khugepaged: collapse_pte_mapped_thp() protect the pmd lock
commit119a5fc161
upstream. When retract_page_tables() removes a page table to make way for a huge pmd, it holds huge page lock, i_mmap_lock_write, mmap_write_trylock and pmd lock; but when collapse_pte_mapped_thp() does the same (to handle the case when the original mmap_write_trylock had failed), only mmap_write_trylock and pmd lock are held. That's not enough. One machine has twice crashed under load, with "BUG: spinlock bad magic" and GPF on 6b6b6b6b6b6b6b6b. Examining the second crash, page_vma_mapped_walk_done()'s spin_unlock of pvmw->ptl (serving page_referenced() on a file THP, that had found a page table at *pmd) discovers that the page table page and its lock have already been freed by the time it comes to unlock. Follow the example of retract_page_tables(), but we only need one of huge page lock or i_mmap_lock_write to secure against this: because it's the narrower lock, and because it simplifies collapse_pte_mapped_thp() to know the hpage earlier, choose to rely on huge page lock here. Fixes:27e1f82731
("khugepaged: enable collapse pmd for pte-mapped THP") Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Song Liu <songliubraving@fb.com> Cc: <stable@vger.kernel.org> [5.4+] Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008021213070.27773@eggly.anvils Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -1294,7 +1294,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
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{
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unsigned long haddr = addr & HPAGE_PMD_MASK;
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struct vm_area_struct *vma = find_vma(mm, haddr);
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struct page *hpage = NULL;
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struct page *hpage;
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pte_t *start_pte, *pte;
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pmd_t *pmd, _pmd;
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spinlock_t *ptl;
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@ -1314,9 +1314,17 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
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if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
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return;
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hpage = find_lock_page(vma->vm_file->f_mapping,
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linear_page_index(vma, haddr));
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if (!hpage)
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return;
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if (!PageHead(hpage))
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goto drop_hpage;
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pmd = mm_find_pmd(mm, haddr);
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if (!pmd)
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return;
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goto drop_hpage;
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start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
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@ -1335,30 +1343,11 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
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page = vm_normal_page(vma, addr, *pte);
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if (!page || !PageCompound(page))
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goto abort;
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if (!hpage) {
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hpage = compound_head(page);
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/*
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* The mapping of the THP should not change.
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*
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* Note that uprobe, debugger, or MAP_PRIVATE may
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* change the page table, but the new page will
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* not pass PageCompound() check.
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*/
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if (WARN_ON(hpage->mapping != vma->vm_file->f_mapping))
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goto abort;
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}
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/*
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* Confirm the page maps to the correct subpage.
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*
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* Note that uprobe, debugger, or MAP_PRIVATE may change
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* the page table, but the new page will not pass
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* PageCompound() check.
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* Note that uprobe, debugger, or MAP_PRIVATE may change the
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* page table, but the new page will not be a subpage of hpage.
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*/
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if (WARN_ON(hpage + i != page))
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if (hpage + i != page)
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goto abort;
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count++;
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}
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@ -1377,7 +1366,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
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pte_unmap_unlock(start_pte, ptl);
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/* step 3: set proper refcount and mm_counters. */
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if (hpage) {
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if (count) {
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page_ref_sub(hpage, count);
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add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
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}
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@ -1388,10 +1377,15 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
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spin_unlock(ptl);
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mm_dec_nr_ptes(mm);
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pte_free(mm, pmd_pgtable(_pmd));
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drop_hpage:
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unlock_page(hpage);
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put_page(hpage);
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return;
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abort:
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pte_unmap_unlock(start_pte, ptl);
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goto drop_hpage;
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}
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static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
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