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

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Date:	Wed, 12 Aug 2009 23:16:15 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Ingo Molnar <mingo@...e.hu>
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()

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?

Anyway, does the virtual address above happen to be in the vmalloc
range? The kmemleak_free() callback for vfree() is run before __vunmap()
is executed and the OBJECT_ALLOCATED bit should be cleared.

If it's not vmalloc, do you know what else could be at that virtual
address which may be unmapped without first calling kmemleak_free()?

I've been testing the patch on both x86_32 and ARM and seemed fine (more
intensively on the latter, though obviously not exactly with the same
config as yours but as close as possible).

Thanks.

-- 
Catalin

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