Re: [PATCH 2/7] xen: sched: fix locking for insert_vcpu() in credit1 and RTDS

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 08/10/15 13:52, Dario Faggioli wrote:
> The insert_vcpu scheduler hook is called with an inconsistent
> locking strategy. In fact, it is sometimes invoked while
> holding the runqueue lock and sometimes when that is not the
> case.
>
> For instance, in case of schedule_cpu_switch() the lock is
> acquired in generic code. On the other hand, in case of
> sched_move_domain(), locking is left as a responsibility
> of the schedulers implementing the hook.
>
> This results in Credit1 and RTDS schedulers ending up (in
> case of sched_move_domain()) doing runqueue manipulation
> without holding any runqueue lock, which is a bug. (Credit2
> was doing the locking by itself already.)
>
> The right thing is to defer locking to the specific schedulers,
> as it's them that know what, how and when it is best to lock
> (as in: runqueue locks, vs. private scheduler locks, vs. both,
> etc.).
>
> This patch, therefore:
>  - removes any locking around insert_vcpu() from generic
>    code;
>  - add proper locking in the hook implementations, for
>    both Credit1 and RTDS.
>
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>