The patch titled
Subject: mm/thp: fix __split_huge_pmd_locked() on shmem migration entry
has been added to the -mm tree. Its filename is
mm-thp-fix-__split_huge_pmd_locked-on-shmem-migration-entry.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-fix-__split_huge_pmd_locked-on-shmem-migration-entry.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-fix-__split_huge_pmd_locked-on-shmem-migration-entry.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm/thp: fix __split_huge_pmd_locked() on shmem migration entry
Patch series "mm/thp: fix THP splitting unmap BUGs and related", v10.
Here is v2 batch of long-standing THP bug fixes that I had not got around
to sending before, but prompted now by Wang Yugui's report
https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@xxxxxxxxxxxx/
Wang Yugui has tested a rollup of these fixes applied to 5.10.39, and they
have done no harm, but have *not* fixed that issue: something more is
needed and I have no idea of what.
This patch (of 7):
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.
Link: https://lkml.kernel.org/r/af88612-1473-2eaa-903-8d1a448b26@xxxxxxxxxx
Link: https://lkml.kernel.org/r/dd221a99-efb3-cd1d-6256-7e646af29314@xxxxxxxxxx
Fixes: e71769ae5260 ("mm: enable thp migration for shmem thp")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Wang Yugui <wangyugui@xxxxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Jue Wang <juew@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 27 ++++++++++++++++++---------
mm/pgtable-generic.c | 5 ++---
2 files changed, 20 insertions(+), 12 deletions(-)
--- a/mm/huge_memory.c~mm-thp-fix-__split_huge_pmd_locked-on-shmem-migration-entry
+++ a/mm/huge_memory.c
@@ -2044,7 +2044,7 @@ static void __split_huge_pmd_locked(stru
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(stru
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
--- a/mm/pgtable-generic.c~mm-thp-fix-__split_huge_pmd_locked-on-shmem-migration-entry
+++ a/mm/pgtable-generic.c
@@ -135,9 +135,8 @@ pmd_t pmdp_huge_clear_flush(struct vm_ar
{
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;
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-thp-fix-__split_huge_pmd_locked-on-shmem-migration-entry.patch
mm-thp-make-is_huge_zero_pmd-safe-and-quicker.patch
mm-thp-try_to_unmap-use-ttu_sync-for-safe-splitting.patch
mm-thp-fix-vma_address-if-virtual-address-below-file-offset.patch
mm-thp-unmap_mapping_page-to-fix-thp-truncate_cleanup_page.patch
mm-page_vma_mapped_walk-use-page-for-pvmw-page.patch
mm-page_vma_mapped_walk-settle-pagehuge-on-entry.patch
mm-page_vma_mapped_walk-use-pmd_read_atomic.patch
mm-page_vma_mapped_walk-use-pmde-for-pvmw-pmd.patch
mm-page_vma_mapped_walk-prettify-pvmw_migration-block.patch
mm-page_vma_mapped_walk-crossing-page-table-boundary.patch
mm-page_vma_mapped_walk-add-a-level-of-indentation.patch
mm-page_vma_mapped_walk-use-goto-instead-of-while-1.patch
mm-page_vma_mapped_walk-get-vma_address_end-earlier.patch
mm-thp-fix-page_vma_mapped_walk-if-thp-mapped-by-ptes.patch
mm-thp-another-pvmw_sync-fix-in-page_vma_mapped_walk.patch
mm-thp-remap_page-is-only-needed-on-anonymous-thp.patch
mm-hwpoison_user_mappings-try_to_unmap-with-ttu_sync.patch
