[PATCH V1 5.4.y 0/2] Fix bad pmd due to race between change_prot_numa() and THP migration

[PATCH V1 5.4.y 0/2] Fix bad pmd due to race between change_prot_numa() and THP migration

[Harry Yoo]

# TL;DR

previous discussion: https://lore.kernel.org/linux-mm/20250921232709.1608699-1-harry.yoo@oracle.com/

A "bad pmd" error occurs due to race condition between
change_prot_numa() and THP migration. The mainline kernel does not have
this bug as commit 670ddd8cdc fixes the race condition. 6.1.y, 5.15.y,
5.10.y, 5.4.y are affected by this bug. 

Fixing this in -stable kernels is tricky because pte_map_offset_lock()
has different semantics in pre-6.5 and post-6.5 kernels. I am trying to
backport the same mechanism we have in the mainline kernel.

# Testing

I verified that the bug described below is not reproduced anymore
(on a downstream kernel) after applying this patch series. It used to
trigger in few days of intensive numa balancing testing, but it survived
2 weeks with this applied.

# Bug Description

It was reported that a bad pmd is seen when automatic NUMA
balancing is marking page table entries as prot_numa:
    
  [2437548.196018] mm/pgtable-generic.c:50: bad pmd 00000000af22fc02(dffffffe71fbfe02)
  [2437548.235022] Call Trace:
  [2437548.238234]  <TASK>
  [2437548.241060]  dump_stack_lvl+0x46/0x61
  [2437548.245689]  panic+0x106/0x2e5
  [2437548.249497]  pmd_clear_bad+0x3c/0x3c
  [2437548.253967]  change_pmd_range.isra.0+0x34d/0x3a7
  [2437548.259537]  change_p4d_range+0x156/0x20e
  [2437548.264392]  change_protection_range+0x116/0x1a9
  [2437548.269976]  change_prot_numa+0x15/0x37
  [2437548.274774]  task_numa_work+0x1b8/0x302
  [2437548.279512]  task_work_run+0x62/0x95
  [2437548.283882]  exit_to_user_mode_loop+0x1a4/0x1a9
  [2437548.289277]  exit_to_user_mode_prepare+0xf4/0xfc
  [2437548.294751]  ? sysvec_apic_timer_interrupt+0x34/0x81
  [2437548.300677]  irqentry_exit_to_user_mode+0x5/0x25
  [2437548.306153]  asm_sysvec_apic_timer_interrupt+0x16/0x1b

This is due to a race condition between change_prot_numa() and
THP migration because the kernel doesn't check is_swap_pmd() and
pmd_trans_huge() atomically:

change_prot_numa()                      THP migration
======================================================================
- change_pmd_range()
-> is_swap_pmd() returns false,
meaning it's not a PMD migration
entry.
				  - do_huge_pmd_numa_page()
				  -> migrate_misplaced_page() sets
				     migration entries for the THP.
- change_pmd_range()
-> pmd_none_or_clear_bad_unless_trans_huge()
-> pmd_none() and pmd_trans_huge() returns false
- pmd_none_or_clear_bad_unless_trans_huge()
-> pmd_bad() returns true for the migration entry!

The upstream commit 670ddd8cdcbd ("mm/mprotect: delete
pmd_none_or_clear_bad_unless_trans_huge()") closes this race condition
by checking is_swap_pmd() and pmd_trans_huge() atomically.

# Backporting note

commit a79390f5d6a7 ("mm/mprotect: use long for page accountings and retval")
is backported to return an error code (negative value) in
change_pte_range().

Unlike the mainline, pte_offset_map_lock() does not check if the pmd
entry is a migration entry or a hugepage; acquires PTL unconditionally
instead of returning failure. Therefore, it is necessary to keep the
!is_swap_pmd() && !pmd_trans_huge() && !pmd_devmap() checks in
change_pmd_range() before acquiring the PTL.

After acquiring the lock, open-code the semantics of
pte_offset_map_lock() in the mainline kernel; change_pte_range() fails
if the pmd value has changed. This requires adding pmd_old parameter
(pmd_t value that is read before calling the function) to
change_pte_range().

Hugh Dickins (1):
  mm/mprotect: delete pmd_none_or_clear_bad_unless_trans_huge()

Peter Xu (1):
  mm/mprotect: use long for page accountings and retval

 include/linux/hugetlb.h |   4 +-
 include/linux/mm.h      |   2 +-
 mm/hugetlb.c            |   4 +-
 mm/mempolicy.c          |   2 +-
 mm/mprotect.c           | 124 +++++++++++++++++-----------------------
 5 files changed, 60 insertions(+), 76 deletions(-)

-- 
2.43.0

[PATCH V1 5.4.y 1/2] mm/mprotect: use long for page accountings and retval

[Harry Yoo]

From: Peter Xu <peterx@redhat.com>

commit a79390f5d6a78647fd70856bd42b22d994de0ba2 upstream.

Switch to use type "long" for page accountings and retval across the whole
procedure of change_protection().

The change should have shrinked the possible maximum page number to be
half comparing to previous (ULONG_MAX / 2), but it shouldn't overflow on
any system either because the maximum possible pages touched by change
protection should be ULONG_MAX / PAGE_SIZE.

Two reasons to switch from "unsigned long" to "long":

  1. It suites better on count_vm_numa_events(), whose 2nd parameter takes
     a long type.

  2. It paves way for returning negative (error) values in the future.

Currently the only caller that consumes this retval is change_prot_numa(),
where the unsigned long was converted to an int.  Since at it, touching up
the numa code to also take a long, so it'll avoid any possible overflow
too during the int-size convertion.

Link: https://lkml.kernel.org/r/20230104225207.1066932-3-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: James Houghton <jthoughton@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ Adjust context ]
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
---
 include/linux/hugetlb.h |  4 ++--
 include/linux/mm.h      |  2 +-
 mm/hugetlb.c            |  4 ++--
 mm/mempolicy.c          |  2 +-
 mm/mprotect.c           | 26 +++++++++++++-------------
 5 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 311dd8e921826..e94ac3f6d9ba4 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -137,7 +137,7 @@ struct page *follow_huge_pgd(struct mm_struct *mm, unsigned long address,
 
 int pmd_huge(pmd_t pmd);
 int pud_huge(pud_t pud);
-unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
+long hugetlb_change_protection(struct vm_area_struct *vma,
 		unsigned long address, unsigned long end, pgprot_t newprot);
 
 bool is_hugetlb_entry_migration(pte_t pte);
@@ -195,7 +195,7 @@ static inline bool isolate_huge_page(struct page *page, struct list_head *list)
 #define putback_active_hugepage(p)	do {} while (0)
 #define move_hugetlb_state(old, new, reason)	do {} while (0)
 
-static inline unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
+static inline long hugetlb_change_protection(struct vm_area_struct *vma,
 		unsigned long address, unsigned long end, pgprot_t newprot)
 {
 	return 0;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 57cba6e4fdcd7..575b68a47fe55 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1657,7 +1657,7 @@ extern unsigned long move_page_tables(struct vm_area_struct *vma,
 		unsigned long old_addr, struct vm_area_struct *new_vma,
 		unsigned long new_addr, unsigned long len,
 		bool need_rmap_locks);
-extern unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
+extern long change_protection(struct vm_area_struct *vma, unsigned long start,
 			      unsigned long end, pgprot_t newprot,
 			      int dirty_accountable, int prot_numa);
 extern int mprotect_fixup(struct vm_area_struct *vma,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e83563b9ab32b..fe24be944e585 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4635,7 +4635,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 #define flush_hugetlb_tlb_range(vma, addr, end)	flush_tlb_range(vma, addr, end)
 #endif
 
-unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
+long hugetlb_change_protection(struct vm_area_struct *vma,
 		unsigned long address, unsigned long end, pgprot_t newprot)
 {
 	struct mm_struct *mm = vma->vm_mm;
@@ -4643,7 +4643,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
 	pte_t *ptep;
 	pte_t pte;
 	struct hstate *h = hstate_vma(vma);
-	unsigned long pages = 0;
+	long pages = 0;
 	bool shared_pmd = false;
 	struct mmu_notifier_range range;
 
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 2bf4ab7b2713d..576b48984928a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -595,7 +595,7 @@ static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask,
 unsigned long change_prot_numa(struct vm_area_struct *vma,
 			unsigned long addr, unsigned long end)
 {
-	int nr_updated;
+	long nr_updated;
 
 	nr_updated = change_protection(vma, addr, end, PAGE_NONE, 0, 1);
 	if (nr_updated)
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 95dee88f782b6..f222c305cdc7c 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -35,13 +35,13 @@
 
 #include "internal.h"
 
-static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
+static long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 		unsigned long addr, unsigned long end, pgprot_t newprot,
 		int dirty_accountable, int prot_numa)
 {
 	pte_t *pte, oldpte;
 	spinlock_t *ptl;
-	unsigned long pages = 0;
+	long pages = 0;
 	int target_node = NUMA_NO_NODE;
 
 	/*
@@ -186,13 +186,13 @@ static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
 	return 0;
 }
 
-static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
+static inline long change_pmd_range(struct vm_area_struct *vma,
 		pud_t *pud, unsigned long addr, unsigned long end,
 		pgprot_t newprot, int dirty_accountable, int prot_numa)
 {
 	pmd_t *pmd;
 	unsigned long next;
-	unsigned long pages = 0;
+	long pages = 0;
 	unsigned long nr_huge_updates = 0;
 	struct mmu_notifier_range range;
 
@@ -200,7 +200,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 
 	pmd = pmd_offset(pud, addr);
 	do {
-		unsigned long this_pages;
+		long this_pages;
 
 		next = pmd_addr_end(addr, end);
 
@@ -258,13 +258,13 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 	return pages;
 }
 
-static inline unsigned long change_pud_range(struct vm_area_struct *vma,
+static inline long change_pud_range(struct vm_area_struct *vma,
 		p4d_t *p4d, unsigned long addr, unsigned long end,
 		pgprot_t newprot, int dirty_accountable, int prot_numa)
 {
 	pud_t *pud;
 	unsigned long next;
-	unsigned long pages = 0;
+	long pages = 0;
 
 	pud = pud_offset(p4d, addr);
 	do {
@@ -278,13 +278,13 @@ static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 	return pages;
 }
 
-static inline unsigned long change_p4d_range(struct vm_area_struct *vma,
+static inline long change_p4d_range(struct vm_area_struct *vma,
 		pgd_t *pgd, unsigned long addr, unsigned long end,
 		pgprot_t newprot, int dirty_accountable, int prot_numa)
 {
 	p4d_t *p4d;
 	unsigned long next;
-	unsigned long pages = 0;
+	long pages = 0;
 
 	p4d = p4d_offset(pgd, addr);
 	do {
@@ -298,7 +298,7 @@ static inline unsigned long change_p4d_range(struct vm_area_struct *vma,
 	return pages;
 }
 
-static unsigned long change_protection_range(struct vm_area_struct *vma,
+static long change_protection_range(struct vm_area_struct *vma,
 		unsigned long addr, unsigned long end, pgprot_t newprot,
 		int dirty_accountable, int prot_numa)
 {
@@ -306,7 +306,7 @@ static unsigned long change_protection_range(struct vm_area_struct *vma,
 	pgd_t *pgd;
 	unsigned long next;
 	unsigned long start = addr;
-	unsigned long pages = 0;
+	long pages = 0;
 
 	BUG_ON(addr >= end);
 	pgd = pgd_offset(mm, addr);
@@ -328,11 +328,11 @@ static unsigned long change_protection_range(struct vm_area_struct *vma,
 	return pages;
 }
 
-unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
+long change_protection(struct vm_area_struct *vma, unsigned long start,
 		       unsigned long end, pgprot_t newprot,
 		       int dirty_accountable, int prot_numa)
 {
-	unsigned long pages;
+	long pages;
 
 	if (is_vm_hugetlb_page(vma))
 		pages = hugetlb_change_protection(vma, start, end, newprot);
-- 
2.43.0

Patch "mm/mprotect: use long for page accountings and retval" has been added to the 5.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    mm/mprotect: use long for page accountings and retval

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-mprotect-use-long-for-page-accountings-and-retval.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-196860-greg=kroah.com@vger.kernel.org Tue Nov 25 06:10:31 2025
From: Harry Yoo <harry.yoo@oracle.com>
Date: Tue, 25 Nov 2025 14:09:25 +0900
Subject: mm/mprotect: use long for page accountings and retval
To: stable@vger.kernel.org
Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, baohua@kernel.org, baolin.wang@linux.alibaba.com, david@kernel.org, dev.jain@arm.com, hughd@google.com, jane.chu@oracle.com, jannh@google.com, kas@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, npache@redhat.com, pfalcato@suse.de, ryan.roberts@arm.com, vbabka@suse.cz, ziy@nvidia.com, Peter Xu <peterx@redhat.com>, Mike Kravetz <mike.kravetz@oracle.com>, James Houghton <jthoughton@google.com>, Andrea Arcangeli <aarcange@redhat.com>, Axel Rasmussen <axelrasmussen@google.com>, David Hildenbrand <david@redhat.com>, Muchun Song <songmuchun@bytedance.com>, Nadav Amit <nadav.amit@gmail.com>, Harry Yoo <harry.yoo@oracle.com>
Message-ID: <20251125050926.1100484-2-harry.yoo@oracle.com>

From: Peter Xu <peterx@redhat.com>

commit a79390f5d6a78647fd70856bd42b22d994de0ba2 upstream.

Switch to use type "long" for page accountings and retval across the whole
procedure of change_protection().

The change should have shrinked the possible maximum page number to be
half comparing to previous (ULONG_MAX / 2), but it shouldn't overflow on
any system either because the maximum possible pages touched by change
protection should be ULONG_MAX / PAGE_SIZE.

Two reasons to switch from "unsigned long" to "long":

  1. It suites better on count_vm_numa_events(), whose 2nd parameter takes
     a long type.

  2. It paves way for returning negative (error) values in the future.

Currently the only caller that consumes this retval is change_prot_numa(),
where the unsigned long was converted to an int.  Since at it, touching up
the numa code to also take a long, so it'll avoid any possible overflow
too during the int-size convertion.

Link: https://lkml.kernel.org/r/20230104225207.1066932-3-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: James Houghton <jthoughton@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ Adjust context ]
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/hugetlb.h |    4 ++--
 include/linux/mm.h      |    2 +-
 mm/hugetlb.c            |    4 ++--
 mm/mempolicy.c          |    2 +-
 mm/mprotect.c           |   26 +++++++++++++-------------
 5 files changed, 19 insertions(+), 19 deletions(-)

--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -137,7 +137,7 @@ struct page *follow_huge_pgd(struct mm_s
 
 int pmd_huge(pmd_t pmd);
 int pud_huge(pud_t pud);
-unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
+long hugetlb_change_protection(struct vm_area_struct *vma,
 		unsigned long address, unsigned long end, pgprot_t newprot);
 
 bool is_hugetlb_entry_migration(pte_t pte);
@@ -195,7 +195,7 @@ static inline bool isolate_huge_page(str
 #define putback_active_hugepage(p)	do {} while (0)
 #define move_hugetlb_state(old, new, reason)	do {} while (0)
 
-static inline unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
+static inline long hugetlb_change_protection(struct vm_area_struct *vma,
 		unsigned long address, unsigned long end, pgprot_t newprot)
 {
 	return 0;
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1657,7 +1657,7 @@ extern unsigned long move_page_tables(st
 		unsigned long old_addr, struct vm_area_struct *new_vma,
 		unsigned long new_addr, unsigned long len,
 		bool need_rmap_locks);
-extern unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
+extern long change_protection(struct vm_area_struct *vma, unsigned long start,
 			      unsigned long end, pgprot_t newprot,
 			      int dirty_accountable, int prot_numa);
 extern int mprotect_fixup(struct vm_area_struct *vma,
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4635,7 +4635,7 @@ same_page:
 #define flush_hugetlb_tlb_range(vma, addr, end)	flush_tlb_range(vma, addr, end)
 #endif
 
-unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
+long hugetlb_change_protection(struct vm_area_struct *vma,
 		unsigned long address, unsigned long end, pgprot_t newprot)
 {
 	struct mm_struct *mm = vma->vm_mm;
@@ -4643,7 +4643,7 @@ unsigned long hugetlb_change_protection(
 	pte_t *ptep;
 	pte_t pte;
 	struct hstate *h = hstate_vma(vma);
-	unsigned long pages = 0;
+	long pages = 0;
 	bool shared_pmd = false;
 	struct mmu_notifier_range range;
 
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -595,7 +595,7 @@ unlock:
 unsigned long change_prot_numa(struct vm_area_struct *vma,
 			unsigned long addr, unsigned long end)
 {
-	int nr_updated;
+	long nr_updated;
 
 	nr_updated = change_protection(vma, addr, end, PAGE_NONE, 0, 1);
 	if (nr_updated)
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -35,13 +35,13 @@
 
 #include "internal.h"
 
-static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
+static long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 		unsigned long addr, unsigned long end, pgprot_t newprot,
 		int dirty_accountable, int prot_numa)
 {
 	pte_t *pte, oldpte;
 	spinlock_t *ptl;
-	unsigned long pages = 0;
+	long pages = 0;
 	int target_node = NUMA_NO_NODE;
 
 	/*
@@ -186,13 +186,13 @@ static inline int pmd_none_or_clear_bad_
 	return 0;
 }
 
-static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
+static inline long change_pmd_range(struct vm_area_struct *vma,
 		pud_t *pud, unsigned long addr, unsigned long end,
 		pgprot_t newprot, int dirty_accountable, int prot_numa)
 {
 	pmd_t *pmd;
 	unsigned long next;
-	unsigned long pages = 0;
+	long pages = 0;
 	unsigned long nr_huge_updates = 0;
 	struct mmu_notifier_range range;
 
@@ -200,7 +200,7 @@ static inline unsigned long change_pmd_r
 
 	pmd = pmd_offset(pud, addr);
 	do {
-		unsigned long this_pages;
+		long this_pages;
 
 		next = pmd_addr_end(addr, end);
 
@@ -258,13 +258,13 @@ next:
 	return pages;
 }
 
-static inline unsigned long change_pud_range(struct vm_area_struct *vma,
+static inline long change_pud_range(struct vm_area_struct *vma,
 		p4d_t *p4d, unsigned long addr, unsigned long end,
 		pgprot_t newprot, int dirty_accountable, int prot_numa)
 {
 	pud_t *pud;
 	unsigned long next;
-	unsigned long pages = 0;
+	long pages = 0;
 
 	pud = pud_offset(p4d, addr);
 	do {
@@ -278,13 +278,13 @@ static inline unsigned long change_pud_r
 	return pages;
 }
 
-static inline unsigned long change_p4d_range(struct vm_area_struct *vma,
+static inline long change_p4d_range(struct vm_area_struct *vma,
 		pgd_t *pgd, unsigned long addr, unsigned long end,
 		pgprot_t newprot, int dirty_accountable, int prot_numa)
 {
 	p4d_t *p4d;
 	unsigned long next;
-	unsigned long pages = 0;
+	long pages = 0;
 
 	p4d = p4d_offset(pgd, addr);
 	do {
@@ -298,7 +298,7 @@ static inline unsigned long change_p4d_r
 	return pages;
 }
 
-static unsigned long change_protection_range(struct vm_area_struct *vma,
+static long change_protection_range(struct vm_area_struct *vma,
 		unsigned long addr, unsigned long end, pgprot_t newprot,
 		int dirty_accountable, int prot_numa)
 {
@@ -306,7 +306,7 @@ static unsigned long change_protection_r
 	pgd_t *pgd;
 	unsigned long next;
 	unsigned long start = addr;
-	unsigned long pages = 0;
+	long pages = 0;
 
 	BUG_ON(addr >= end);
 	pgd = pgd_offset(mm, addr);
@@ -328,11 +328,11 @@ static unsigned long change_protection_r
 	return pages;
 }
 
-unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
+long change_protection(struct vm_area_struct *vma, unsigned long start,
 		       unsigned long end, pgprot_t newprot,
 		       int dirty_accountable, int prot_numa)
 {
-	unsigned long pages;
+	long pages;
 
 	if (is_vm_hugetlb_page(vma))
 		pages = hugetlb_change_protection(vma, start, end, newprot);


Patches currently in stable-queue which might be from harry.yoo@oracle.com are

queue-5.4/mm-mprotect-delete-pmd_none_or_clear_bad_unless_trans_huge.patch
queue-5.4/mm-mprotect-use-long-for-page-accountings-and-retval.patch

[PATCH V1 5.4.y 2/2] mm/mprotect: delete pmd_none_or_clear_bad_unless_trans_huge()

[Harry Yoo]

From: Hugh Dickins <hughd@google.com>

commit 670ddd8cdcbd1d07a4571266ae3517f821728c3a upstream.

change_pmd_range() had special pmd_none_or_clear_bad_unless_trans_huge(),
required to avoid "bad" choices when setting automatic NUMA hinting under
mmap_read_lock(); but most of that is already covered in pte_offset_map()
now.  change_pmd_range() just wants a pmd_none() check before wasting time
on MMU notifiers, then checks on the read-once _pmd value to work out
what's needed for huge cases.  If change_pte_range() returns -EAGAIN to
retry if pte_offset_map_lock() fails, nothing more special is needed.

Link: https://lkml.kernel.org/r/725a42a9-91e9-c868-925-e3a5fd40bb4f@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ Background:

    It was reported that a bad pmd is seen when automatic NUMA balancing
    is marking page table entries as prot_numa:

      [2437548.196018] mm/pgtable-generic.c:50: bad pmd 00000000af22fc02(dffffffe71fbfe02)
      [2437548.235022] Call Trace:
      [2437548.238234]  <TASK>
      [2437548.241060]  dump_stack_lvl+0x46/0x61
      [2437548.245689]  panic+0x106/0x2e5
      [2437548.249497]  pmd_clear_bad+0x3c/0x3c
      [2437548.253967]  change_pmd_range.isra.0+0x34d/0x3a7
      [2437548.259537]  change_p4d_range+0x156/0x20e
      [2437548.264392]  change_protection_range+0x116/0x1a9
      [2437548.269976]  change_prot_numa+0x15/0x37
      [2437548.274774]  task_numa_work+0x1b8/0x302
      [2437548.279512]  task_work_run+0x62/0x95
      [2437548.283882]  exit_to_user_mode_loop+0x1a4/0x1a9
      [2437548.289277]  exit_to_user_mode_prepare+0xf4/0xfc
      [2437548.294751]  ? sysvec_apic_timer_interrupt+0x34/0x81
      [2437548.300677]  irqentry_exit_to_user_mode+0x5/0x25
      [2437548.306153]  asm_sysvec_apic_timer_interrupt+0x16/0x1b

    This is due to a race condition between change_prot_numa() and
    THP migration because the kernel doesn't check is_swap_pmd() and
    pmd_trans_huge() atomically:

    change_prot_numa()                      THP migration
    ======================================================================
    - change_pmd_range()
    -> is_swap_pmd() returns false,
    meaning it's not a PMD migration
    entry.
                                      - do_huge_pmd_numa_page()
                                      -> migrate_misplaced_page() sets
                                         migration entries for the THP.
    - change_pmd_range()
    -> pmd_none_or_clear_bad_unless_trans_huge()
    -> pmd_none() and pmd_trans_huge() returns false
    - pmd_none_or_clear_bad_unless_trans_huge()
    -> pmd_bad() returns true for the migration entry!

  The upstream commit 670ddd8cdcbd ("mm/mprotect: delete
  pmd_none_or_clear_bad_unless_trans_huge()") closes this race condition
  by checking is_swap_pmd() and pmd_trans_huge() atomically.

  Backporting note:
    Unlike mainline, pte_offset_map_lock() does not check if the pmd
    entry is a migration entry or a hugepage; acquires PTL unconditionally
    instead of returning failure. Therefore, it is necessary to keep the
    !is_swap_pmd() && !pmd_trans_huge() && !pmd_devmap() check before
    acquiring the PTL.

    After acquiring it, open-code the mainline semantics of
    pte_offset_map_lock() so that change_pte_range() fails if the pmd value
    has changed (under the PTL). This requires adding one more parameter
    (for passing pmd value that is read before calling the function) to
    change_pte_range(). ]
---
 mm/mprotect.c | 100 +++++++++++++++++++++-----------------------------
 1 file changed, 42 insertions(+), 58 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index f222c305cdc7c..3b2f956cc0619 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -36,29 +36,24 @@
 #include "internal.h"
 
 static long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
-		unsigned long addr, unsigned long end, pgprot_t newprot,
-		int dirty_accountable, int prot_numa)
+		pmd_t pmd_old, unsigned long addr, unsigned long end,
+		pgprot_t newprot, int dirty_accountable, int prot_numa)
 {
 	pte_t *pte, oldpte;
+	pmd_t pmd_val;
 	spinlock_t *ptl;
 	long pages = 0;
 	int target_node = NUMA_NO_NODE;
 
-	/*
-	 * Can be called with only the mmap_sem for reading by
-	 * prot_numa so we must check the pmd isn't constantly
-	 * changing from under us from pmd_none to pmd_trans_huge
-	 * and/or the other way around.
-	 */
-	if (pmd_trans_unstable(pmd))
-		return 0;
-
-	/*
-	 * The pmd points to a regular pte so the pmd can't change
-	 * from under us even if the mmap_sem is only hold for
-	 * reading.
-	 */
 	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+	/* Make sure pmd didn't change after acquiring ptl */
+	pmd_val = pmd_read_atomic(pmd);
+	/* See pmd_none_or_trans_huge_or_clear_bad for info on barrier */
+	barrier();
+	if (!pmd_same(pmd_old, pmd_val)) {
+		pte_unmap_unlock(pte, ptl);
+		return -EAGAIN;
+	}
 
 	/* Get target node for single threaded private VMAs */
 	if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
@@ -161,31 +156,6 @@ static long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 	return pages;
 }
 
-/*
- * Used when setting automatic NUMA hinting protection where it is
- * critical that a numa hinting PMD is not confused with a bad PMD.
- */
-static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
-{
-	pmd_t pmdval = pmd_read_atomic(pmd);
-
-	/* See pmd_none_or_trans_huge_or_clear_bad for info on barrier */
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	barrier();
-#endif
-
-	if (pmd_none(pmdval))
-		return 1;
-	if (pmd_trans_huge(pmdval))
-		return 0;
-	if (unlikely(pmd_bad(pmdval))) {
-		pmd_clear_bad(pmd);
-		return 1;
-	}
-
-	return 0;
-}
-
 static inline long change_pmd_range(struct vm_area_struct *vma,
 		pud_t *pud, unsigned long addr, unsigned long end,
 		pgprot_t newprot, int dirty_accountable, int prot_numa)
@@ -200,21 +170,33 @@ static inline long change_pmd_range(struct vm_area_struct *vma,
 
 	pmd = pmd_offset(pud, addr);
 	do {
-		long this_pages;
-
+		long ret;
+		pmd_t _pmd;
+again:
 		next = pmd_addr_end(addr, end);
+		_pmd = pmd_read_atomic(pmd);
+		/* See pmd_none_or_trans_huge_or_clear_bad for info on barrier */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+		barrier();
+#endif
 
 		/*
 		 * Automatic NUMA balancing walks the tables with mmap_sem
 		 * held for read. It's possible a parallel update to occur
-		 * between pmd_trans_huge() and a pmd_none_or_clear_bad()
-		 * check leading to a false positive and clearing.
-		 * Hence, it's necessary to atomically read the PMD value
-		 * for all the checks.
+		 * between pmd_trans_huge(), is_swap_pmd(), and
+		 * a pmd_none_or_clear_bad() check leading to a false positive
+		 * and clearing. Hence, it's necessary to atomically read
+		 * the PMD value for all the checks.
 		 */
-		if (!is_swap_pmd(*pmd) && !pmd_devmap(*pmd) &&
-		     pmd_none_or_clear_bad_unless_trans_huge(pmd))
-			goto next;
+		if (!is_swap_pmd(_pmd) && !pmd_devmap(_pmd) && !pmd_trans_huge(_pmd)) {
+			if (pmd_none(_pmd))
+				goto next;
+
+			if (pmd_bad(_pmd)) {
+				pmd_clear_bad(pmd);
+				goto next;
+			}
+		}
 
 		/* invoke the mmu notifier if the pmd is populated */
 		if (!range.start) {
@@ -224,15 +206,15 @@ static inline long change_pmd_range(struct vm_area_struct *vma,
 			mmu_notifier_invalidate_range_start(&range);
 		}
 
-		if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
+		if (is_swap_pmd(_pmd) || pmd_trans_huge(_pmd) || pmd_devmap(_pmd)) {
 			if (next - addr != HPAGE_PMD_SIZE) {
 				__split_huge_pmd(vma, pmd, addr, false, NULL);
 			} else {
-				int nr_ptes = change_huge_pmd(vma, pmd, addr,
-						newprot, prot_numa);
+				ret = change_huge_pmd(vma, pmd, addr, newprot,
+						      prot_numa);
 
-				if (nr_ptes) {
-					if (nr_ptes == HPAGE_PMD_NR) {
+				if (ret) {
+					if (ret == HPAGE_PMD_NR) {
 						pages += HPAGE_PMD_NR;
 						nr_huge_updates++;
 					}
@@ -243,9 +225,11 @@ static inline long change_pmd_range(struct vm_area_struct *vma,
 			}
 			/* fall through, the trans huge pmd just split */
 		}
-		this_pages = change_pte_range(vma, pmd, addr, next, newprot,
-				 dirty_accountable, prot_numa);
-		pages += this_pages;
+		ret = change_pte_range(vma, pmd, _pmd, addr, next,
+				       newprot, dirty_accountable, prot_numa);
+		if (ret < 0)
+			goto again;
+		pages += ret;
 next:
 		cond_resched();
 	} while (pmd++, addr = next, addr != end);
-- 
2.43.0

Patch "mm/mprotect: delete pmd_none_or_clear_bad_unless_trans_huge()" has been added to the 5.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    mm/mprotect: delete pmd_none_or_clear_bad_unless_trans_huge()

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-mprotect-delete-pmd_none_or_clear_bad_unless_trans_huge.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-196861-greg=kroah.com@vger.kernel.org Tue Nov 25 06:10:55 2025
From: Harry Yoo <harry.yoo@oracle.com>
Date: Tue, 25 Nov 2025 14:09:26 +0900
Subject: mm/mprotect: delete pmd_none_or_clear_bad_unless_trans_huge()
To: stable@vger.kernel.org
Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, baohua@kernel.org, baolin.wang@linux.alibaba.com, david@kernel.org, dev.jain@arm.com, hughd@google.com, jane.chu@oracle.com, jannh@google.com, kas@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, npache@redhat.com, pfalcato@suse.de, ryan.roberts@arm.com, vbabka@suse.cz, ziy@nvidia.com, "Alistair Popple" <apopple@nvidia.com>, "Anshuman Khandual" <anshuman.khandual@arm.com>, "Axel Rasmussen" <axelrasmussen@google.com>, "Christophe Leroy" <christophe.leroy@csgroup.eu>, "Christoph Hellwig" <hch@infradead.org>, "David Hildenbrand" <david@redhat.com>, "Huang, Ying" <ying.huang@intel.com>, "Ira Weiny" <ira.weiny@intel.com>, "Jason Gunthorpe" <jgg@ziepe.ca>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, "Lorenzo Stoakes" <lstoakes@gmail.com>, "Matthew Wilcox" <willy@infradead.org>, "Mel Gorman" <mgorman@techsingularity.net>, "Miaohe Lin" <linmiaohe@huawei.com>, "Mike Kravetz" <mike.kra
 vetz@ora
 cle.com>, "Mike Rapoport" <rppt@kernel.org>, "Minchan Kim" <minchan@kernel.org>, "Naoya Horiguchi" <naoya.horiguchi@nec.com>, "Pavel Tatashin" <pasha.tatashin@soleen.com>, "Peter Xu" <peterx@redhat.com>, "Peter Zijlstra" <peterz@infradead.org>, "Qi Zheng" <zhengqi.arch@bytedance.com>, "Ralph Campbell" <rcampbell@nvidia.com>, "SeongJae Park" <sj@kernel.org>, "Song Liu" <song@kernel.org>, "Steven Price" <steven.price@arm.com>, "Suren Baghdasaryan" <surenb@google.com>, "Thomas Hellström" <thomas.hellstrom@linux.intel.com>, "Will Deacon" <will@kernel.org>, "Yang Shi" <shy828301@gmail.com>, "Yu Zhao" <yuzhao@google.com>, "Zack Rusin" <zackr@vmware.com>
Message-ID: <20251125050926.1100484-3-harry.yoo@oracle.com>

From: Hugh Dickins <hughd@google.com>

commit 670ddd8cdcbd1d07a4571266ae3517f821728c3a upstream.

change_pmd_range() had special pmd_none_or_clear_bad_unless_trans_huge(),
required to avoid "bad" choices when setting automatic NUMA hinting under
mmap_read_lock(); but most of that is already covered in pte_offset_map()
now.  change_pmd_range() just wants a pmd_none() check before wasting time
on MMU notifiers, then checks on the read-once _pmd value to work out
what's needed for huge cases.  If change_pte_range() returns -EAGAIN to
retry if pte_offset_map_lock() fails, nothing more special is needed.

Link: https://lkml.kernel.org/r/725a42a9-91e9-c868-925-e3a5fd40bb4f@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ Background:

    It was reported that a bad pmd is seen when automatic NUMA balancing
    is marking page table entries as prot_numa:

      [2437548.196018] mm/pgtable-generic.c:50: bad pmd 00000000af22fc02(dffffffe71fbfe02)
      [2437548.235022] Call Trace:
      [2437548.238234]  <TASK>
      [2437548.241060]  dump_stack_lvl+0x46/0x61
      [2437548.245689]  panic+0x106/0x2e5
      [2437548.249497]  pmd_clear_bad+0x3c/0x3c
      [2437548.253967]  change_pmd_range.isra.0+0x34d/0x3a7
      [2437548.259537]  change_p4d_range+0x156/0x20e
      [2437548.264392]  change_protection_range+0x116/0x1a9
      [2437548.269976]  change_prot_numa+0x15/0x37
      [2437548.274774]  task_numa_work+0x1b8/0x302
      [2437548.279512]  task_work_run+0x62/0x95
      [2437548.283882]  exit_to_user_mode_loop+0x1a4/0x1a9
      [2437548.289277]  exit_to_user_mode_prepare+0xf4/0xfc
      [2437548.294751]  ? sysvec_apic_timer_interrupt+0x34/0x81
      [2437548.300677]  irqentry_exit_to_user_mode+0x5/0x25
      [2437548.306153]  asm_sysvec_apic_timer_interrupt+0x16/0x1b

    This is due to a race condition between change_prot_numa() and
    THP migration because the kernel doesn't check is_swap_pmd() and
    pmd_trans_huge() atomically:

    change_prot_numa()                      THP migration
    ======================================================================
    - change_pmd_range()
    -> is_swap_pmd() returns false,
    meaning it's not a PMD migration
    entry.
                                      - do_huge_pmd_numa_page()
                                      -> migrate_misplaced_page() sets
                                         migration entries for the THP.
    - change_pmd_range()
    -> pmd_none_or_clear_bad_unless_trans_huge()
    -> pmd_none() and pmd_trans_huge() returns false
    - pmd_none_or_clear_bad_unless_trans_huge()
    -> pmd_bad() returns true for the migration entry!

  The upstream commit 670ddd8cdcbd ("mm/mprotect: delete
  pmd_none_or_clear_bad_unless_trans_huge()") closes this race condition
  by checking is_swap_pmd() and pmd_trans_huge() atomically.

  Backporting note:
    Unlike mainline, pte_offset_map_lock() does not check if the pmd
    entry is a migration entry or a hugepage; acquires PTL unconditionally
    instead of returning failure. Therefore, it is necessary to keep the
    !is_swap_pmd() && !pmd_trans_huge() && !pmd_devmap() check before
    acquiring the PTL.

    After acquiring it, open-code the mainline semantics of
    pte_offset_map_lock() so that change_pte_range() fails if the pmd value
    has changed (under the PTL). This requires adding one more parameter
    (for passing pmd value that is read before calling the function) to
    change_pte_range(). ]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/mprotect.c |  100 ++++++++++++++++++++++++----------------------------------
 1 file changed, 42 insertions(+), 58 deletions(-)

--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -36,29 +36,24 @@
 #include "internal.h"
 
 static long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
-		unsigned long addr, unsigned long end, pgprot_t newprot,
-		int dirty_accountable, int prot_numa)
+		pmd_t pmd_old, unsigned long addr, unsigned long end,
+		pgprot_t newprot, int dirty_accountable, int prot_numa)
 {
 	pte_t *pte, oldpte;
+	pmd_t pmd_val;
 	spinlock_t *ptl;
 	long pages = 0;
 	int target_node = NUMA_NO_NODE;
 
-	/*
-	 * Can be called with only the mmap_sem for reading by
-	 * prot_numa so we must check the pmd isn't constantly
-	 * changing from under us from pmd_none to pmd_trans_huge
-	 * and/or the other way around.
-	 */
-	if (pmd_trans_unstable(pmd))
-		return 0;
-
-	/*
-	 * The pmd points to a regular pte so the pmd can't change
-	 * from under us even if the mmap_sem is only hold for
-	 * reading.
-	 */
 	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+	/* Make sure pmd didn't change after acquiring ptl */
+	pmd_val = pmd_read_atomic(pmd);
+	/* See pmd_none_or_trans_huge_or_clear_bad for info on barrier */
+	barrier();
+	if (!pmd_same(pmd_old, pmd_val)) {
+		pte_unmap_unlock(pte, ptl);
+		return -EAGAIN;
+	}
 
 	/* Get target node for single threaded private VMAs */
 	if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
@@ -161,31 +156,6 @@ static long change_pte_range(struct vm_a
 	return pages;
 }
 
-/*
- * Used when setting automatic NUMA hinting protection where it is
- * critical that a numa hinting PMD is not confused with a bad PMD.
- */
-static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
-{
-	pmd_t pmdval = pmd_read_atomic(pmd);
-
-	/* See pmd_none_or_trans_huge_or_clear_bad for info on barrier */
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	barrier();
-#endif
-
-	if (pmd_none(pmdval))
-		return 1;
-	if (pmd_trans_huge(pmdval))
-		return 0;
-	if (unlikely(pmd_bad(pmdval))) {
-		pmd_clear_bad(pmd);
-		return 1;
-	}
-
-	return 0;
-}
-
 static inline long change_pmd_range(struct vm_area_struct *vma,
 		pud_t *pud, unsigned long addr, unsigned long end,
 		pgprot_t newprot, int dirty_accountable, int prot_numa)
@@ -200,21 +170,33 @@ static inline long change_pmd_range(stru
 
 	pmd = pmd_offset(pud, addr);
 	do {
-		long this_pages;
-
+		long ret;
+		pmd_t _pmd;
+again:
 		next = pmd_addr_end(addr, end);
+		_pmd = pmd_read_atomic(pmd);
+		/* See pmd_none_or_trans_huge_or_clear_bad for info on barrier */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+		barrier();
+#endif
 
 		/*
 		 * Automatic NUMA balancing walks the tables with mmap_sem
 		 * held for read. It's possible a parallel update to occur
-		 * between pmd_trans_huge() and a pmd_none_or_clear_bad()
-		 * check leading to a false positive and clearing.
-		 * Hence, it's necessary to atomically read the PMD value
-		 * for all the checks.
+		 * between pmd_trans_huge(), is_swap_pmd(), and
+		 * a pmd_none_or_clear_bad() check leading to a false positive
+		 * and clearing. Hence, it's necessary to atomically read
+		 * the PMD value for all the checks.
 		 */
-		if (!is_swap_pmd(*pmd) && !pmd_devmap(*pmd) &&
-		     pmd_none_or_clear_bad_unless_trans_huge(pmd))
-			goto next;
+		if (!is_swap_pmd(_pmd) && !pmd_devmap(_pmd) && !pmd_trans_huge(_pmd)) {
+			if (pmd_none(_pmd))
+				goto next;
+
+			if (pmd_bad(_pmd)) {
+				pmd_clear_bad(pmd);
+				goto next;
+			}
+		}
 
 		/* invoke the mmu notifier if the pmd is populated */
 		if (!range.start) {
@@ -224,15 +206,15 @@ static inline long change_pmd_range(stru
 			mmu_notifier_invalidate_range_start(&range);
 		}
 
-		if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
+		if (is_swap_pmd(_pmd) || pmd_trans_huge(_pmd) || pmd_devmap(_pmd)) {
 			if (next - addr != HPAGE_PMD_SIZE) {
 				__split_huge_pmd(vma, pmd, addr, false, NULL);
 			} else {
-				int nr_ptes = change_huge_pmd(vma, pmd, addr,
-						newprot, prot_numa);
+				ret = change_huge_pmd(vma, pmd, addr, newprot,
+						      prot_numa);
 
-				if (nr_ptes) {
-					if (nr_ptes == HPAGE_PMD_NR) {
+				if (ret) {
+					if (ret == HPAGE_PMD_NR) {
 						pages += HPAGE_PMD_NR;
 						nr_huge_updates++;
 					}
@@ -243,9 +225,11 @@ static inline long change_pmd_range(stru
 			}
 			/* fall through, the trans huge pmd just split */
 		}
-		this_pages = change_pte_range(vma, pmd, addr, next, newprot,
-				 dirty_accountable, prot_numa);
-		pages += this_pages;
+		ret = change_pte_range(vma, pmd, _pmd, addr, next,
+				       newprot, dirty_accountable, prot_numa);
+		if (ret < 0)
+			goto again;
+		pages += ret;
 next:
 		cond_resched();
 	} while (pmd++, addr = next, addr != end);


Patches currently in stable-queue which might be from harry.yoo@oracle.com are

queue-5.4/mm-mprotect-delete-pmd_none_or_clear_bad_unless_trans_huge.patch
queue-5.4/mm-mprotect-use-long-for-page-accountings-and-retval.patch