From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/8586 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH 1/2] pthread: add missing memory barrier Date: Mon, 28 Sep 2015 18:21:21 -0400 Message-ID: <20150928222121.GA11656@brightrain.aerifal.cx> References: <1443477525-24743-1-git-send-email-koorogi@koorogi.info> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1443478898 23129 80.91.229.3 (28 Sep 2015 22:21:38 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 28 Sep 2015 22:21:38 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-8598-gllmg-musl=m.gmane.org@lists.openwall.com Tue Sep 29 00:21:37 2015 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1Zggng-0008Re-RA for gllmg-musl@m.gmane.org; Tue, 29 Sep 2015 00:21:36 +0200 Original-Received: (qmail 12232 invoked by uid 550); 28 Sep 2015 22:21:35 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 12192 invoked from network); 28 Sep 2015 22:21:34 -0000 Content-Disposition: inline In-Reply-To: <1443477525-24743-1-git-send-email-koorogi@koorogi.info> User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:8586 Archived-At: On Mon, Sep 28, 2015 at 04:58:44PM -0500, Bobby Bingham wrote: > posix requires pthread_join to synchronize memory on success. in the > case that we call __timedwait_cp, we can rely on its futex_wake call > to synchronize memory, but we need a memory barrier for the case where > we don't call it. > --- > src/thread/pthread_join.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/src/thread/pthread_join.c b/src/thread/pthread_join.c > index 966b4ab..eb78e2f 100644 > --- a/src/thread/pthread_join.c > +++ b/src/thread/pthread_join.c > @@ -11,7 +11,9 @@ int __pthread_join(pthread_t t, void **res) > __pthread_testcancel(); > __pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs); > if (cs == PTHREAD_CANCEL_ENABLE) __pthread_setcancelstate(cs, 0); > - while ((tmp = t->tid)) __timedwait_cp(&t->tid, tmp, 0, 0, 0); > + if (!(tmp = t->tid)) a_barrier(); > + else do __timedwait_cp(&t->tid, tmp, 0, 0, 0); > + while ((tmp = t->tid)); > __pthread_setcancelstate(cs, 0); > if (res) *res = t->result; > if (t->map_base) __munmap(t->map_base, t->map_size); > -- I think this works, but it depends on __timedwait_cp containing a barrier. Is this something we should view as part of its contract or as an implementation detail? We could punt on the question and just put an unconditional a_barrier() after the loop above, but I'd kind of like to think through the question while we're looking at it. Rich