From owner-svn-src-head@freebsd.org Sun Oct 8 08:33:14 2017 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 52993E2DDED; Sun, 8 Oct 2017 08:33:14 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4E6A167B2F; Sun, 8 Oct 2017 08:33:12 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id v988X7uS019017 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sun, 8 Oct 2017 11:33:07 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua v988X7uS019017 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id v988X7Ux019015; Sun, 8 Oct 2017 11:33:07 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sun, 8 Oct 2017 11:33:07 +0300 From: Konstantin Belousov To: Don Lewis Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r324313 - head/sys/amd64/amd64 Message-ID: <20171008083307.GG95911@kib.kiev.ua> References: <20171007201142.GE95911@kib.kiev.ua> <201710072054.v97Ks5nX062548@gw.catspoiler.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201710072054.v97Ks5nX062548@gw.catspoiler.org> User-Agent: Mutt/1.9.1 (2017-09-22) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 08 Oct 2017 08:33:14 -0000 On Sat, Oct 07, 2017 at 01:54:05PM -0700, Don Lewis wrote: > On 7 Oct, Konstantin Belousov wrote: > > On Sat, Oct 07, 2017 at 01:04:09PM -0700, Don Lewis wrote: > >> On 5 Oct, Konstantin Belousov wrote: > >> > Author: kib > >> > Date: Thu Oct 5 12:50:03 2017 > >> > New Revision: 324313 > >> > URL: https://svnweb.freebsd.org/changeset/base/324313 > >> > > >> > Log: > >> > Avoid a race betweem freeing LDT and context switches. > >> > > >> > cpu_switch.S uses curproc->p_md.md_ldt value as the flag indicating > >> > presence of the process LDT. The flag is checked and then ldt segment > >> > descriptor is copied into the CPU' GDT slot. > >> > > >> > Disallow context switches around clearing of the curproc LDT state by > >> > performing the cleanup in critical section. Ensure that the md_ldt > >> > flag is cleared before md_ldt_sd descriptor content is destroyed by > >> > inserting fence between the operations. > >> > > >> > We depend on the x86 memory model strong ordering guarantees, in > >> > particular, that cpu_switch.S observes the writes to md_ldt and > >> > md_ldt_sd in the expected order. > >> > >> I don't know which of this series of commits is responsible, but I think > >> that it fixed the build of lang/ghc on Ryzen. > >> > >> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=221029#c102 > > > > Does ghc use LDT on amd64 ? This sounds unbelievable. > > I have no idea, but ghc would reliably fail to build on my Ryzen machine > up through r323398, and at r324367 it seems to reliably build. Could you try to bisect ? I reviewed all kernel changes and do not see anything which could be marked as possible fix for whatever kernel issue causing usermode fault.