linux-kernel - Re: kmemleak: Protect the seq start/next/stop sequence byrcu_read

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Message-ID: <20090813094437.GB22762@elte.hu>
Date:	Thu, 13 Aug 2009 11:44:37 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: kmemleak: Protect the seq start/next/stop sequence
	byrcu_read_lock()


* Catalin Marinas <catalin.marinas@....com> wrote:

> On Thu, 2009-08-13 at 08:52 +0200, Ingo Molnar wrote:
> > * Catalin Marinas <catalin.marinas@....com> wrote:
> > 
> > > On Wed, 2009-08-12 at 21:52 +0100, Ingo Molnar wrote:
> > > > * Catalin Marinas <catalin.marinas@....com> wrote:
> > > > 
> > > > > kmemleak: Allow rescheduling during an object scanning
> > > > 
> > > > i tried this in -tip testing, and it crashes quickly:
> > > > 
> > > > [   81.900051] BUG: unable to handle kernel paging request at ffff880020000000
> > > > [   81.901382] IP: [<ffffffff8112ae7e>] scan_block+0xee/0x190
> > > 
> > > It looks like my check for object->flags & OBJECT_ALLOCATED in 
> > > scan_object() may not be enough.
> > > 
> > > I'm a bit confused as the config you sent says x86_32 but the 
> > > fault address above looks like a 64 bit one (and my knowledge 
> > > of x86 isn't great). Is this x86_64?
> > 
> > ahm indeed. It crashed not straight during bootup but while my 
> > tests built the next kernel iteration already (with a new random 
> > config),
> 
> Looking through the code and documentation, the fault address 
> above seems to be the directly mapped RAM. Do you have 512MB of 
> RAM or less on your machine? Or is there a hole in the virtual 
> space at that point?

i still have the full crashlog (attached below) - you can see all 
the mappings (and other details) in that.

It's a fairly regular whitebox PC with 1GB of RAM:

[    0.000000] initial memory mapped : 0 - 20000000
[    0.000000] init_memory_mapping: 0000000000000000-000000003fff0000
[    0.000000]  0000000000 - 003fe00000 page 2M
[    0.000000]  003fe00000 - 003fff0000 page 4k
[    0.000000] kernel direct mapping tables up to 3fff0000 @ 10000-13000

	Ingo

View attachment "crash.log" of type "text/plain" (154832 bytes)