Messages in this thread | | | Date | Tue, 25 Aug 2009 10:40:52 +0200 | From | Ingo Molnar <> | Subject | Re: WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4), by kmemleak's scan_block() |
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* Pekka Enberg <penberg@cs.helsinki.fi> wrote:
> On Tue, 2009-08-25 at 09:27 +0100, Catalin Marinas wrote: > > On Tue, 2009-08-25 at 11:08 +0300, Pekka Enberg wrote: > > > On Tue, 2009-08-25 at 10:04 +0200, Vegard Nossum wrote: > > > > 2009/8/25 Ingo Molnar <mingo@elte.hu>: > > > > > FYI, -tip testing triggered the following kmemcheck warning in > > > > > kmemleak: > > > > > > > > > > PM: Adding info for No Bus:vcsa7 > > > > > WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4) > > > > > d873f9f600000000c42ae4c1005c87f70000000070665f666978656400000000 > > > > > i i i i u u u u i i i i i i i i i i i i i i i i i i i i i u u u > > [...] > > > > Already the patch to make kmemcheck and kmemleak mutually exclusive is > > > > underway. It is not surprising that kmemleak is scanning uninitialized > > > > memory. But if you say that you have tried it before, it is strange > > > > that it didn't appear until now. > > > > > > Why isn't it surprising? Yes, it's non-fatal for kmemleak to scan > > > uninitialized memory but we could be looking at non-initialized struct > > > member that's a bug waiting to happen elsewhere in the code (that > > > doesn't trigger often). > > > > It isn't surprising to me either. Kmemleak scans the memory periodically > > but it cannot know whether such memory was initialised or not to avoid > > scanning it. So I would expect such warnings if both kmemleak and > > kmemcheck are enabled. Scanning uninitialised memory is fine with > > kmemleak, it just increases the number of false negatives (with > > SLAB_DEBUG enabled, however, the allocated blocks are pre-initialised). > > > > So kmemleak and kmemcheck should be exclusive, unless there is a way for > > kmemleak to validate an address with kmemcheck before deciding whether > > to scan a memory block. > > It's possible. Look at the kmemcheck_shadow_lookup() and > kmemcheck_shadow_test() calls in kmemcheck_read_strict(), for > example. > > Vegard, what do you think? I think making kmemcheck and kmemleak > play nice with each other is useful for people like Ingo who do > automated testing.
There's already a couple of exclusion rules in kmemcheck:
menuconfig KMEMCHECK bool "kmemcheck: trap use of uninitialized memory" depends on DEBUG_KERNEL depends on !X86_USE_3DNOW depends on SLUB || SLAB depends on !CC_OPTIMIZE_FOR_SIZE depends on !FUNCTION_TRACER
such type of Kconfig driven exclusion is usually a somewhat lame way to express limitations in the software.
CC_OPTIMIZE_FOR_SIZE is an externality that cannot be eliminated, but the others could be improved - and we should definitely not extend the list of exclusions.
Ingo
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