[PATCH] aio: fix error-path mm leak in ioctx_alloc

From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

ioctx_alloc() leaks an mm->mm_count ref on an error path.

fs/aio.c

@@ -258,6 +258,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
 	return ERR_PTR(-EAGAIN);
 
 out_freectx:
+	mmdrop(mm);
 	kmem_cache_free(kioctx_cachep, ctx);
 	ctx = ERR_PTR(-ENOMEM);