Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751022Ab1BNRxd (ORCPT ); Mon, 14 Feb 2011 12:53:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:5216 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750757Ab1BNRxb (ORCPT ); Mon, 14 Feb 2011 12:53:31 -0500 Date: Mon, 14 Feb 2011 18:45:03 +0100 From: Oleg Nesterov To: Tejun Heo Cc: Denys Vlasenko , Roland McGrath , jan.kratochvil@redhat.com, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE_ATTACH Message-ID: <20110214174503.GB15847@redhat.com> References: <20110204105343.GA12133@htj.dyndns.org> <20110207174821.GA1237@redhat.com> <20110209141803.GH3770@htj.dyndns.org> <201102132325.55353.vda.linux@googlemail.com> <20110214151340.GP18742@htj.dyndns.org> <20110214173012.GA18742@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20110214173012.GA18742@htj.dyndns.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2029 Lines: 47 On 02/14, Tejun Heo wrote: > > On Mon, Feb 14, 2011 at 06:20:52PM +0100, Denys Vlasenko wrote: > > >> 23:02:15.622112 nanosleep({30, 0}, NULL) = ? ERESTART_RESTARTBLOCK (To be restarted) > > >> 23:02:23.781165 --- SIGSTOP (Stopped (signal)) @ 0 (0) --- > > >> 23:02:23.781251 --- SIGSTOP (Stopped (signal)) @ 0 (0) --- > > >> ? ? (I forgot again why we see it twice. Another quirk I guess...) > > >> 23:02:23.781310 restart_syscall(<... resuming interrupted call ...>) = 0 > > >> 23:02:45.622433 close(1) ? ? ? ? ? ? ? ?= 0 > > >> 23:02:45.622743 close(2) ? ? ? ? ? ? ? ?= 0 > > >> 23:02:45.622885 exit_group(0) ? ? ? ? ? = ? > ... > > > This can be fixed by updating strace, right? ?strace can look at the > > > wait(2) exit code and if the tracee stopped for group stop, wait for > > > the tracee to be continued instead of issuing PTRACE_SYSCALL. > > > > But tracee didn't stop _yet_. Signal is not delivered _yet_, debugger > > can decide at this point whether to deliver it: > > ptrace(PTRACE_SYSCALL, $PID, 0x1, SIGSTOP) > > or ignore: > > ptrace(PTRACE_SYSCALL, $PID, 0x1, 0) > > > > strace has to deliver SIGSTOP if it wants to make program run exactly > > as it would run without strace. So it tries to do so. > > Currently, ptrace machinery doesn't react as strace, its user, expects it to. > > Okay, maybe I'm missing something but so once SIGSTOP is determined to > be delivered, then the tracee enters group stop and that's the second > SIGSTOP notification you get. Yes, this is correct. But my head spins ;) I have already lost the picture. > At that point, strace should wait for > the tracee to be continued by SIGCONT. That should work, right? Again, given that strace is the real parent, in this particular case I think strace can work as you suggest. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/