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

[Jerome Glisse]

On Mon, Jun 26, 2017 at 11:43:04AM +0200, Ingo Molnar wrote:
> 
> * jglisse@xxxxxxxxxx <jglisse@xxxxxxxxxx> wrote:
> 
> > From: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > 
> > 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