cgroup: Merge branch 'for-4.3-fixes' into for-4.4

Pull to receive 9badce000e2c ("cgroup, writeback: don't enable cgroup
writeback on traditional hierarchies").  The commit adds
cgroup_on_dfl() usages in include/linux/backing-dev.h thus causing a
silent conflict with 9e10a130d9b6 ("cgroup: replace cgroup_on_dfl()
tests in controllers with cgroup_subsys_on_dfl()").  The conflict is
fixed during this merge.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 8 insertions, 2 deletions

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 5a5d79ee256f..08d9a8eac42c 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -252,13 +252,19 @@ int inode_congested(struct inode *inode, int cong_bits);
  * @inode: inode of interest
  *
  * cgroup writeback requires support from both the bdi and filesystem.
- * Test whether @inode has both.
+ * Also, both memcg and iocg have to be on the default hierarchy.  Test
+ * whether all conditions are met.
+ *
+ * Note that the test result may change dynamically on the same inode
+ * depending on how memcg and iocg are configured.
  */
 static inline bool inode_cgwb_enabled(struct inode *inode)
 {
         struct backing_dev_info *bdi = inode_to_bdi(inode);
 
-        return bdi_cap_account_dirty(bdi) &&
+        return cgroup_subsys_on_dfl(memory_cgrp_subsys) &&
+                cgroup_subsys_on_dfl(io_cgrp_subsys) &&
+                bdi_cap_account_dirty(bdi) &&
                 (bdi->capabilities & BDI_CAP_CGROUP_WRITEBACK) &&
                 (inode->i_sb->s_iflags & SB_I_CGROUPWB);
 }