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SubjectRe: [PATCH v2 04/19] sched: Prepare for Core-wide rq->lock
On Sat, May 08, 2021 at 04:07:35PM +0800, Aubrey Li wrote:
> > +#ifdef CONFIG_SMP
> > +/*
> > + * double_rq_lock - safely lock two runqueues
> > + */
> > +void double_rq_lock(struct rq *rq1, struct rq *rq2)
>
> Do we need the static lock checking here?
> __acquires(rq1->lock)
> __acquires(rq2->lock)
>
> > +{
> > + lockdep_assert_irqs_disabled();
> > +
> > + if (rq_order_less(rq2, rq1))
> > + swap(rq1, rq2);
> > +
> > + raw_spin_rq_lock(rq1);
> > + if (rq_lockp(rq1) == rq_lockp(rq2)) {
>
> And here?
> __acquire(rq2->lock);
>
> > + return;
> }
> > +
> > + raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);
> > +}
> > +#endif

I'd as soon rip out all that sparse annotation crud; I don't think I've
ever had any benefit from it.


> > @@ -2368,11 +2354,11 @@ static inline void double_rq_unlock(stru
> > __releases(rq1->lock)
> > __releases(rq2->lock)
> > {
> > - raw_spin_rq_unlock(rq1);
> > if (rq_lockp(rq1) != rq_lockp(rq2))
> > raw_spin_rq_unlock(rq2);
> > else
> > __release(rq2->lock);
> > + raw_spin_rq_unlock(rq1);
>
> This change seems not necessary, as the softlockup root cause is not
> the misorder lock release.

No, it really is needed; rq_lockp() is not stable if we don't hold a
lock.

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