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

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Date:   Mon, 26 Jun 2017 10:49:34 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
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

On Mon, Jun 26, 2017 at 11:43:04AM +0200, Ingo Molnar wrote:
> 
> * 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?

Correct.

Jérôme