mm: fix sleeping function warning from __put_anon_vma

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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/mm/rmap.c b/mm/rmap.c
index 9ac405b..ae27d95 100644 (file)
--- 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.
         */
         * 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);
        if (mutex_is_locked(&anon_vma->root->mutex)) {
                anon_vma_lock(anon_vma);
                anon_vma_unlock(anon_vma);


@@ -434,8 +435,9 @@ struct anon_vma *page_get_anon_vma(struct page *page)
         * above cannot corrupt).
         */
        if (!page_mapped(page)) {
         * above cannot corrupt).
         */
        if (!page_mapped(page)) {

+               rcu_read_unlock();

                put_anon_vma(anon_vma);
                put_anon_vma(anon_vma);

-               anon_vma = NULL;
+               return NULL;

        }
 out:
        rcu_read_unlock();
        }
 out:
        rcu_read_unlock();


@@ -485,9 +487,9 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
        }
 
        if (!page_mapped(page)) {
        }
 
        if (!page_mapped(page)) {

+               rcu_read_unlock();

                put_anon_vma(anon_vma);
                put_anon_vma(anon_vma);

-               anon_vma = NULL;
-               goto out;
+               return NULL;

        }
 
        /* we pinned the anon_vma, its safe to sleep */
        }
 
        /* we pinned the anon_vma, its safe to sleep */