linux-kernel - Re: kmemleak: Unable to handle kernel paging request

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Message-Id: <D9560F26-D206-4423-ACA4-31342A73B5F9@arm.com>
Date:	Sat, 14 Jun 2014 13:05:18 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Denis Kirjanov <kda@...ux-powerpc.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: kmemleak: Unable to handle kernel paging request

On 13 Jun 2014, at 22:44, Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> On Fri, 2014-06-13 at 09:56 +0100, Catalin Marinas wrote:
> 
>> OK, so that's the DART table allocated via alloc_dart_table(). Is
>> dart_tablebase removed from the kernel linear mapping after allocation?
> 
> Yes.
> 
>> If that's the case, we need to tell kmemleak to ignore this block (see
>> patch below, untested). But I still can't explain how commit
>> d4c54919ed863020 causes this issue.
>> 
>> (also cc'ing the powerpc list and maintainers)
> 
> We remove the DART from the linear mapping because it has to be mapped
> non-cachable and having it in the linear mapping would cause cache
> paradoxes. We also can't just change the caching attributes in the
> linear mapping because we use 16M pages for it and 970 CPUs don't
> support cache-inhibited 16M pages :-( And due to the MMU segmentation
> model, we also can't mix & match page sizes in that area.
> 
> So we just unmap it, and ioremap it elsewhere.

OK, thanks for the explanation. So the kmemleak annotation makes sense.

Would you please take the I patch earlier (I guess with Denis’ tested-
by). I can send it separately if more convenient.

Thanks,

Catalin--
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