tree b9703358195945550846d0e59259178cf5274d83
parent 640f17c82460e9724fd256f0a1f5d99e7ff0bda4
author Peter Zijlstra <peterz@infradead.org> 1611151541 +0100
committer Peter Zijlstra <peterz@infradead.org> 1611324583 +0100

sched: Prepare to use balance_push in ttwu()

In preparation of using the balance_push state in ttwu() we need it to
provide a reliable and consistent state.

The immediate problem is that rq->balance_callback gets cleared every
schedule() and then re-set in the balance_push_callback() itself. This
is not a reliable signal, so add a variable that stays set during the
entire time.

Also move setting it before the synchronize_rcu() in
sched_cpu_deactivate(), such that we get guaranteed visibility to
ttwu(), which is a preempt-disable region.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210121103506.966069627@infradead.org