[PATCH] mm: fix rss and mmlist locking

A couple of oddities were guarded by page_table_lock, no longer properly
guarded when that is split.

The mm_counters of file_rss and anon_rss: make those an atomic_t, or an
atomic64_t if the architecture supports it, in such a case.  Definitions by
courtesy of Christoph Lameter: who spent considerable effort on more scalable
ways of counting, but found insufficient benefit in practice.

And adding an mm with swap to the mmlist for swapoff: the list is well-
guarded by its own lock, but the list_empty check now has to be repeated
inside it.

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, 3 insertions, 1 deletions

diff --git a/mm/memory.c b/mm/memory.c
index e9ef599498b5..d68421dd64ef 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -372,7 +372,9 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 			/* make sure dst_mm is on swapoff's mmlist. */
 			if (unlikely(list_empty(&dst_mm->mmlist))) {
 				spin_lock(&mmlist_lock);
-				list_add(&dst_mm->mmlist, &src_mm->mmlist);
+				if (list_empty(&dst_mm->mmlist))
+					list_add(&dst_mm->mmlist,
+						 &src_mm->mmlist);
 				spin_unlock(&mmlist_lock);
 			}
 		}