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mremap: move_ptes: check pte dirty after its removal

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Linus found there still is a race in mremap after commit 5d1904204c
("mremap: fix race between mremap() and page cleanning").

As described by Linus:
 "the issue is that another thread might make the pte be dirty (in the
  hardware walker, so no locking of ours will make any difference)
  *after* we checked whether it was dirty, but *before* we removed it
  from the page tables"

Fix it by moving the check after we removed it from the page table.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Aaron Lu
2016-11-29 13:27:31 +08:00
committed by Linus Torvalds
parent 88abd8249e
commit a2ce2666aa
2 changed files with 13 additions and 9 deletions
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4
mm/huge_memory.c
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@@ -1456,9 +1456,9 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
new_ptl = pmd_lockptr(mm, new_pmd);
if (new_ptl != old_ptl)
spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
if (pmd_present(*old_pmd) && pmd_dirty(*old_pmd))
force_flush = true;
pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
if (pmd_present(pmd) && pmd_dirty(pmd))
force_flush = true;
VM_BUG_ON(!pmd_none(*new_pmd));
if (pmd_move_must_withdraw(new_ptl, old_ptl) &&