linux-kernel - Re: [PATCH -tip 2/5] x86: use asm-generic/dma-mapping-common.h

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Date:	Mon, 22 Jun 2009 16:22:15 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Vegard Nossum <vegard.nossum@...il.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	akpm@...ux-foundation.org, sam@...nborg.org, zippel@...ux-m68k.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip 2/5] x86: use asm-generic/dma-mapping-common.h

On Mon, 2009-06-22 at 14:10 +0100, Catalin Marinas wrote:
> On Mon, 2009-06-22 at 14:49 +0200, Ingo Molnar wrote:
> > * Vegard Nossum <vegard.nossum@...il.com> wrote:
> > > Seems to be CONFIG_DEBUG_SLAB=y that is the culprit in this case. Hm,
> > > is Kconfig busted?
> > > 
> > > lib/Kconfig.debug:301:config DEBUG_SLAB
> > > lib/Kconfig.debug-302-  bool "Debug slab memory allocations"
> > > lib/Kconfig.debug:303:  depends on DEBUG_KERNEL && SLAB && !KMEMCHECK
> > > 
> > > fujita-config:1475:CONFIG_DEBUG_SLAB=y
> > > fujita-config:1558:CONFIG_KMEMCHECK=y
> > > 
> > > ...what gives? Pekka?
> > 
> > Kmemleak introduced this piece of not so nice solution recently:
> > 
> > +config DEBUG_KMEMLEAK
> > +       bool "Kernel memory leak detector"
> > +       depends on DEBUG_KERNEL && EXPERIMENTAL && (X86 || ARM) && \
> > +               !MEMORY_HOTPLUG
> > +       select DEBUG_SLAB if SLAB
> > +       select SLUB_DEBUG if SLUB
> > +       select DEBUG_FS if SYSFS
> > +       select STACKTRACE if STACKTRACE_SUPPORT
> > +       select KALLSYMS
> > 
> > that should be a depends line, not a select line.
> 
> Kmemleak doesn't strictly need DEBUG_SLAB to make it a dependency. But
> enabling it may reduce (in theory) the false negatives by poisoning the
> allocated objects (and hence clearing any possible pointers to other
> objects). But I don't have any figures to show this is the case. I'll
> post a patch to drop those selects.
> 
> BTW, wouldn't it be feasible for kbuild to ignore the select statements
> if the selected config has unmet dependencies?

Hmm, no idea, lets cc some relevant people here. But can we remove the
select and add a config option help text to kmemleak as a short-term
solution?

			Pekka

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