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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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18
mm/mremap.c
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@@ -149,14 +149,18 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
if (pte_none(*old_pte))
continue;
/*
* We are remapping a dirty PTE, make sure to
* flush TLB before we drop the PTL for the
* old PTE or we may race with page_mkclean().
*/
if (pte_present(*old_pte) && pte_dirty(*old_pte))
force_flush = true;
pte = ptep_get_and_clear(mm, old_addr, old_pte);
/*
* If we are remapping a dirty PTE, make sure
* to flush TLB before we drop the PTL for the
* old PTE or we may race with page_mkclean().
*
* This check has to be done after we removed the
* old PTE from page tables or another thread may
* dirty it after the check and before the removal.
*/
if (pte_present(pte) && pte_dirty(pte))
force_flush = true;
pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
pte = move_soft_dirty_pte(pte);
set_pte_at(mm, new_addr, new_pte, pte);