linux-kernel - Re: [PATCH] x86/mm/hotplug: fix BUG_ON() after hotremove by not freeing pud v2

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Message-ID: <20170607170651.exful7yvxvrjaolz@node.shutemov.name>
Date:   Wed, 7 Jun 2017 20:06:51 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     jglisse@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: Re: [PATCH] x86/mm/hotplug: fix BUG_ON() after hotremove by not
 freeing pud v2

On Wed, Jun 07, 2017 at 08:03:25PM +0300, Kirill A. Shutemov wrote:
> On Wed, Jun 07, 2017 at 10:46:20AM -0400, 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()
> > 
> > Changed since v1:
> >   - make free_pud() conditional on the number of page table
> >     level
> >   - improved commit message
> > 
> > Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> > Cc: Andy Lutomirski <luto@...nel.org>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > Cc: Logan Gunthorpe <logang@...tatee.com>
> > > thus we now trigger a BUG_ON() l128 in sync_global_pgds()
> > >
> > > This patch remove free_pud() like in af2cf278ef4f
> > ---
> >  arch/x86/mm/init_64.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> > index 95651dc..61028bc 100644
> > --- a/arch/x86/mm/init_64.c
> > +++ b/arch/x86/mm/init_64.c
> > @@ -771,6 +771,16 @@ static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
> >  	spin_unlock(&init_mm.page_table_lock);
> >  }
> >  
> > +/*
> > + * For 4 levels page table we do not want to free puds but for 5 levels
> > + * we should free them. This code also need to change to adapt for boot
> > + * time switching between 4 and 5 level.
> > + */
> > +#if CONFIG_PGTABLE_LEVELS == 4
> > +static inline void free_pud_table(pud_t *pud_start, p4d_t *p4d)
> > +{
> > +}
> 
> Just "if (CONFIG_PGTABLE_LEVELS > 4)" before calling free_pud_table(), but
> okay -- I'll rework it anyway for boot-time switching.

Err. "if (CONFIG_PGTABLE_LEVELS == 4)" obviously.

-- 
 Kirill A. Shutemov