The patch titled
Subject: huge pagecache: mmap_sem is unlocked when truncation splits pmd
has been added to the -mm tree. Its filename is
huge-pagecache-mmap_sem-is-unlocked-when-truncation-splits-pmd.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/huge-pagecache-mmap_sem-is-unlocked-when-truncation-splits-pmd.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/huge-pagecache-mmap_sem-is-unlocked-when-truncation-splits-pmd.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: huge pagecache: mmap_sem is unlocked when truncation splits pmd
zap_pmd_range()'s CONFIG_DEBUG_VM !rwsem_is_locked(&mmap_sem) BUG() will
be invalid with huge pagecache, in whatever way it is implemented:
truncation of a hugely-mapped file to an unhugely-aligned size would
easily hit it.
(Although anon THP could in principle apply khugepaged to private file
mappings, which are not excluded by the MADV_HUGEPAGE restrictions, in
practice there's a vm_ops check which excludes them, so it never hits this
BUG() - there's no interface to "truncate" an anonymous mapping.)
We could complicate the test, to check i_mmap_rwsem also when there's a
vm_file; but my inclination was to make zap_pmd_range() more readable by
simply deleting this check. A search has shown no report of the issue in
the years since commit e0897d75f0b2 ("mm, thp: print useful information
when mmap_sem is unlocked in zap_pmd_range") expanded it from VM_BUG_ON()
- though I cannot point to what commit I would say then fixed the issue.
But there are a couple of other patches now floating around, neither yet
in the tree: let's agree to retain the check as a VM_BUG_ON_VMA(), as
Matthew Wilcox has done; but subject to a vma_is_anonymous() check, as
Kirill Shutemov has done. And let's get this in, without waiting for any
particular huge pagecache implementation to reach the tree.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andres Lagar-Cavilla <andreslc@xxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxx>
Cc: Ning Qu <quning@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Andres Lagar-Cavilla <andreslc@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)
diff -puN mm/memory.c~huge-pagecache-mmap_sem-is-unlocked-when-truncation-splits-pmd mm/memory.c
--- a/mm/memory.c~huge-pagecache-mmap_sem-is-unlocked-when-truncation-splits-pmd
+++ a/mm/memory.c
@@ -1222,15 +1222,8 @@ static inline unsigned long zap_pmd_rang
next = pmd_addr_end(addr, end);
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
if (next - addr != HPAGE_PMD_SIZE) {
-#ifdef CONFIG_DEBUG_VM
- if (!rwsem_is_locked(&tlb->mm->mmap_sem)) {
- pr_err("%s: mmap_sem is unlocked! addr=0x%lx end=0x%lx vma->vm_start=0x%lx vma->vm_end=0x%lx\n",
- __func__, addr, end,
- vma->vm_start,
- vma->vm_end);
- BUG();
- }
-#endif
+ VM_BUG_ON_VMA(vma_is_anonymous(vma) &&
+ !rwsem_is_locked(&tlb->mm->mmap_sem), vma);
split_huge_pmd(vma, pmd, addr);
} else if (zap_huge_pmd(tlb, vma, pmd, addr))
goto next;
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-update_lru_size-warn-and-reset-bad-lru_size.patch
mm-update_lru_size-do-the-__mod_zone_page_state.patch
mm-use-__setpageswapbacked-and-dont-clearpageswapbacked.patch
tmpfs-preliminary-minor-tidyups.patch
mm-proc-sys-vm-stat_refresh-to-force-vmstat-update.patch
huge-mm-move_huge_pmd-does-not-need-new_vma.patch
huge-pagecache-extend-mremap-pmd-rmap-lockout-to-files.patch
huge-pagecache-mmap_sem-is-unlocked-when-truncation-splits-pmd.patch
arch-fix-has_transparent_hugepage.patch
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