Date: Wed, 23 Aug 2023 05:38:06 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Jessica Clarke <jrtc27@freebsd.org> Cc: "src-committers@freebsd.org" <src-committers@freebsd.org>, "dev-commits-src-all@freebsd.org" <dev-commits-src-all@freebsd.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@freebsd.org> Subject: Re: git: 4a69fc16a583 - main - Add membarrier(2) Message-ID: <ZOVxDqInEgUhBaIN@kib.kiev.ua> In-Reply-To: <748B7A01-5011-44EE-BB04-282AE96F9B5B@freebsd.org> References: <202308230007.37N07cOK082906@gitrepo.freebsd.org> <748B7A01-5011-44EE-BB04-282AE96F9B5B@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Aug 23, 2023 at 02:18:12AM +0100, Jessica Clarke wrote: > On 23 Aug 2023, at 01:07, Konstantin Belousov <kib@FreeBSD.org> wrote: > > > > The branch main has been updated by kib: > > > > URL: https://cgit.FreeBSD.org/src/commit/?id=4a69fc16a583face922319c476f3e739d9ce9140 > > > > commit 4a69fc16a583face922319c476f3e739d9ce9140 > > Author: Konstantin Belousov <kib@FreeBSD.org> > > AuthorDate: 2021-10-07 21:10:07 +0000 > > Commit: Konstantin Belousov <kib@FreeBSD.org> > > CommitDate: 2023-08-23 00:02:21 +0000 > > > > Add membarrier(2) > > > > This is an attempt at clean-room implementation of the Linux' > > membarrier(2) syscall. For documentation, you would need to read > > both membarrier(2) Linux man page, the comments in Linux > > kernel/sched/membarrier.c implementation and possibly look at > > actual uses. > > > > Sponsored by: The FreeBSD Foundation > > MFC after: 1 week > > Differential revision: https://reviews.freebsd.org/D32360 > > --- > > ... > > diff --git a/sys/sys/membarrier.h b/sys/sys/membarrier.h > > new file mode 100644 > > index 000000000000..958b769da23e > > --- /dev/null > > +++ b/sys/sys/membarrier.h > > @@ -0,0 +1,70 @@ > > +/*- > > + * Copyright (c) 2021 The FreeBSD Foundation > > + * > > + * This software were developed by Konstantin Belousov <kib@FreeBSD.org> > > + * under sponsorship from the FreeBSD Foundation. > > + * > > + * Redistribution and use in source and binary forms, with or without > > + * modification, are permitted provided that the following conditions > > + * are met: > > + * 1. Redistributions of source code must retain the above copyright > > + * notice, this list of conditions and the following disclaimer. > > + * 2. Redistributions in binary form must reproduce the above copyright > > + * notice, this list of conditions and the following disclaimer in the > > + * documentation and/or other materials provided with the distribution. > > + * > > + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND > > + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE > > + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE > > + * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE > > + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL > > + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS > > + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) > > + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT > > + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY > > + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF > > + * SUCH DAMAGE. > > + */ > > + > > +#ifndef __SYS_MEMBARRIER_H__ > > +#define __SYS_MEMBARRIER_H__ > > + > > +#include <sys/cdefs.h> > > + > > +/* > > + * The enum membarrier_cmd values are bits. The MEMBARRIER_CMD_QUERY > > + * command returns a bitset indicating which commands are supported. > > + * Also the value of MEMBARRIER_CMD_QUERY is zero, so it is > > + * effectively not returned by the query. > > + */ > > +enum membarrier_cmd { > > + MEMBARRIER_CMD_QUERY = 0x00000000, > > + MEMBARRIER_CMD_GLOBAL = 0x00000001, > > + MEMBARRIER_CMD_SHARED = MEMBARRIER_CMD_GLOBAL, > > + MEMBARRIER_CMD_GLOBAL_EXPEDITED = 0x00000002, > > + MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED = 0x00000004, > > + MEMBARRIER_CMD_PRIVATE_EXPEDITED = 0x00000008, > > + MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = 0x00000010, > > + MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE = 0x00000020, > > + MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE = 0x00000040, > > + > > + /* > > + * RSEQ constants are defined for source compatibility but are > > + * not yes supported, MEMBARRIER_CMD_QUERY does not return > > + * them in the mask. > > + */ > > + MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ = 0x00000080, > > + MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ = 0x00000100, > > Or we could not define them. membarrier(2) came into Linux in 4.3, but > these two are only since 5.10. Defining something we may or may not > ever implement that code should have compatibility for anyway seems > like a bad idea. Or should we provide all of the Linux UAPI to FreeBSD > processes with ENOSYS stubs? Clearly not. So why is this special? IMO > these should not be added unless we have an rseq implementation, which > has itself received several objections on the review. The added _RSEQ bits behave according to the membarrier(2) specification, they are defined but not returned in the mask of supported operations. I found that have all of them defined makes compiling some program easier, AFAIR. > > I also don’t see why this is suddenly being landed now without warning. > There’s been no activity by you on the review since just over a year > ago. And landing new syscalls days before the 14 branch point doesn’t > seem like great practice to me... Would I know that reviewers did not act for a year, I committed the patch a year ago. The addition does not change any existing code path in the kernel.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?ZOVxDqInEgUhBaIN>