linux-kernel - Re: [PATCH] powerpc/kvm: silence kmemleak false positives

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Message-ID: <20200512141723.GB14943@gaia>
Date:   Tue, 12 May 2020 15:17:23 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Qian Cai <cai@....pw>
Cc:     Michael Ellerman <mpe@...erman.id.au>, paulus@...abs.org,
        benh@...nel.crashing.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/kvm: silence kmemleak false positives

On Mon, May 11, 2020 at 07:43:30AM -0400, Qian Cai wrote:
> On May 11, 2020, at 7:15 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
> > There is kmemleak_alloc_phys(), which according to the docs can be used
> > for tracking a phys address.
> > 
> > Did you try that?
> 
> Catalin, feel free to give your thoughts here.
> 
> My understanding is that it seems the doc is a bit misleading.
> kmemleak_alloc_phys() is to allocate kmemleak objects for a physical
> address range, so  kmemleak could scan those memory pointers within
> for possible referencing other memory. It was only used in memblock so
> far, but those new memory allocations here contain no reference to
> other memory.
> 
> In this case, we have already had kmemleak objects for those memory
> allocation. It is just that other pointers reference those memory by
> their physical address which is a known kmemleak limitation won’t be
> able to track the the connection. Thus, we always use
> kmemleak_ignore() to not reporting those as leaks and don’t scan those
> because they do not contain other memory reference.

Indeed. I replied directly to Michael along the same lines.

-- 
Catalin