Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire

Andrea Parri
2018-07-12T08:34:55Z

> All the discussion here[1] for example is about having ordering and
> doing an smp_cond_load_acquire() on a variable which is sometimes
> protected by a CPU's rq->lock and sometimes not? Isn't that one of the
> key use cases for this whole discussion?

Not a "pure" one:

http://lkml.kernel.org/r/1530629639-27767-1-git-send-email-andrea.parri@amarulasolutions.com

we also need "W->R ordering" in schedule()! so there better be an
smp_mb__after_spinlock() or a barrier providing similar ordering.

Nick was suggesting a "weaker version" of this barrier back in:

362a61ad61199e ("fix SMP data race in pagetable setup vs walking")

c.f., the comment in mm/memory.c:__pte_alloc(), but that does not
math our pattern (UNLOCK+LOCK), AFAICT.

Andrea

>
> [1] https://lkml.org/lkml/2015/10/6/805
>
> Dan