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Date:   Thu, 12 Jul 2018 10:34:44 +0200
From:   Andrea Parri <>
To:     Daniel Lustig <>
Cc:     Peter Zijlstra <>,
        Will Deacon <>,
        Alan Stern <>,
        "Paul E. McKenney" <>,
        LKMM Maintainers -- Akira Yokosawa <>,
        Boqun Feng <>,
        David Howells <>,
        Jade Alglave <>,
        Luc Maranget <>,
        Nicholas Piggin <>,
        Kernel development list <>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and
 remove it for ordinary release/acquire

> 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:

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.


> [1]
> Dan

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