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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-mm@kvack.org, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
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        Vlastimil Babka <vbabka@suse.cz>, Hugh Dickins <hughd@google.com>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH] Revert "mm: rename _count, field of the struct page, to _refcount"
References: <1466068966-24620-1-git-send-email-vkuznets@redhat.com>
	<20160616093235.GA14640@infradead.org>
Date: Thu, 16 Jun 2016 12:30:16 +0200
In-Reply-To: <20160616093235.GA14640@infradead.org> (Christoph Hellwig's
	message of "Thu, 16 Jun 2016 02:32:35 -0700")
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Christoph Hellwig <hch@infradead.org> writes:

> On Thu, Jun 16, 2016 at 11:22:46AM +0200, Vitaly Kuznetsov wrote:
>> _count -> _refcount rename in commit 0139aa7b7fa12 ("mm: rename _count,
>> field of the struct page, to _refcount") broke kdump. makedumpfile(8) does
>> stuff like READ_MEMBER_OFFSET("page._count", page._count) and fails. While
>> it is definitely possible to fix this particular tool I'm not sure about
>> other tools which might be doing the same.
>> 
>> I suggest we remember the "we don't break userspace" rule and revert for
>> 4.7 while it's not too late.
>
> Err, sorry - this is not "userspace".  It's crazy crap digging into
> kernel internal structure.
>
> The rename was absolutely useful, so fix up your stinking pike in kdump.

Ok, sure, I'll send a patch to it. I was worried about other tools out
there which e.g. inspect /proc/vmcore. As it is something we support
some conservatism around it is justified.

-- 
  Vitaly