bdi: Unify bdi->wb_list handling for root wb_writeback

BugLink: http://bugs.launchpad.net/bugs/1659111
Currently root wb_writeback structure is added to bdi->wb_list in
bdi_init() and never removed. That is different from all other
wb_writeback structures which get added to the list when created and
removed from it before wb_shutdown().

So move list addition of root bdi_writeback to bdi_register() and list
removal of all wb_writeback structures to wb_shutdown(). That way a
wb_writeback structure is on bdi->wb_list if and only if it can handle
writeback and it will make it easier for us to handle shutdown of all
wb_writeback structures in bdi_unregister().

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit e8cb72b322cf4a729633b7e2080fbeab477f6ea2)
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index eecae12c3d35338a4dbad497f49a96f46e8e268c..b809899e92294befa30e4fce53bf4f06be98ee06 100644 (file)
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -344,6 +344,8 @@ out_put_bdi:
        return err;
 }
 
+static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb);
+
 /*
  * Remove bdi from the global list and shutdown any threads we have running
  */
@@ -357,6 +359,7 @@ static void wb_shutdown(struct bdi_writeback *wb)
        }
        spin_unlock_bh(&wb->work_lock);
 
+       cgwb_remove_from_bdi_list(wb);
        /*
         * Drain work list and shutdown the delayed_work.  !WB_registered
         * tells wb_workfn() that @wb is dying and its work_list needs to
@@ -490,10 +493,6 @@ static void cgwb_release_workfn(struct work_struct *work)
                                                release_work);
        struct backing_dev_info *bdi = wb->bdi;
 
-       spin_lock_irq(&cgwb_lock);
-       list_del_rcu(&wb->bdi_node);
-       spin_unlock_irq(&cgwb_lock);
-
        wb_shutdown(wb);
 
        css_put(wb->memcg_css);
@@ -525,6 +524,13 @@ static void cgwb_kill(struct bdi_writeback *wb)
        percpu_ref_kill(&wb->refcnt);
 }
 
+static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
+{
+       spin_lock_irq(&cgwb_lock);
+       list_del_rcu(&wb->bdi_node);
+       spin_unlock_irq(&cgwb_lock);
+}
+
 static int cgwb_create(struct backing_dev_info *bdi,
                       struct cgroup_subsys_state *memcg_css, gfp_t gfp)
 {
@@ -765,6 +771,13 @@ static void cgwb_bdi_exit(struct backing_dev_info *bdi)
        spin_unlock_irq(&cgwb_lock);
 }
 
+static void cgwb_bdi_register(struct backing_dev_info *bdi)
+{
+       spin_lock_irq(&cgwb_lock);
+       list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
+       spin_unlock_irq(&cgwb_lock);
+}
+
 #else  /* CONFIG_CGROUP_WRITEBACK */
 
 static int cgwb_bdi_init(struct backing_dev_info *bdi)
@@ -792,6 +805,16 @@ static void cgwb_bdi_exit(struct backing_dev_info *bdi)
        wb_congested_put(bdi->wb_congested);
 }
 
+static void cgwb_bdi_register(struct backing_dev_info *bdi)
+{
+       list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
+}
+
+static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
+{
+       list_del_rcu(&wb->bdi_node);
+}
+
 #endif /* CONFIG_CGROUP_WRITEBACK */
 
 int bdi_init(struct backing_dev_info *bdi)
@@ -810,8 +833,6 @@ int bdi_init(struct backing_dev_info *bdi)
 
        ret = cgwb_bdi_init(bdi);
 
-       list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
-
        return ret;
 }
 EXPORT_SYMBOL(bdi_init);
@@ -847,6 +868,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
        if (IS_ERR(dev))
                return PTR_ERR(dev);
 
+       cgwb_bdi_register(bdi);
        bdi->dev = dev;
 
        bdi_debug_register(bdi, dev_name(dev));