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authorNick Piggin <npiggin@suse.de>2007-07-19 01:47:22 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-19 10:04:41 -0700
commit79352894b28550ee0eee919149f57626ec1b3572 (patch)
tree849e6aa148c69b9df3920199255ca14792eeffa2 /mm/memory.c
parent83c54070ee1a2d05c89793884bea1a03f2851ed4 (diff)
mm: fix clear_page_dirty_for_io vs fault race
Fix msync data loss and (less importantly) dirty page accounting inaccuracies due to the race remaining in clear_page_dirty_for_io(). The deleted comment explains what the race was, and the added comments explain how it is fixed. Signed-off-by: Nick Piggin <npiggin@suse.de> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 61d51da7e17..50dd3d1f4d1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1765,6 +1765,15 @@ gotten:
unlock:
pte_unmap_unlock(page_table, ptl);
if (dirty_page) {
+ /*
+ * Yes, Virginia, this is actually required to prevent a race
+ * with clear_page_dirty_for_io() from clearing the page dirty
+ * bit after it clear all dirty ptes, but before a racing
+ * do_wp_page installs a dirty pte.
+ *
+ * do_no_page is protected similarly.
+ */
+ wait_on_page_locked(dirty_page);
set_page_dirty_balance(dirty_page);
put_page(dirty_page);
}