From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-5.5 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 895E41FF40 for ; Thu, 1 Dec 2016 00:04:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755213AbcLAAEl (ORCPT ); Wed, 30 Nov 2016 19:04:41 -0500 Received: from cloud.peff.net ([104.130.231.41]:49405 "EHLO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751631AbcLAAEk (ORCPT ); Wed, 30 Nov 2016 19:04:40 -0500 Received: (qmail 27615 invoked by uid 109); 1 Dec 2016 00:04:40 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.84) with SMTP; Thu, 01 Dec 2016 00:04:40 +0000 Received: (qmail 27338 invoked by uid 111); 1 Dec 2016 00:05:15 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.84) with SMTP; Wed, 30 Nov 2016 19:05:15 -0500 Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Wed, 30 Nov 2016 19:04:38 -0500 Date: Wed, 30 Nov 2016 19:04:38 -0500 From: Jeff King To: Brandon Williams Cc: Junio C Hamano , git@vger.kernel.org Subject: Re: What's cooking in git.git (Nov 2016, #06; Mon, 28) Message-ID: <20161201000437.altjlcsn4u7rwe5c@sigill.intra.peff.net> References: <20161129010538.GA121643@google.com> <20161129063759.6mgmpqx3kbyuqjwi@sigill.intra.peff.net> <20161129065125.cwlbkctniy7oshj2@sigill.intra.peff.net> <20161130195427.GA166433@google.com> <20161130232823.GA192901@google.com> <20161130233204.ihbrjwwu3yiv4ugq@sigill.intra.peff.net> <20161130234056.iltitkszvccbjivp@sigill.intra.peff.net> <20161130234248.GB192901@google.com> <20161130234636.6az7xfywzprpn6ly@sigill.intra.peff.net> <20161130235952.4j63gkdlbobjitdb@sigill.intra.peff.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20161130235952.4j63gkdlbobjitdb@sigill.intra.peff.net> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Wed, Nov 30, 2016 at 06:59:52PM -0500, Jeff King wrote: > So I think there is some other chdir(). I'm not sure if there is an easy > way to get a backtrace on every call to chdir() in every thread. I'm > sure somebody more clever than me could figure out how to make gdb do it > automatically, but it might be workable manually. I think the chdir was > in the main thread. Ah, that turned out to be quite easy. The culprit is probably: (gdb) bt #0 chdir () at ../sysdeps/unix/syscall-template.S:84 #1 0x00005555555fe259 in real_path_internal (path=0x5555559f6b30 "su:b/../.git/modules/su:b", die_on_error=1) at abspath.c:84 #2 0x00005555555fe48a in real_path (path=0x5555559f6b30 "su:b/../.git/modules/su:b") at abspath.c:135 #3 0x00005555556d09e6 in read_gitfile_gently (path=0x5555559f6ac0 "su:b/.git", return_error_code=0x0) at setup.c:555 #4 0x00005555556d19cf in resolve_gitdir (suspect=0x5555559f6ac0 "su:b/.git") at setup.c:1021 #5 0x00005555556e7e34 in is_submodule_populated (path=0x5555559f5ec8 "su:b") at submodule.c:244 #6 0x00005555555a0f05 in grep_submodule (opt=0x7fffffffd8b0, sha1=0x0, filename=0x5555559f5ec8 "su:b", path=0x5555559f5ec8 "su:b") at builtin/grep.c:619 #7 0x00005555555a12ac in grep_cache (opt=0x7fffffffd8b0, pathspec=0x7fffffffd880, cached=0) at builtin/grep.c:700 #8 0x00005555555a36cb in cmd_grep (argc=0, argv=0x7fffffffdf40, prefix=0x0) at builtin/grep.c:1257 #9 0x000055555556603b in run_builtin (p=0x5555559b3ad8 , argc=4, argv=0x7fffffffdf40) at git.c:373 #10 0x00005555555662bc in handle_builtin (argc=4, argv=0x7fffffffdf40) at git.c:572 #11 0x000055555556641a in run_argv (argcp=0x7fffffffddfc, argv=0x7fffffffddf0) at git.c:630 #12 0x00005555555665a8 in cmd_main (argc=4, argv=0x7fffffffdf40) at git.c:702 #13 0x00005555555fde47 in main (argc=7, argv=0x7fffffffdf28) at common-main.c:40 So is_submodule_populated() needs to take a lock. But what's really gross is that the _other_ threads need to lock just to call lstat(). Presumably it could be done as a reader/writer type of lock where many "reader" threads can take the "I need to lstat()" lock simultaneously, but block when an "I'm going to chdir()" writer holds it. -Peff