[PATCH] btrfs: fix possible deadlock by clearing __GFP_FS flag

[Miao Xie]

Using the GFP_HIGHUSER_MOVABLE flag to allocate the metadata's page may cause
deadlock.
  Task1                                 Kswap0 task
  open()
    ...
    btrfs_search_slot()
      ...
      btrfs_cow_block()
        ...
        alloc_page()
          wait for reclaiming
                                        shrink_slab()
                                          ...
                                          shrink_icache_memory()
                                            ...
                                            btrfs_evict_inode()
                                              ...
                                              btrfs_search_slot()

If the path is locked by task1, the deadlock happens.

So the btree's page cache is different with the file's page cache, it can not
allocate pages by GFP_HIGHUSER_MOVABLE flag, we must clear __GFP_FS flag in
GFP_HIGHUSER_MOVABLE flag.

Reported-by: Itaru Kitayama <kitay...@cl.bb4u.ne.jp>
Signed-off-by: Miao Xie <mi...@cn.fujitsu.com>
---
 fs/btrfs/disk-io.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3e1ea3e..cf55fa0 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1632,6 +1632,8 @@ struct btrfs_root *open_ctree(struct super_block *sb,
                goto fail_bdi;
        }
 
+       fs_info->btree_inode->i_mapping->flags &= ~__GFP_FS;
+
        INIT_RADIX_TREE(&fs_info->fs_roots_radix, GFP_ATOMIC);
        INIT_LIST_HEAD(&fs_info->trans_list);
        INIT_LIST_HEAD(&fs_info->dead_roots);
-- 
1.7.4
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html