blk-iocost: do not WARN if iocg was already offlined

In iocg_pay_debt(), warn is triggered if 'active_list' is empty, which
is intended to confirm iocg is active when it has debt. However, warn
can be triggered during a blkcg or disk removal, if iocg_waitq_timer_fn()
is run at that time:

  WARNING: CPU: 0 PID: 2344971 at block/blk-iocost.c:1402 iocg_pay_debt+0x14c/0x190
  Call trace:
  iocg_pay_debt+0x14c/0x190
  iocg_kick_waitq+0x438/0x4c0
  iocg_waitq_timer_fn+0xd8/0x130
  __run_hrtimer+0x144/0x45c
  __hrtimer_run_queues+0x16c/0x244
  hrtimer_interrupt+0x2cc/0x7b0

The warn in this situation is meaningless. Since this iocg is being
removed, the state of the 'active_list' is irrelevant, and 'waitq_timer'
is canceled after removing 'active_list' in ioc_pd_free(), which ensures
iocg is freed after iocg_waitq_timer_fn() returns.

Therefore, add the check if iocg was already offlined to avoid warn
when removing a blkcg or disk.

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20240419093257.3004211-1-linan666@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index baa20c8..690ca99 100644 (file)
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1439,8 +1439,11 @@ static void iocg_pay_debt(struct ioc_gq *iocg, u64 abs_vpay,
        lockdep_assert_held(&iocg->ioc->lock);
        lockdep_assert_held(&iocg->waitq.lock);
 
-       /* make sure that nobody messed with @iocg */
-       WARN_ON_ONCE(list_empty(&iocg->active_list));
+       /*
+        * make sure that nobody messed with @iocg. Check iocg->pd.online
+        * to avoid warn when removing blkcg or disk.
+        */
+       WARN_ON_ONCE(list_empty(&iocg->active_list) && iocg->pd.online);
        WARN_ON_ONCE(iocg->inuse > 1);
 
        iocg->abs_vdebt -= min(abs_vpay, iocg->abs_vdebt);