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@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
include/linux/backing-dev-defs.h | 1 +
mm/backing-dev.c | 22 ++++++++++++++++++++++
2 files changed, 23 insertions(+)
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 8fb3dcdebc80..8af720f22a2d 100644
--- 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 e3d56dba4da8..b67be4fc12c4 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -356,8 +356,15 @@ 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);
@@ -369,6 +376,12 @@ 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)
@@ -699,12 +712,21 @@ 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);
/*
--
2.10.2
