel - Re: atmel-mci causes kernel panic when CONFIG_DEBUG

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Date:	Thu, 19 May 2011 20:25:15 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Ludovic Desroches <ludovic.desroches@...el.com>,
	linux-mm@...ck.org, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	linux-arm-kernel@...ts.infradead.org,
	"Ferre, Nicolas" <Nicolas.FERRE@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: atmel-mci causes kernel panic when CONFIG_DEBUG_VM is set

Hello,

On Thu, May 19, 2011 at 09:53:12AM +0200, Ludovic Desroches wrote:
> There is a bug with the atmel-mci driver when the debug feature
> CONFIG_DEBUG_VM is set.
for the new audience: the driver does the following:

	flush_dcache_page(sg_page(sg));

with sg being a struct scatterlist * provided by the caller of the
struct mmc_host_ops.request callback.

> Into the atmci_read_data_pio function we use flush_dcache_page (do
> we really need it?) which call the page_mapping function where we
> can find VM_BUG_ON(PageSlab(Page)). Then a kernel panic happens.
> 
> I don't understand the purpose of the VM_BUG_ON(PageSlab(Page)) (the
> page comes from a scatter list). How could I correct this problem?
I discussed this problem with Steven and Peter on irc and Steven found
two functions in the mmc code (mmc_send_cxd_data and mmc_send_bus_test)
that use the following idiom:

	struct scatterlist sg;
	void *data_buf;

	data_buf = kmalloc(len, GFP_KERNEL);

	sg_init_one(&sg, data_buf, len);

Is that allowed (i.e. pass  kmalloc'd memory to sg_init_one)? That might
be the source of the slub page in the scatterlist, no?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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