RE: [PATCH-for-4.17] xen/sched: fix race in RTDS scheduler

[Henry Wang <Henry.Wang@xxxxxxx>]

Hi Juergen,

> -----Original Message-----
> From: Juergen Gross <jgross@xxxxxxxx>
> Subject: [PATCH-for-4.17] xen/sched: fix race in RTDS scheduler
> 
> When a domain gets paused the unit runnable state can change to "not
> runnable" without the scheduling lock being involved. This means that
> a specific scheduler isn't involved in this change of runnable state.
> 
> In the RTDS scheduler this can result in an inconsistency in case a
> unit is losing its "runnable" capability while the RTDS scheduler's
> scheduling function is active. RTDS will remove the unit from the run
> queue, but doesn't do so for the replenish queue, leading to hitting
> an ASSERT() in replq_insert() later when the domain is unpaused again.
> 
> Fix that by removing the unit from the replenish queue as well in this
> case.
> 
> Fixes: 7c7b407e7772 ("xen/sched: introduce unit_runnable_state()")
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Thanks for the quick fix.

Release-acked-by: Henry Wang <Henry.Wang@xxxxxxx>

Kind regards,
Henry

> ---
>  xen/common/sched/rt.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/xen/common/sched/rt.c b/xen/common/sched/rt.c
> index d6de25531b..960a8033e2 100644
> --- a/xen/common/sched/rt.c
> +++ b/xen/common/sched/rt.c
> @@ -1087,6 +1087,7 @@ rt_schedule(const struct scheduler *ops, struct
> sched_unit *currunit,
>          else if ( !unit_runnable_state(snext->unit) )
>          {
>              q_remove(snext);
> +            replq_remove(ops, snext);
>              snext = rt_unit(sched_idle_unit(sched_cpu));
>          }
> 
> --
> 2.35.3