mm: fix sleeping function warning from __put_anon_vma

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 9c3e77396d1a..10aef960d3d0 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -103,6 +103,7 @@ static inline void anon_vma_free(struct anon_vma *anon_vma)
          * LOCK should suffice since the actual taking of the lock must
          * happen _before_ what follows.
          */
+        might_sleep();
         if (rwsem_is_locked(&anon_vma->root->rwsem)) {
                 anon_vma_lock_write(anon_vma);
                 anon_vma_unlock_write(anon_vma);
@@ -426,8 +427,9 @@ struct anon_vma *page_get_anon_vma(struct page *page)
          * above cannot corrupt).
          */
         if (!page_mapped(page)) {
+                rcu_read_unlock();
                 put_anon_vma(anon_vma);
-                anon_vma = NULL;
+                return NULL;
         }
 out:
         rcu_read_unlock();
@@ -477,9 +479,9 @@ struct anon_vma *page_lock_anon_vma_read(struct page *page)
         }
 
         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 */