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

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Date:   Wed,  7 Jun 2017 10:46:20 -0400
From:   jglisse@...hat.com
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: [PATCH] x86/mm/hotplug: fix BUG_ON() after hotremove by not freeing pud v2

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)
+{
+}
+#else /* CONFIG_PGTABLE_LEVELS == 4 */
 static void __meminit free_pud_table(pud_t *pud_start, p4d_t *p4d)
 {
 	pud_t *pud;
@@ -788,6 +798,7 @@ static void __meminit free_pud_table(pud_t *pud_start, p4d_t *p4d)
 	p4d_clear(p4d);
 	spin_unlock(&init_mm.page_table_lock);
 }
+#endif /* CONFIG_PGTABLE_LEVELS == 4 */
 
 static void __meminit
 remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
-- 
2.7.5