linux-kernel - Re: [PATCH 2/4] kmemleak: Handle percpu memory allocation

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Date:	Thu, 29 Sep 2011 12:57:11 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Catalin Marinas <catalin.marinas@....com>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Huajun Li <huajun.li.lee@...il.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 2/4] kmemleak: Handle percpu memory allocation

On Thu, 29 Sep 2011, Catalin Marinas wrote:

> A better approach would be to tell kmemleak about the __percpu pointer
> via some additional API (or some other way to detect that it's a
> __percpu pointer) and kmemleak would do the for_each_possible_cpu()
> conversion when scanning.
>
> The question - can we guarantee that the __percpu pointer returned by
> alloc_percpu() does not overlap with some memory block allocated
> elsewhere? At least for the first chunk it seems to overlap with the
> percpu data section, which is fine as that's not added in kmemleak as an
> allocated block.

percpu data can be placed in physical areas as well as virtually mapped
areas. The size of the offset returned by alloc_percpu() depends on the
mechanism and therefore is treated like an arbitrary value.

> Allowing overlapping blocks in kmemleak may be a solution but it's not
> implemented yet.

You could use the address of the instance of the percpu variable in the
*first* cpu as the canonical item. As soon as you calculate an actual
address (using a processor number) you will have a physical address that
cannot overlap elsewhere.
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