bdi: Shutdown writeback on all cgwbs in cgwb_bdi_destroy()

BugLink: http://bugs.launchpad.net/bugs/1659111
Currently we waited for all cgwbs to get freed in cgwb_bdi_destroy()
which also means that writeback has been shutdown on them. Since this
wait is going away, directly shutdown writeback on cgwbs from
cgwb_bdi_destroy() to avoid live writeback structures after
bdi_unregister() has finished. To make that safe with concurrent
shutdown from cgwb_release_workfn(), we also have to make sure
wb_shutdown() returns only after the bdi_writeback structure is really
shutdown.

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 5318ce7d46866e1dbc20ab9349b93753edba0b3e)
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/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 5f218afa52005bcc5dc40489619162875bdd6e28..68a3c84a5dc36283bcec27a46fc10a72a64a4179 100644 (file)
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -21,6 +21,7 @@ struct dentry;
  */
 enum wb_state {
        WB_registered,          /* bdi_register() was done */
+       WB_shutting_down,       /* wb_shutdown() in progress */
        WB_writeback_running,   /* Writeback is in progress */
        WB_has_dirty_io,        /* Dirty inodes on ->b_{dirty|io|more_io} */
 };

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index b809899e92294befa30e4fce53bf4f06be98ee06..f6c9ca40ce9ce84c2b6146bc1ade4030501a9c6d 100644 (file)
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -355,8 +355,15 @@ static void wb_shutdown(struct bdi_writeback *wb)
        spin_lock_bh(&wb->work_lock);
        if (!test_and_clear_bit(WB_registered, &wb->state)) {
                spin_unlock_bh(&wb->work_lock);
+               /*
+                * Wait for wb shutdown to finish if someone else is just
+                * running wb_shutdown(). Otherwise we could proceed to wb /
+                * bdi destruction before wb_shutdown() is finished.
+                */
+               wait_on_bit(&wb->state, WB_shutting_down, TASK_UNINTERRUPTIBLE);
                return;
        }
+       set_bit(WB_shutting_down, &wb->state);
        spin_unlock_bh(&wb->work_lock);
 
        cgwb_remove_from_bdi_list(wb);
@@ -368,6 +375,12 @@ static void wb_shutdown(struct bdi_writeback *wb)
        mod_delayed_work(bdi_wq, &wb->dwork, 0);
        flush_delayed_work(&wb->dwork);
        WARN_ON(!list_empty(&wb->work_list));
+       /*
+        * Make sure bit gets cleared after shutdown is finished. Matches with
+        * the barrier provided by test_and_clear_bit() above.
+        */
+       smp_wmb();
+       clear_bit(WB_shutting_down, &wb->state);
 }
 
 static void wb_exit(struct bdi_writeback *wb)
@@ -698,12 +711,21 @@ static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
 {
        struct radix_tree_iter iter;
        void **slot;
+       struct bdi_writeback *wb;
 
        WARN_ON(test_bit(WB_registered, &bdi->wb.state));
 
        spin_lock_irq(&cgwb_lock);
        radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
                cgwb_kill(*slot);
+
+       while (!list_empty(&bdi->wb_list)) {
+               wb = list_first_entry(&bdi->wb_list, struct bdi_writeback,
+                                     bdi_node);
+               spin_unlock_irq(&cgwb_lock);
+               wb_shutdown(wb);
+               spin_lock_irq(&cgwb_lock);
+       }
        spin_unlock_irq(&cgwb_lock);
 
        /*