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* [RFC PATCH 1/2] mm/mremap: Fix race between MOVE_PMD mremap and pageout
@ 2021-05-25  8:33 ` Aneesh Kumar K.V
  0 siblings, 0 replies; 6+ messages in thread
From: Aneesh Kumar K.V @ 2021-05-25  8:33 UTC (permalink / raw)
  To: linux-mm, akpm
  Cc: mpe, linuxppc-dev, kaleshsingh, npiggin, joel, Christophe Leroy,
	Linus Torvalds, Kirill A . Shutemov, Aneesh Kumar K.V

CPU 1				CPU 2					CPU 3

mremap(old_addr, new_addr)      page_shrinker/try_to_unmap_one

mmap_write_lock_killable()

				addr = old_addr
				lock(pte_ptl)
lock(pmd_ptl)
pmd = *old_pmd
pmd_clear(old_pmd)
flush_tlb_range(old_addr)

*new_pmd = pmd
									*new_addr = 10; and fills
									TLB with new addr
									and old pfn

unlock(pmd_ptl)
				ptep_clear_flush()
				old pfn is free.
									Stale TLB entry

Fix this race by holding pmd lock in pageout. This still doesn't handle the race
between MOVE_PUD and pageout.

Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
Link: https://lore.kernel.org/linux-mm/CAHk-=wgXVR04eBNtxQfevontWnP6FDm+oj5vauQXP3S-huwbPw@mail.gmail.com
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/rmap.h |  9 ++++++---
 mm/page_vma_mapped.c | 36 ++++++++++++++++++------------------
 2 files changed, 24 insertions(+), 21 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index def5c62c93b3..272ab0c2b60b 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -207,7 +207,8 @@ struct page_vma_mapped_walk {
 	unsigned long address;
 	pmd_t *pmd;
 	pte_t *pte;
-	spinlock_t *ptl;
+	spinlock_t *pte_ptl;
+	spinlock_t *pmd_ptl;
 	unsigned int flags;
 };
 
@@ -216,8 +217,10 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
 	/* HugeTLB pte is set to the relevant page table entry without pte_mapped. */
 	if (pvmw->pte && !PageHuge(pvmw->page))
 		pte_unmap(pvmw->pte);
-	if (pvmw->ptl)
-		spin_unlock(pvmw->ptl);
+	if (pvmw->pte_ptl)
+		spin_unlock(pvmw->pte_ptl);
+	if (pvmw->pmd_ptl)
+		spin_unlock(pvmw->pmd_ptl);
 }
 
 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 2cf01d933f13..87a2c94c7e27 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -47,8 +47,10 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw)
 				return false;
 		}
 	}
-	pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
-	spin_lock(pvmw->ptl);
+	if (USE_SPLIT_PTE_PTLOCKS) {
+		pvmw->pte_ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
+		spin_lock(pvmw->pte_ptl);
+	}
 	return true;
 }
 
@@ -162,8 +164,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 		if (!pvmw->pte)
 			return false;
 
-		pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
-		spin_lock(pvmw->ptl);
+		pvmw->pte_ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
+		spin_lock(pvmw->pte_ptl);
 		if (!check_pte(pvmw))
 			return not_found(pvmw);
 		return true;
@@ -179,6 +181,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 	if (!pud_present(*pud))
 		return false;
 	pvmw->pmd = pmd_offset(pud, pvmw->address);
+	pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd);
 	/*
 	 * Make sure the pmd value isn't cached in a register by the
 	 * compiler and used as a stale value after we've observed a
@@ -186,7 +189,6 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 	 */
 	pmde = READ_ONCE(*pvmw->pmd);
 	if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
-		pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 		if (likely(pmd_trans_huge(*pvmw->pmd))) {
 			if (pvmw->flags & PVMW_MIGRATION)
 				return not_found(pvmw);
@@ -206,14 +208,10 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 				}
 			}
 			return not_found(pvmw);
-		} else {
-			/* THP pmd was split under us: handle on pte level */
-			spin_unlock(pvmw->ptl);
-			pvmw->ptl = NULL;
 		}
-	} else if (!pmd_present(pmde)) {
-		return false;
-	}
+	} else if (!pmd_present(pmde))
+		return not_found(pvmw);
+
 	if (!map_pte(pvmw))
 		goto next_pte;
 	while (1) {
@@ -233,19 +231,21 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 			/* Did we cross page table boundary? */
 			if (pvmw->address % PMD_SIZE == 0) {
 				pte_unmap(pvmw->pte);
-				if (pvmw->ptl) {
-					spin_unlock(pvmw->ptl);
-					pvmw->ptl = NULL;
+				if (pvmw->pte_ptl) {
+					spin_unlock(pvmw->pte_ptl);
+					pvmw->pte_ptl = NULL;
 				}
+				spin_unlock(pvmw->pmd_ptl);
+				pvmw->pmd_ptl = NULL;
 				goto restart;
 			} else {
 				pvmw->pte++;
 			}
 		} while (pte_none(*pvmw->pte));
 
-		if (!pvmw->ptl) {
-			pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
-			spin_lock(pvmw->ptl);
+		if (USE_SPLIT_PTE_PTLOCKS && !pvmw->pte_ptl) {
+			pvmw->pte_ptl = pte_lockptr(mm, pvmw->pmd);
+			spin_lock(pvmw->pte_ptl);
 		}
 	}
 }
-- 
2.31.1



^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [RFC PATCH 1/2] mm/mremap: Fix race between MOVE_PMD mremap and pageout
@ 2021-05-25  8:33 ` Aneesh Kumar K.V
  0 siblings, 0 replies; 6+ messages in thread
From: Aneesh Kumar K.V @ 2021-05-25  8:33 UTC (permalink / raw)
  To: linux-mm, akpm
  Cc: Aneesh Kumar K.V, Linus Torvalds, npiggin, kaleshsingh, joel,
	Kirill A . Shutemov, linuxppc-dev

CPU 1				CPU 2					CPU 3

mremap(old_addr, new_addr)      page_shrinker/try_to_unmap_one

mmap_write_lock_killable()

				addr = old_addr
				lock(pte_ptl)
lock(pmd_ptl)
pmd = *old_pmd
pmd_clear(old_pmd)
flush_tlb_range(old_addr)

*new_pmd = pmd
									*new_addr = 10; and fills
									TLB with new addr
									and old pfn

unlock(pmd_ptl)
				ptep_clear_flush()
				old pfn is free.
									Stale TLB entry

Fix this race by holding pmd lock in pageout. This still doesn't handle the race
between MOVE_PUD and pageout.

Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
Link: https://lore.kernel.org/linux-mm/CAHk-=wgXVR04eBNtxQfevontWnP6FDm+oj5vauQXP3S-huwbPw@mail.gmail.com
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/rmap.h |  9 ++++++---
 mm/page_vma_mapped.c | 36 ++++++++++++++++++------------------
 2 files changed, 24 insertions(+), 21 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index def5c62c93b3..272ab0c2b60b 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -207,7 +207,8 @@ struct page_vma_mapped_walk {
 	unsigned long address;
 	pmd_t *pmd;
 	pte_t *pte;
-	spinlock_t *ptl;
+	spinlock_t *pte_ptl;
+	spinlock_t *pmd_ptl;
 	unsigned int flags;
 };
 
@@ -216,8 +217,10 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
 	/* HugeTLB pte is set to the relevant page table entry without pte_mapped. */
 	if (pvmw->pte && !PageHuge(pvmw->page))
 		pte_unmap(pvmw->pte);
-	if (pvmw->ptl)
-		spin_unlock(pvmw->ptl);
+	if (pvmw->pte_ptl)
+		spin_unlock(pvmw->pte_ptl);
+	if (pvmw->pmd_ptl)
+		spin_unlock(pvmw->pmd_ptl);
 }
 
 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 2cf01d933f13..87a2c94c7e27 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -47,8 +47,10 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw)
 				return false;
 		}
 	}
-	pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
-	spin_lock(pvmw->ptl);
+	if (USE_SPLIT_PTE_PTLOCKS) {
+		pvmw->pte_ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
+		spin_lock(pvmw->pte_ptl);
+	}
 	return true;
 }
 
@@ -162,8 +164,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 		if (!pvmw->pte)
 			return false;
 
-		pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
-		spin_lock(pvmw->ptl);
+		pvmw->pte_ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
+		spin_lock(pvmw->pte_ptl);
 		if (!check_pte(pvmw))
 			return not_found(pvmw);
 		return true;
@@ -179,6 +181,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 	if (!pud_present(*pud))
 		return false;
 	pvmw->pmd = pmd_offset(pud, pvmw->address);
+	pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd);
 	/*
 	 * Make sure the pmd value isn't cached in a register by the
 	 * compiler and used as a stale value after we've observed a
@@ -186,7 +189,6 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 	 */
 	pmde = READ_ONCE(*pvmw->pmd);
 	if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
-		pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 		if (likely(pmd_trans_huge(*pvmw->pmd))) {
 			if (pvmw->flags & PVMW_MIGRATION)
 				return not_found(pvmw);
@@ -206,14 +208,10 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 				}
 			}
 			return not_found(pvmw);
-		} else {
-			/* THP pmd was split under us: handle on pte level */
-			spin_unlock(pvmw->ptl);
-			pvmw->ptl = NULL;
 		}
-	} else if (!pmd_present(pmde)) {
-		return false;
-	}
+	} else if (!pmd_present(pmde))
+		return not_found(pvmw);
+
 	if (!map_pte(pvmw))
 		goto next_pte;
 	while (1) {
@@ -233,19 +231,21 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 			/* Did we cross page table boundary? */
 			if (pvmw->address % PMD_SIZE == 0) {
 				pte_unmap(pvmw->pte);
-				if (pvmw->ptl) {
-					spin_unlock(pvmw->ptl);
-					pvmw->ptl = NULL;
+				if (pvmw->pte_ptl) {
+					spin_unlock(pvmw->pte_ptl);
+					pvmw->pte_ptl = NULL;
 				}
+				spin_unlock(pvmw->pmd_ptl);
+				pvmw->pmd_ptl = NULL;
 				goto restart;
 			} else {
 				pvmw->pte++;
 			}
 		} while (pte_none(*pvmw->pte));
 
-		if (!pvmw->ptl) {
-			pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
-			spin_lock(pvmw->ptl);
+		if (USE_SPLIT_PTE_PTLOCKS && !pvmw->pte_ptl) {
+			pvmw->pte_ptl = pte_lockptr(mm, pvmw->pmd);
+			spin_lock(pvmw->pte_ptl);
 		}
 	}
 }
-- 
2.31.1


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [RFC PATCH 2/2] mm/mremap: Fix race between MOVE_PUD mremap and pageout
  2021-05-25  8:33 ` Aneesh Kumar K.V
@ 2021-05-25  8:33   ` Aneesh Kumar K.V
  -1 siblings, 0 replies; 6+ messages in thread
From: Aneesh Kumar K.V @ 2021-05-25  8:33 UTC (permalink / raw)
  To: linux-mm, akpm
  Cc: mpe, linuxppc-dev, kaleshsingh, npiggin, joel, Christophe Leroy,
	Linus Torvalds, Kirill A . Shutemov, Aneesh Kumar K.V

CPU 1				CPU 2					CPU 3

mremap(old_addr, new_addr)      page_shrinker/try_to_unmap_one

mmap_write_lock_killable()

				addr = old_addr
				lock(pte_ptl)
lock(pud_ptl)
pud = *old_pud
pud_clear(old_pud)
flush_tlb_range(old_addr)

*new_pud = pud
									*new_addr = 10; and fills
									TLB with new addr
									and old pfn

unlock(pud_ptl)
				ptep_clear_flush()
				old pfn is free.
									Stale TLB entry

Fix this race by holding pud lock in pageout.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/rmap.h |  4 ++++
 mm/page_vma_mapped.c | 13 ++++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 272ab0c2b60b..491c65ce1d46 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -209,6 +209,7 @@ struct page_vma_mapped_walk {
 	pte_t *pte;
 	spinlock_t *pte_ptl;
 	spinlock_t *pmd_ptl;
+	spinlock_t *pud_ptl;
 	unsigned int flags;
 };
 
@@ -221,6 +222,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
 		spin_unlock(pvmw->pte_ptl);
 	if (pvmw->pmd_ptl)
 		spin_unlock(pvmw->pmd_ptl);
+	if (pvmw->pud_ptl)
+		spin_unlock(pvmw->pud_ptl);
+
 }
 
 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 87a2c94c7e27..c913bc34b1d3 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -180,8 +180,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 	pud = pud_offset(p4d, pvmw->address);
 	if (!pud_present(*pud))
 		return false;
+
+	pvmw->pud_ptl = pud_lock(mm, pud);
 	pvmw->pmd = pmd_offset(pud, pvmw->address);
-	pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd);
+	if (USE_SPLIT_PMD_PTLOCKS)
+		pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd);
 	/*
 	 * Make sure the pmd value isn't cached in a register by the
 	 * compiler and used as a stale value after we've observed a
@@ -235,8 +238,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 					spin_unlock(pvmw->pte_ptl);
 					pvmw->pte_ptl = NULL;
 				}
-				spin_unlock(pvmw->pmd_ptl);
-				pvmw->pmd_ptl = NULL;
+				if (pvmw->pmd_ptl) {
+					spin_unlock(pvmw->pmd_ptl);
+					pvmw->pmd_ptl = NULL;
+				}
+				spin_unlock(pvmw->pud_ptl);
+				pvmw->pud_ptl = NULL;
 				goto restart;
 			} else {
 				pvmw->pte++;
-- 
2.31.1



^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [RFC PATCH 2/2] mm/mremap: Fix race between MOVE_PUD mremap and pageout
@ 2021-05-25  8:33   ` Aneesh Kumar K.V
  0 siblings, 0 replies; 6+ messages in thread
From: Aneesh Kumar K.V @ 2021-05-25  8:33 UTC (permalink / raw)
  To: linux-mm, akpm
  Cc: Aneesh Kumar K.V, Linus Torvalds, npiggin, kaleshsingh, joel,
	Kirill A . Shutemov, linuxppc-dev

CPU 1				CPU 2					CPU 3

mremap(old_addr, new_addr)      page_shrinker/try_to_unmap_one

mmap_write_lock_killable()

				addr = old_addr
				lock(pte_ptl)
lock(pud_ptl)
pud = *old_pud
pud_clear(old_pud)
flush_tlb_range(old_addr)

*new_pud = pud
									*new_addr = 10; and fills
									TLB with new addr
									and old pfn

unlock(pud_ptl)
				ptep_clear_flush()
				old pfn is free.
									Stale TLB entry

Fix this race by holding pud lock in pageout.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/rmap.h |  4 ++++
 mm/page_vma_mapped.c | 13 ++++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 272ab0c2b60b..491c65ce1d46 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -209,6 +209,7 @@ struct page_vma_mapped_walk {
 	pte_t *pte;
 	spinlock_t *pte_ptl;
 	spinlock_t *pmd_ptl;
+	spinlock_t *pud_ptl;
 	unsigned int flags;
 };
 
@@ -221,6 +222,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
 		spin_unlock(pvmw->pte_ptl);
 	if (pvmw->pmd_ptl)
 		spin_unlock(pvmw->pmd_ptl);
+	if (pvmw->pud_ptl)
+		spin_unlock(pvmw->pud_ptl);
+
 }
 
 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 87a2c94c7e27..c913bc34b1d3 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -180,8 +180,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 	pud = pud_offset(p4d, pvmw->address);
 	if (!pud_present(*pud))
 		return false;
+
+	pvmw->pud_ptl = pud_lock(mm, pud);
 	pvmw->pmd = pmd_offset(pud, pvmw->address);
-	pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd);
+	if (USE_SPLIT_PMD_PTLOCKS)
+		pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd);
 	/*
 	 * Make sure the pmd value isn't cached in a register by the
 	 * compiler and used as a stale value after we've observed a
@@ -235,8 +238,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 					spin_unlock(pvmw->pte_ptl);
 					pvmw->pte_ptl = NULL;
 				}
-				spin_unlock(pvmw->pmd_ptl);
-				pvmw->pmd_ptl = NULL;
+				if (pvmw->pmd_ptl) {
+					spin_unlock(pvmw->pmd_ptl);
+					pvmw->pmd_ptl = NULL;
+				}
+				spin_unlock(pvmw->pud_ptl);
+				pvmw->pud_ptl = NULL;
 				goto restart;
 			} else {
 				pvmw->pte++;
-- 
2.31.1


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [RFC PATCH 2/2] mm/mremap: Fix race between MOVE_PUD mremap and pageout
  2021-05-25  8:33   ` Aneesh Kumar K.V
@ 2021-05-25 17:28     ` Linus Torvalds
  -1 siblings, 0 replies; 6+ messages in thread
From: Linus Torvalds @ 2021-05-25 17:28 UTC (permalink / raw)
  To: Aneesh Kumar K.V
  Cc: Linux-MM, Andrew Morton, Michael Ellerman, linuxppc-dev,
	Kalesh Singh, Nick Piggin, Joel Fernandes, Christophe Leroy,
	Kirill A . Shutemov

On Mon, May 24, 2021 at 10:34 PM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> @@ -221,6 +222,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
>                 spin_unlock(pvmw->pte_ptl);
>         if (pvmw->pmd_ptl)
>                 spin_unlock(pvmw->pmd_ptl);
> +       if (pvmw->pud_ptl)
> +               spin_unlock(pvmw->pud_ptl);
> +
>  }

You have this habit of adding odd whitespace..

But yes, this seems to be the right way to fix the races properly. The
pageout code is special, the pageout code is normally not critical, so
it's the pageout code that should go the extra mile to make up for the
fact that it doesn't hold the mmap_sem like good page table
modification codepaths do.

                Linus


^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [RFC PATCH 2/2] mm/mremap: Fix race between MOVE_PUD mremap and pageout
@ 2021-05-25 17:28     ` Linus Torvalds
  0 siblings, 0 replies; 6+ messages in thread
From: Linus Torvalds @ 2021-05-25 17:28 UTC (permalink / raw)
  To: Aneesh Kumar K.V
  Cc: Nick Piggin, Linux-MM, Kalesh Singh, Joel Fernandes,
	Kirill A . Shutemov, Andrew Morton, linuxppc-dev

On Mon, May 24, 2021 at 10:34 PM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> @@ -221,6 +222,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
>                 spin_unlock(pvmw->pte_ptl);
>         if (pvmw->pmd_ptl)
>                 spin_unlock(pvmw->pmd_ptl);
> +       if (pvmw->pud_ptl)
> +               spin_unlock(pvmw->pud_ptl);
> +
>  }

You have this habit of adding odd whitespace..

But yes, this seems to be the right way to fix the races properly. The
pageout code is special, the pageout code is normally not critical, so
it's the pageout code that should go the extra mile to make up for the
fact that it doesn't hold the mmap_sem like good page table
modification codepaths do.

                Linus

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-05-25 17:29 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-05-25  8:33 [RFC PATCH 1/2] mm/mremap: Fix race between MOVE_PMD mremap and pageout Aneesh Kumar K.V
2021-05-25  8:33 ` Aneesh Kumar K.V
2021-05-25  8:33 ` [RFC PATCH 2/2] mm/mremap: Fix race between MOVE_PUD " Aneesh Kumar K.V
2021-05-25  8:33   ` Aneesh Kumar K.V
2021-05-25 17:28   ` Linus Torvalds
2021-05-25 17:28     ` Linus Torvalds

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