The quilt patch titled
Subject: mm/khugepaged: write-lock VMA while collapsing a huge page
has been removed from the -mm tree. Its filename was
mm-khugepaged-write-lock-vma-while-collapsing-a-huge-page.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: mm/khugepaged: write-lock VMA while collapsing a huge page
Date: Mon, 27 Feb 2023 09:36:14 -0800
Protect VMA from concurrent page fault handler while collapsing a huge
page. Page fault handler needs a stable PMD to use PTL and relies on
per-VMA lock to prevent concurrent PMD changes. pmdp_collapse_flush(),
set_huge_pmd() and collapse_and_free_pmd() can modify a PMD, which will
not be detected by a page fault handler without proper locking.
Before this patch, page tables can be walked under any one of the
mmap_lock, the mapping lock, and the anon_vma lock; so when khugepaged
unlinks and frees page tables, it must ensure that all of those either are
locked or don't exist. This patch adds a fourth lock under which page
tables can be traversed, and so khugepaged must also lock out that one.
[surenb@xxxxxxxxxx: vm_lock/i_mmap_rwsem inversion in retract_page_tables]
Link: https://lkml.kernel.org/r/20230303213250.3555716-1-surenb@xxxxxxxxxx
[surenb@xxxxxxxxxx: build fix]
Link: https://lkml.kernel.org/r/CAJuCfpFjWhtzRE1X=J+_JjgJzNKhq-=JT8yTBSTHthwp0pqWZw@xxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20230227173632.3292573-16-surenb@xxxxxxxxxx
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 41 ++++++++++++++++++++++++++++++-----------
mm/khugepaged.c | 8 ++++++++
mm/rmap.c | 31 ++++++++++++++++---------------
3 files changed, 54 insertions(+), 26 deletions(-)
--- a/include/linux/mm.h~mm-khugepaged-write-lock-vma-while-collapsing-a-huge-page
+++ a/include/linux/mm.h
@@ -665,18 +665,23 @@ static inline void vma_end_read(struct v
rcu_read_unlock();
}
-static inline void vma_start_write(struct vm_area_struct *vma)
+static bool __is_vma_write_locked(struct vm_area_struct *vma, int *mm_lock_seq)
{
- int mm_lock_seq;
-
mmap_assert_write_locked(vma->vm_mm);
/*
* current task is holding mmap_write_lock, both vma->vm_lock_seq and
* mm->mm_lock_seq can't be concurrently modified.
*/
- mm_lock_seq = READ_ONCE(vma->vm_mm->mm_lock_seq);
- if (vma->vm_lock_seq == mm_lock_seq)
+ *mm_lock_seq = READ_ONCE(vma->vm_mm->mm_lock_seq);
+ return (vma->vm_lock_seq == *mm_lock_seq);
+}
+
+static inline void vma_start_write(struct vm_area_struct *vma)
+{
+ int mm_lock_seq;
+
+ if (__is_vma_write_locked(vma, &mm_lock_seq))
return;
down_write(&vma->lock);
@@ -684,14 +689,26 @@ static inline void vma_start_write(struc
up_write(&vma->lock);
}
+static inline bool vma_try_start_write(struct vm_area_struct *vma)
+{
+ int mm_lock_seq;
+
+ if (__is_vma_write_locked(vma, &mm_lock_seq))
+ return true;
+
+ if (!down_write_trylock(&vma->vm_lock->lock))
+ return false;
+
+ vma->vm_lock_seq = mm_lock_seq;
+ up_write(&vma->vm_lock->lock);
+ return true;
+}
+
static inline void vma_assert_write_locked(struct vm_area_struct *vma)
{
- mmap_assert_write_locked(vma->vm_mm);
- /*
- * current task is holding mmap_write_lock, both vma->vm_lock_seq and
- * mm->mm_lock_seq can't be concurrently modified.
- */
- VM_BUG_ON_VMA(vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq), vma);
+ int mm_lock_seq;
+
+ VM_BUG_ON_VMA(!__is_vma_write_locked(vma, &mm_lock_seq), vma);
}
#else /* CONFIG_PER_VMA_LOCK */
@@ -701,6 +718,8 @@ static inline bool vma_start_read(struct
{ return false; }
static inline void vma_end_read(struct vm_area_struct *vma) {}
static inline void vma_start_write(struct vm_area_struct *vma) {}
+static inline bool vma_try_start_write(struct vm_area_struct *vma)
+ { return true; }
static inline void vma_assert_write_locked(struct vm_area_struct *vma) {}
#endif /* CONFIG_PER_VMA_LOCK */
--- a/mm/khugepaged.c~mm-khugepaged-write-lock-vma-while-collapsing-a-huge-page
+++ a/mm/khugepaged.c
@@ -1056,6 +1056,7 @@ static int collapse_huge_page(struct mm_
if (result != SCAN_SUCCEED)
goto out_up_write;
+ vma_start_write(vma);
anon_vma_lock_write(vma->anon_vma);
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, address,
@@ -1517,6 +1518,9 @@ int collapse_pte_mapped_thp(struct mm_st
goto drop_hpage;
}
+ /* Lock the vma before taking i_mmap and page table locks */
+ vma_start_write(vma);
+
/*
* We need to lock the mapping so that from here on, only GUP-fast and
* hardware page walks can access the parts of the page tables that
@@ -1694,6 +1698,10 @@ static int retract_page_tables(struct ad
result = SCAN_PTE_MAPPED_HUGEPAGE;
if ((cc->is_khugepaged || is_target) &&
mmap_write_trylock(mm)) {
+ /* trylock for the same lock inversion as above */
+ if (!vma_try_start_write(vma))
+ goto unlock_next;
+
/*
* Re-check whether we have an ->anon_vma, because
* collapse_and_free_pmd() requires that either no
--- a/mm/rmap.c~mm-khugepaged-write-lock-vma-while-collapsing-a-huge-page
+++ a/mm/rmap.c
@@ -25,21 +25,22 @@
* mapping->invalidate_lock (in filemap_fault)
* page->flags PG_locked (lock_page)
* hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share, see hugetlbfs below)
- * mapping->i_mmap_rwsem
- * anon_vma->rwsem
- * mm->page_table_lock or pte_lock
- * swap_lock (in swap_duplicate, swap_info_get)
- * mmlist_lock (in mmput, drain_mmlist and others)
- * mapping->private_lock (in block_dirty_folio)
- * folio_lock_memcg move_lock (in block_dirty_folio)
- * i_pages lock (widely used)
- * lruvec->lru_lock (in folio_lruvec_lock_irq)
- * inode->i_lock (in set_page_dirty's __mark_inode_dirty)
- * bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
- * sb_lock (within inode_lock in fs/fs-writeback.c)
- * i_pages lock (widely used, in set_page_dirty,
- * in arch-dependent flush_dcache_mmap_lock,
- * within bdi.wb->list_lock in __sync_single_inode)
+ * vma_start_write
+ * mapping->i_mmap_rwsem
+ * anon_vma->rwsem
+ * mm->page_table_lock or pte_lock
+ * swap_lock (in swap_duplicate, swap_info_get)
+ * mmlist_lock (in mmput, drain_mmlist and others)
+ * mapping->private_lock (in block_dirty_folio)
+ * folio_lock_memcg move_lock (in block_dirty_folio)
+ * i_pages lock (widely used)
+ * lruvec->lru_lock (in folio_lruvec_lock_irq)
+ * inode->i_lock (in set_page_dirty's __mark_inode_dirty)
+ * bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
+ * sb_lock (within inode_lock in fs/fs-writeback.c)
+ * i_pages lock (widely used, in set_page_dirty,
+ * in arch-dependent flush_dcache_mmap_lock,
+ * within bdi.wb->list_lock in __sync_single_inode)
*
* anon_vma->rwsem,mapping->i_mmap_rwsem (memory_failure, collect_procs_anon)
* ->tasklist_lock
_
Patches currently in -mm which might be from surenb@xxxxxxxxxx are
