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

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Message-ID: <20170607170325.65ex46hoqjalprnu@black.fi.intel.com>
Date:   Wed, 7 Jun 2017 20:03:25 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     jglisse@...hat.com
Cc:     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 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.

-- 
 Kirill A. Shutemov