[PATCH 3.4 12/43] mm: fix sleeping function warning from __put_anon_vma

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hugh Dickins <hughd@google.com>

commit 7f39dda9d86fb4f4f17af0de170decf125726f8c upstream.

Trinity reports BUG:

  sleeping function called from invalid context at kernel/locking/rwsem.c:47
  in_atomic(): 0, irqs_disabled(): 0, pid: 5787, name: trinity-c27

__might_sleep < down_write < __put_anon_vma < page_get_anon_vma <
migrate_pages < compact_zone < compact_zone_order < try_to_compact_pages ..

Right, since conversion to mutex then rwsem, we should not put_anon_vma()
from inside an rcu_read_lock()ed section: fix the two places that did so.
And add might_sleep() to anon_vma_free(), as suggested by Peter Zijlstra.

Fixes: 88c22088bf23 ("mm: optimize page_lock_anon_vma() fast-path")
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/rmap.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -103,6 +103,7 @@ static inline void anon_vma_free(struct
 	 * LOCK should suffice since the actual taking of the lock must
 	 * happen _before_ what follows.
 	 */
+	might_sleep();
 	if (mutex_is_locked(&anon_vma->root->mutex)) {
 		anon_vma_lock(anon_vma);
 		anon_vma_unlock(anon_vma);
@@ -476,8 +477,9 @@ struct anon_vma *page_get_anon_vma(struc
 	 * above cannot corrupt).
 	 */
 	if (!page_mapped(page)) {
+		rcu_read_unlock();
 		put_anon_vma(anon_vma);
-		anon_vma = NULL;
+		return NULL;
 	}
 out:
 	rcu_read_unlock();
@@ -527,9 +529,9 @@ struct anon_vma *page_lock_anon_vma(stru
 	}
 
 	if (!page_mapped(page)) {
+		rcu_read_unlock();
 		put_anon_vma(anon_vma);
-		anon_vma = NULL;
-		goto out;
+		return NULL;
 	}
 
 	/* we pinned the anon_vma, its safe to sleep */