Re: [PATCH V2] sched: Prevent balance_push() on remote runqueues

[Peter Zijlstra]

On Sat, Aug 28, 2021 at 03:55:52PM +0200, Thomas Gleixner wrote:
> sched_setscheduler() and rt_mutex_setprio() invoke the run-queue balance
> callback after changing priorities or the scheduling class of a task. The
> run-queue for which the callback is invoked can be local or remote.
> 
> That's not a problem for the regular rq::push_work which is serialized with
> a busy flag in the run-queue struct, but for the balance_push() work which
> is only valid to be invoked on the outgoing CPU that's wrong. It not only
> triggers the debug warning, but also leaves the per CPU variable push_work
> unprotected, which can result in double enqueues on the stop machine list.
> 
> Remove the warning and validate that the function is invoked on the
> outgoing CPU.
> 
> Fixes: ae7927023243 ("sched: Optimize finish_lock_switch()")
> Reported-by: Sebastian Siewior <bigeasy@xxxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Thanks!