Re: [BUG] srcu: false-positive WARN in cleanup_srcu_struct() after 78a38cbf6f20

["Zqiang" <qiang.zhang@linux.dev>]

> 
> On 8/25/26 21:33, Zqiang wrote:
> 
> > 
> > If srcu_barrier() be invoke before srcu_cleanup(), and after srcu_barrier()
> >  completion, there are no concurrent srcu grace period start again (e.g. call_srcu() calls),
> >  the timer_delete_sync() should return false, the rcu_segcblist_n_cbs()
> >  will not be check.
> >  Or did I miss something?
> > 
> In srcu_gp_end(), delayed work timer is always armed in SRCU_SIZE_SMALL mode regardless of whether its cblist has callbacks:

In this SRCU_SIZE_SMALL mode, when queue delayed work timer, the cblist is always no-empty.
unless invoke start_poll_synchronize_srcu() to begin SRCU garce period, 
otherwise invoke call_srcu() or synchronize_srcu*() will insert callback.

Thanks
Zqiang

> 
>  if (ss_state < SRCU_SIZE_WAIT_BARRIER) {
>  srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, get_boot_cpu_id()),
>  cbdelay);
>  } else {
>  ...
>  }
> 
> and with cbdelay=1 (the non-expedited path) srcu_schedule_cbs_sdp() arms the per-CPU delay_work timer for the next jiffy. This includes the srcu_gp_end() whose grace period makes the barrier's callbacks ready, so an armed timer is left pending when srcu_invoke_callbacks() completes the barrier.
> 
> Thanks
> Sunho Park
>