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Date: Fri, 31 Aug 2018 20:28:46 +0200 From: Andrea Parri <andrea.parri@...rulasolutions.com> To: Will Deacon <will.deacon@....com> Cc: Alan Stern <stern@...land.harvard.edu>, Andrea Parri <parri.andrea@...il.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, mingo@...nel.org, peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr, akiyks@...il.com Subject: Re: [PATCH RFC LKMM 1/7] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire > > Yes, it's true that implementing locks with atomic_cmpxchg_acquire > > should be correct on all existing architectures. And Paul has invited > > a patch to modify the LKMM accordingly. If you feel that such a change > > would be a useful enhancement to the LKMM's applicability, please write > > it. > > Yes, please! That would be the "RmW" discussion which Andrea partially > quoted earlier on, so getting that going independently from this patch > sounds like a great idea to me. That was indeed one of the proposal we discussed. As you recalled, that proposal only covered RmWs load-acquire (and ordinary store-release); in particular, I realized that comments such as: "The atomic_cond_read_acquire() call above has provided the necessary acquire semantics required for locking." [from kernel/locking/qspinlock.c] (for example) would still _not have "generic validity" _if we added the above po-unlock-rf-lock-po term... (which, again, makes me somehow uncon- fortable); Would to have _all_ the acquire be admissible for you? Andrea > > Cheers, > > Will
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