---------- Forwarded message ----------
Date: Tue, 8 Jun 2021 21:00:12 -0700 (PDT)
From: Hugh Dickins <hughd@xxxxxxxxxx>
To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>,
Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>,
Yang Shi <shy828301@xxxxxxxxx>, Wang Yugui <wangyugui@xxxxxxxxxxxx>,
Matthew Wilcox <willy@xxxxxxxxxxxxx>,
Naoya Horiguchi <naoya.horiguchi@xxxxxxx>,
Alistair Popple <apopple@xxxxxxxxxx>, Ralph Campbell <rcampbell@xxxxxxxxxx>,
Zi Yan <ziy@xxxxxxxxxx>, Miaohe Lin <linmiaohe@xxxxxxxxxx>,
Minchan Kim <minchan@xxxxxxxxxx>, Jue Wang <juew@xxxxxxxxxx>,
Peter Xu <peterx@xxxxxxxxxx>, Jan Kara <jack@xxxxxxx>,
Shakeel Butt <shakeelb@xxxxxxxxxx>, Oscar Salvador <osalvador@xxxxxxx>
Subject: [PATCH v2 01/10] mm/thp: fix __split_huge_pmd_locked() on shmem
migration entry
Stressing huge tmpfs page migration racing hole punch often crashed on the
VM_BUG_ON(!pmd_present) in pmdp_huge_clear_flush(), with DEBUG_VM=y kernel;
or shortly afterwards, on a bad dereference in __split_huge_pmd_locked()
when DEBUG_VM=n. They forgot to allow for pmd migration entries in the
non-anonymous case.
Full disclosure: those particular experiments were on a kernel with more
relaxed mmap_lock and i_mmap_rwsem locking, and were not repeated on the
vanilla kernel: it is conceivable that stricter locking happens to avoid
those cases, or makes them less likely; but __split_huge_pmd_locked()
already allowed for pmd migration entries when handling anonymous THPs,
so this commit brings the shmem and file THP handling into line.
And while there: use old_pmd rather than _pmd, as in the following blocks;
and make it clearer to the eye that the !vma_is_anonymous() block is
self-contained, making an early return after accounting for unmapping.
Fixes: e71769ae5260 ("mm: enable thp migration for shmem thp")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
v2: omit is_huge_zero_pmd() mods (done differently in next), per Kirill
mm/huge_memory.c | 27 ++++++++++++++++++---------
mm/pgtable-generic.c | 5 ++---
2 files changed, 20 insertions(+), 12 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 63ed6b25deaa..42cfefc6e66e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2044,7 +2044,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
count_vm_event(THP_SPLIT_PMD);
if (!vma_is_anonymous(vma)) {
- _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
+ old_pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
/*
* We are going to unmap this huge page. So
* just go ahead and zap it
@@ -2053,16 +2053,25 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
zap_deposited_table(mm, pmd);
if (vma_is_special_huge(vma))
return;
- page = pmd_page(_pmd);
- if (!PageDirty(page) && pmd_dirty(_pmd))
- set_page_dirty(page);
- if (!PageReferenced(page) && pmd_young(_pmd))
- SetPageReferenced(page);
- page_remove_rmap(page, true);
- put_page(page);
+ if (unlikely(is_pmd_migration_entry(old_pmd))) {
+ swp_entry_t entry;
+
+ entry = pmd_to_swp_entry(old_pmd);
+ page = migration_entry_to_page(entry);
+ } else {
+ page = pmd_page(old_pmd);
+ if (!PageDirty(page) && pmd_dirty(old_pmd))
+ set_page_dirty(page);
+ if (!PageReferenced(page) && pmd_young(old_pmd))
+ SetPageReferenced(page);
+ page_remove_rmap(page, true);
+ put_page(page);
+ }
add_mm_counter(mm, mm_counter_file(page), -HPAGE_PMD_NR);
return;
- } else if (pmd_trans_huge(*pmd) && is_huge_zero_pmd(*pmd)) {
+ }
+
+ if (pmd_trans_huge(*pmd) && is_huge_zero_pmd(*pmd)) {
/*
* FIXME: Do we want to invalidate secondary mmu by calling
* mmu_notifier_invalidate_range() see comments below inside
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index c2210e1cdb51..4e640baf9794 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -135,9 +135,8 @@ pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
{
pmd_t pmd;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
- VM_BUG_ON(!pmd_present(*pmdp));
- /* Below assumes pmd_present() is true */
- VM_BUG_ON(!pmd_trans_huge(*pmdp) && !pmd_devmap(*pmdp));
+ VM_BUG_ON(pmd_present(*pmdp) && !pmd_trans_huge(*pmdp) &&
+ !pmd_devmap(*pmdp));
pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
return pmd;
--
2.26.2
