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Message-ID: <20230127194110.533103-15-surenb@google.com>
Date: Fri, 27 Jan 2023 11:40:51 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
vbabka@...e.cz, hannes@...xchg.org, mgorman@...hsingularity.net,
dave@...olabs.net, willy@...radead.org, liam.howlett@...cle.com,
peterz@...radead.org, ldufour@...ux.ibm.com, paulmck@...nel.org,
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dhowells@...hat.com, hughd@...gle.com, bigeasy@...utronix.de,
kent.overstreet@...ux.dev, punit.agrawal@...edance.com,
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leewalsh@...gle.com, posk@...gle.com, linux-mm@...ck.org,
linux-arm-kernel@...ts.infradead.org,
linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
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surenb@...gle.com
Subject: [PATCH v2 14/33] mm/khugepaged: write-lock VMA while collapsing a
huge page
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.
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
mm/khugepaged.c | 5 +++++
mm/rmap.c | 31 ++++++++++++++++---------------
2 files changed, 21 insertions(+), 15 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index eb38bd1b1b2f..b938b286cdc3 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1134,6 +1134,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
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,
@@ -1601,6 +1602,9 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
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
@@ -1806,6 +1810,7 @@ static int retract_page_tables(struct address_space *mapping, pgoff_t pgoff,
result = SCAN_PTE_UFFD_WP;
goto unlock_next;
}
+ vma_start_write(vma);
collapse_and_free_pmd(mm, vma, addr, pmd);
if (!cc->is_khugepaged && is_target)
result = set_huge_pmd(vma, addr, pmd, hpage);
diff --git a/mm/rmap.c b/mm/rmap.c
index 15ae24585fc4..8e1a2ad9ca53 100644
--- a/mm/rmap.c
+++ b/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
--
2.39.1
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