[PATCH] mm: unmap_vmas with inner ptlock

Remove the page_table_lock from around the calls to unmap_vmas, and replace
the pte_offset_map in zap_pte_range by pte_offset_map_lock: all callers are
now safe to descend without page_table_lock.

Don't attempt fancy locking for hugepages, just take page_table_lock in
unmap_hugepage_range.  Which makes zap_hugepage_range, and the hugetlb test in
zap_page_range, redundant: unmap_vmas calls unmap_hugepage_range anyway.  Nor
does unmap_vmas have much use for its mm arg now.

The tlb_start_vma and tlb_end_vma in unmap_page_range are now called without
page_table_lock: if they're implemented at all, they typically come down to
flush_cache_range (usually done outside page_table_lock) and flush_tlb_range
(which we already audited for the mprotect case).

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 6 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index fa35323a3c5b..5ecc2cf3e1d7 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1673,9 +1673,7 @@ static void unmap_region(struct mm_struct *mm,
         lru_add_drain();
         tlb = tlb_gather_mmu(mm, 0);
         update_hiwater_rss(mm);
-        spin_lock(&mm->page_table_lock);
-        unmap_vmas(&tlb, mm, vma, start, end, &nr_accounted, NULL);
-        spin_unlock(&mm->page_table_lock);
+        unmap_vmas(&tlb, vma, start, end, &nr_accounted, NULL);
         vm_unacct_memory(nr_accounted);
         free_pgtables(&tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,
                                  next? next->vm_start: 0);
@@ -1958,9 +1956,7 @@ void exit_mmap(struct mm_struct *mm)
         tlb = tlb_gather_mmu(mm, 1);
         /* Don't update_hiwater_rss(mm) here, do_exit already did */
         /* Use -1 here to ensure all VMAs in the mm are unmapped */
-        spin_lock(&mm->page_table_lock);
-        end = unmap_vmas(&tlb, mm, vma, 0, -1, &nr_accounted, NULL);
-        spin_unlock(&mm->page_table_lock);
+        end = unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL);
         vm_unacct_memory(nr_accounted);
         free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
         tlb_finish_mmu(tlb, 0, end);