mm: use refcounts for page_lock_anon_vma()
Convert page_lock_anon_vma() over to use refcounts. This is done to
prepare for the conversion of anon_vma from spinlock to mutex.
Sadly this inceases the cost of page_lock_anon_vma() from one to two
atomics, a follow up patch addresses this, lets keep that simple for now.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Miller <davem@davemloft.net>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/rmap.c b/mm/rmap.c
index cc140811a..d271845 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -337,9 +337,9 @@
* that the anon_vma pointer from page->mapping is valid if there is a
* mapcount, we can dereference the anon_vma after observing those.
*/
-struct anon_vma *page_lock_anon_vma(struct page *page)
+struct anon_vma *page_get_anon_vma(struct page *page)
{
- struct anon_vma *anon_vma, *root_anon_vma;
+ struct anon_vma *anon_vma = NULL;
unsigned long anon_mapping;
rcu_read_lock();
@@ -350,30 +350,42 @@
goto out;
anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
- root_anon_vma = ACCESS_ONCE(anon_vma->root);
- spin_lock(&root_anon_vma->lock);
+ if (!atomic_inc_not_zero(&anon_vma->refcount)) {
+ anon_vma = NULL;
+ goto out;
+ }
/*
* If this page is still mapped, then its anon_vma cannot have been
- * freed. But if it has been unmapped, we have no security against
- * the anon_vma structure being freed and reused (for another anon_vma:
- * SLAB_DESTROY_BY_RCU guarantees that - so the spin_lock above cannot
- * corrupt): with anon_vma_prepare() or anon_vma_fork() redirecting
- * anon_vma->root before page_unlock_anon_vma() is called to unlock.
+ * freed. But if it has been unmapped, we have no security against the
+ * anon_vma structure being freed and reused (for another anon_vma:
+ * SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()
+ * above cannot corrupt).
*/
- if (page_mapped(page))
- return anon_vma;
-
- spin_unlock(&root_anon_vma->lock);
+ if (!page_mapped(page)) {
+ put_anon_vma(anon_vma);
+ anon_vma = NULL;
+ }
out:
rcu_read_unlock();
- return NULL;
+
+ return anon_vma;
+}
+
+struct anon_vma *page_lock_anon_vma(struct page *page)
+{
+ struct anon_vma *anon_vma = page_get_anon_vma(page);
+
+ if (anon_vma)
+ anon_vma_lock(anon_vma);
+
+ return anon_vma;
}
void page_unlock_anon_vma(struct anon_vma *anon_vma)
{
anon_vma_unlock(anon_vma);
- rcu_read_unlock();
+ put_anon_vma(anon_vma);
}
/*