block: flush all throttled bios when deleting the cgroup

When a process migrates to another cgroup and the original cgroup is deleted,
the restrictions of throttled bios cannot be removed. If the restrictions
are set too low, it will take a long time to complete these bios.

Refer to the process of deleting a disk to remove the restrictions and
issue bios when deleting the cgroup.

This makes difference on the behavior of throttled bios:
Before: the limit of the throttled bios can't be changed and the bios will
complete under this limit;
Now: the limit will be canceled and the throttled bios will be flushed
immediately.

References:
[1] https://lore.kernel.org/r/20220318130144.1066064-4-ming.lei@redhat.com
[2] https://lore.kernel.org/all/da861d63-58c6-3ca0-2535-9089993e9e28@huaweicloud.com/

Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20240817071108.1919729-1-lilingfeng@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 443d1f47c2ce97da7e0d794acad6ac4fdffb1179..82dbaefcfa3bf56f0079ef2e043bbc55e320e4af 100644 (file)
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1526,6 +1526,42 @@ static void throtl_shutdown_wq(struct request_queue *q)
        cancel_work_sync(&td->dispatch_work);
 }
 
+static void tg_flush_bios(struct throtl_grp *tg)
+{
+       struct throtl_service_queue *sq = &tg->service_queue;
+
+       if (tg->flags & THROTL_TG_CANCELING)
+               return;
+       /*
+        * Set the flag to make sure throtl_pending_timer_fn() won't
+        * stop until all throttled bios are dispatched.
+        */
+       tg->flags |= THROTL_TG_CANCELING;
+
+       /*
+        * Do not dispatch cgroup without THROTL_TG_PENDING or cgroup
+        * will be inserted to service queue without THROTL_TG_PENDING
+        * set in tg_update_disptime below. Then IO dispatched from
+        * child in tg_dispatch_one_bio will trigger double insertion
+        * and corrupt the tree.
+        */
+       if (!(tg->flags & THROTL_TG_PENDING))
+               return;
+
+       /*
+        * Update disptime after setting the above flag to make sure
+        * throtl_select_dispatch() won't exit without dispatching.
+        */
+       tg_update_disptime(tg);
+
+       throtl_schedule_pending_timer(sq, jiffies + 1);
+}
+
+static void throtl_pd_offline(struct blkg_policy_data *pd)
+{
+       tg_flush_bios(pd_to_tg(pd));
+}
+
 struct blkcg_policy blkcg_policy_throtl = {
        .dfl_cftypes            = throtl_files,
        .legacy_cftypes         = throtl_legacy_files,
@@ -1533,6 +1569,7 @@ struct blkcg_policy blkcg_policy_throtl = {
        .pd_alloc_fn            = throtl_pd_alloc,
        .pd_init_fn             = throtl_pd_init,
        .pd_online_fn           = throtl_pd_online,
+       .pd_offline_fn          = throtl_pd_offline,
        .pd_free_fn             = throtl_pd_free,
 };
 
@@ -1553,32 +1590,15 @@ void blk_throtl_cancel_bios(struct gendisk *disk)
         */
        rcu_read_lock();
        blkg_for_each_descendant_post(blkg, pos_css, q->root_blkg) {
-               struct throtl_grp *tg = blkg_to_tg(blkg);
-               struct throtl_service_queue *sq = &tg->service_queue;
-
-               /*
-                * Set the flag to make sure throtl_pending_timer_fn() won't
-                * stop until all throttled bios are dispatched.
-                */
-               tg->flags |= THROTL_TG_CANCELING;
-
                /*
-                * Do not dispatch cgroup without THROTL_TG_PENDING or cgroup
-                * will be inserted to service queue without THROTL_TG_PENDING
-                * set in tg_update_disptime below. Then IO dispatched from
-                * child in tg_dispatch_one_bio will trigger double insertion
-                * and corrupt the tree.
+                * disk_release will call pd_offline_fn to cancel bios.
+                * However, disk_release can't be called if someone get
+                * the refcount of device and issued bios which are
+                * inflight after del_gendisk.
+                * Cancel bios here to ensure no bios are inflight after
+                * del_gendisk.
                 */
-               if (!(tg->flags & THROTL_TG_PENDING))
-                       continue;
-
-               /*
-                * Update disptime after setting the above flag to make sure
-                * throtl_select_dispatch() won't exit without dispatching.
-                */
-               tg_update_disptime(tg);
-
-               throtl_schedule_pending_timer(sq, jiffies + 1);
+               tg_flush_bios(blkg_to_tg(blkg));
        }
        rcu_read_unlock();
        spin_unlock_irq(&q->queue_lock);