Messages in this thread | | | Date | Tue, 3 Jul 2018 19:07:57 +0200 | From | Andrea Parri <> | Subject | Re: [PATCH v3 2/3] locking: Clarify requirements for smp_mb__after_spinlock() |
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On Tue, Jul 03, 2018 at 08:39:10AM -0700, Paul E. McKenney wrote:
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> > + * smp_mb__after_spinlock() provides the equivalent of a full memory barrier > > + * between program-order earlier lock acquisitions and program-order later > > Not just the earlier lock acquisition, but also all program-order earlier > memory accesses, correct?
I understand: "but also all program-order earlier memory accesses program-order before that lock acquisition(s) ...". Yes, but:
- I considered this as implied by the above (L ->mb M2 and M1 ->po L implies M1 ->mb M2, where M1, M2 are memory accesses and L is a lock acquisition);
- my prose abilities are limited ;-), and I was/am unable to come up with an (to me) acceptable or readable enough way to make it explicit; some ideas?
> > + * WRITE_ONCE(X, 1); WRITE_ONCE(Y, 1); > > + * spin_lock(S); smp_mb(); > > + * smp_mb__after_spinlock(); r1 = READ_ONCE(X); > > + * r0 = READ_ONCE(Y); > > + * spin_unlock(S); > > Should we say that this is an instance of the SB pattern? (Am OK either > way, just asking the question.)
I don't think we *should* ;-), but I'm also OK either way.
Andrea
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