On Thu, Nov 12, 2015 at 03:14:51PM +0800, Boqun Feng wrote: > Hmm.. probably incorrect.. because the ACQUIRE semantics of spin_lock() > only guarantees that the memory operations following spin_lock() can't > be reorder before the *LOAD* part of spin_lock() not the *STORE* part, > i.e. the case below can happen(assuming the spin_lock() is implemented > as ll/sc loop) > > spin_lock(&lock): > r1 = *lock; // LL, r1 == 0 > o = READ_ONCE(object); // could be reordered here. > *lock = 1; // SC > > This could happen because of the ACQUIRE semantics of spin_lock(), and > the current implementation of spin_lock() on PPC allows this happen.
Urgh, you just _had_ to send an email like this, didn't you ;-) I think AARGH64 does the same thing. They either use LDAXR/STXR, which also places the ACQUIRE on the load, or use LDADDA (v8.1) which I suspect does the same, but I'm not entirely sure how to decode these 8.1 atomics yet. Let me think a little more on this.. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
