From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752590AbbJTHP6 (ORCPT ); Tue, 20 Oct 2015 03:15:58 -0400 Received: from mail-io0-f169.google.com ([209.85.223.169]:35397 "EHLO mail-io0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751643AbbJTHP4 (ORCPT ); Tue, 20 Oct 2015 03:15:56 -0400 Date: Tue, 20 Oct 2015 15:15:32 +0800 From: Boqun Feng To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Peter Zijlstra , Ingo Molnar , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Thomas Gleixner , Will Deacon , Waiman Long , Davidlohr Bueso , stable@vger.kernel.org Subject: Re: [PATCH tip/locking/core v4 1/6] powerpc: atomic: Make *xchg and *cmpxchg a full barrier Message-ID: <20151020071532.GB17714@fixme-laptop.cn.ibm.com> References: <1444838161-17209-1-git-send-email-boqun.feng@gmail.com> <1444838161-17209-2-git-send-email-boqun.feng@gmail.com> <20151014201916.GB3910@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="KFztAG8eRSV9hGtP" Content-Disposition: inline In-Reply-To: <20151014201916.GB3910@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --KFztAG8eRSV9hGtP Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Oct 14, 2015 at 01:19:17PM -0700, Paul E. McKenney wrote: >=20 > Am I missing something here? If not, it seems to me that you need > the leading lwsync to instead be a sync. >=20 > Of course, if I am not missing something, then this applies also to the > value-returning RMW atomic operations that you pulled this pattern from. > If so, it would seem that I didn't think through all the possibilities > back when PPC_ATOMIC_EXIT_BARRIER moved to sync... In fact, I believe > that I worried about the RMW atomic operation acting as a barrier, > but not as the load/store itself. :-/ >=20 Paul, I know this may be difficult, but could you recall why the __futex_atomic_op() and futex_atomic_cmpxchg_inatomic() also got involved into the movement of PPC_ATOMIC_EXIT_BARRIER to "sync"? I did some search, but couldn't find the discussion of that patch. I ask this because I recall Peter once bought up a discussion: https://lkml.org/lkml/2015/8/26/596 Peter's conclusion seems to be that we could(though didn't want to) live with futex atomics not being full barriers. Peter, just be clear, I'm not in favor of relaxing futex atomics. But if I make PPC_ATOMIC_ENTRY_BARRIER being "sync", it will also strengthen the futex atomics, just wonder whether such strengthen is a -fix- or not, considering that I want this patch to go to -stable tree. Of course, in the meanwhile of waiting for your answer, I will try to figure out this by myself ;-) Regards, Boqun --KFztAG8eRSV9hGtP Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAABCAAGBQJWJeoQAAoJEEl56MO1B/q49RsH/jQvYe8mK6e8u1Wb5wgNIw+e 57MbdqPsSpFEaopknDe7ZqHCGI9pyv1u29kfIpFLYiRkNj8hYKOpyILmcpSqMw57 NZzKgAxs/9M3K7oLWNnw1jl14emDu/uT3kw9aZfEH/Z4JeAnhq1JK45F/aj+NcwC AgsEJt9pNyWMOyWuGirWp6PK0fnhZrxfAeI3MLJV3Qj/b+Fykt2pqqKOT7YVEAJl QVMEBcJczfRlWrPLZnmYSDAIaZsHdA1/n5yD3RmK07L1NWN1BzZ9YBVupBIOVg1i WqcocQYyVkLCLu6rVvUGWZ62Xk3eLFGpGfAnj6iYAICz6NfQqiHrpN/7+jdlfLw= =UI8A -----END PGP SIGNATURE----- --KFztAG8eRSV9hGtP--