linux-kernel - Re: [PATCH] x86/mm/hotplug: fix BUG_ON() after hotremove by not freeing pud v3

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Message-ID: <20170626094304.bmvsia5zpixbazpu@gmail.com>
Date:   Mon, 26 Jun 2017 11:43:04 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     jglisse@...hat.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86/mm/hotplug: fix BUG_ON() after hotremove by not
 freeing pud v3


* jglisse@...hat.com <jglisse@...hat.com> wrote:

> From: Jérôme Glisse <jglisse@...hat.com>
> 
> With commit af2cf278ef4f we no longer free pud so that we do not
> have synchronize all pgd on hotremove/vfree. But the new 5 level
> page table patchset reverted that for 4 level page table.
> 
> This patch restore af2cf278ef4f and disable free_pud() if we are
> in the 4 level page table case thus avoiding BUG_ON() after hot-
> remove.
> 
> af2cf278ef4f x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()

Am I correct that the _real_ buggy commit that introduced the breakage in v4.12 
is:

  f2a6a7050109: ("x86: Convert the rest of the code to support p4d_t")

... right?

Thanks,

	Ingo