From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 23213 invoked by alias); 9 Jan 2015 12:03:25 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 23193 invoked by uid 89); 9 Jan 2015 12:03:24 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.0 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Fri, 09 Jan 2015 12:03:23 +0000 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t09C3Lii021719 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Fri, 9 Jan 2015 07:03:21 -0500 Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.ams2.redhat.com [10.39.146.11]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t09C3KrH020007 for ; Fri, 9 Jan 2015 07:03:21 -0500 Message-ID: <54AFC388.7050706@redhat.com> Date: Fri, 09 Jan 2015 12:03:00 -0000 From: Pedro Alves User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: gdb-patches@sourceware.org Subject: Re: [PATCH 0/5] GNU/Linux, fix attach races/problems References: <1418748834-27545-1-git-send-email-palves@redhat.com> In-Reply-To: <1418748834-27545-1-git-send-email-palves@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-SW-Source: 2015-01/txt/msg00215.txt.bz2 On 12/16/2014 04:53 PM, Pedro Alves wrote: > Investigating an "attach" bug seemingly caused by a race, related to > the fact that on Linux we have to attach to each thread individually, > I decided to write a test that stresses that aspect of attach. The > test constantly spawns short-lived threads, and has GDB attach, debug > a little, detach, attach, rinse/repeat a few times. > > That actually exposed a set of issues, both in GDB and in > glibc/libthread_db. > > One is that the test defeats the current heuristics in place: we still > fail to attach to some threads sometimes, if the program spawns them > quickly enough. This is fixed by fetching the list of LWPs to attach > to from /proc instead of relying on libthread_db for that. > > Another is that some times we'd try to attach to a bogus lwp with > PID==-1, and do a dangerous waitpid, potentially eating an event by > mistake and breaking the debug session as result. > > Yet another is a nasty libthread_db event reporting mechanism race > related to detaching from the inferior just while a thread is > reporting an event, resulting in a subsequent attach session tripping > on broken libthread_db events. We work around this by no longer using > libthread_db for thread event creation/death reporting, which is good > on its own, for being much more robust and efficient. > > I've filed a couple glibc bugs as result of all this: > > Bug 17705 - nptl_db: stale thread create/death events if debugger detaches > https://sourceware.org/bugzilla/show_bug.cgi?id=17705 > > Bug 17707 - nptl_db: terminated and joined threads > https://sourceware.org/bugzilla/show_bug.cgi?id=17707 > > The series fixes the GDB issues and at the same time works around the > glibc issues. > > Tested on x86_64 Fedora 20, native and gdbserver. > > Comments? I've pushed this in now. Thanks, Pedro Alves