From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.bugs Subject: bug#36609: 27.0.50; Possible race-condition in threading implementation Date: Fri, 12 Jul 2019 21:27:40 +0300 Message-ID: <835zo72jmr.fsf@gnu.org> References: <87muhks3b5.fsf@hochschule-trier.de> <83muhj2zmb.fsf@gnu.org> <83ims72xcj.fsf@gnu.org> <83a7dj2sz9.fsf@gnu.org> Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="227292"; mail-complaints-to="usenet@blaine.gmane.org" Cc: 36609@debbugs.gnu.org, politza@hochschule-trier.de To: Pip Cet Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Fri Jul 12 20:28:08 2019 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1hm0HA-000wwj-I2 for geb-bug-gnu-emacs@m.gmane.org; Fri, 12 Jul 2019 20:28:08 +0200 Original-Received: from localhost ([::1]:51764 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hm0H7-000645-NZ for geb-bug-gnu-emacs@m.gmane.org; Fri, 12 Jul 2019 14:28:05 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:55772) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hm0H5-00063y-2t for bug-gnu-emacs@gnu.org; Fri, 12 Jul 2019 14:28:03 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hm0H4-0006qb-3u for bug-gnu-emacs@gnu.org; Fri, 12 Jul 2019 14:28:03 -0400 Original-Received: from debbugs.gnu.org ([209.51.188.43]:60127) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1hm0H3-0006o4-Ur for bug-gnu-emacs@gnu.org; Fri, 12 Jul 2019 14:28:02 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1hm0H3-0001K2-Pm for bug-gnu-emacs@gnu.org; Fri, 12 Jul 2019 14:28:01 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Eli Zaretskii Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Fri, 12 Jul 2019 18:28:01 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 36609 X-GNU-PR-Package: emacs Original-Received: via spool by 36609-submit@debbugs.gnu.org id=B36609.15629560785070 (code B ref 36609); Fri, 12 Jul 2019 18:28:01 +0000 Original-Received: (at 36609) by debbugs.gnu.org; 12 Jul 2019 18:27:58 +0000 Original-Received: from localhost ([127.0.0.1]:40715 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1hm0H0-0001Jh-2E for submit@debbugs.gnu.org; Fri, 12 Jul 2019 14:27:58 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:43414) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1hm0Gy-0001JU-MA for 36609@debbugs.gnu.org; Fri, 12 Jul 2019 14:27:57 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]:45519) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hm0Gr-0006gE-SC; Fri, 12 Jul 2019 14:27:50 -0400 Original-Received: from [176.228.60.248] (port=2709 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from ) id 1hm0Gq-0001EM-Bz; Fri, 12 Jul 2019 14:27:49 -0400 In-reply-to: (message from Pip Cet on Fri, 12 Jul 2019 18:06:29 +0000) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.51.188.43 X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.org gmane.emacs.bugs:162797 Archived-At: > From: Pip Cet > Date: Fri, 12 Jul 2019 18:06:29 +0000 > Cc: politza@hochschule-trier.de, 36609@debbugs.gnu.org > > > Then we should make sure we release it when the thread function exits, > > That's too late, it's legitimate for the thread to have a signal > handler. We need to release the lock at precisely the time that > unbind_to would release it. I had also another proposal: > > or before we call Fsignal from post_acquire_global_lock. There's no > > reason to use the unwind-protect machinery for that, I think. > > If we call Fsignal, surely the unwind-protect machinery is already set > up and we can safely call it? So unbind_to would work again... Sorry, I don't want to call unwind-protect there. Call me paranoid, if you want. > I guess I've changed my mind: the unwind-protect machinery does > precisely what we want, we should simply document that thread_select > can exit nonlocally and that the select functions need to be written > to cater to that. > > Two places call xg_select, and they both run long after unbind_to works. > > Doing this without the unwind-protect machinery is difficult: for > example, a comment in post_acquire_global_lock claims > unbind_for_thread_switch can exit nonlocally, though I don't think > that actually happens or we would have seen the bug report. > > What's your proposal for doing this? Like I said: release the lock before calling Fsignal. We could do that before calling unbind_for_thread_switch, if needed.