Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752289Ab1BNSOX (ORCPT ); Mon, 14 Feb 2011 13:14:23 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34245 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752131Ab1BNSOT (ORCPT ); Mon, 14 Feb 2011 13:14:19 -0500 Date: Mon, 14 Feb 2011 19:06:09 +0100 From: Oleg Nesterov To: Denys Vlasenko Cc: Tejun Heo , 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: <20110214180609.GE15847@redhat.com> References: <20110204105343.GA12133@htj.dyndns.org> <20110207174821.GA1237@redhat.com> <20110209141803.GH3770@htj.dyndns.org> <201102132325.55353.vda.linux@googlemail.com> <20110214153149.GB8761@redhat.com> <20110214173910.GA15847@redhat.com> <20110214180034.GD15847@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20110214180034.GD15847@redhat.com> 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: 1860 Lines: 47 On 02/14, Oleg Nesterov wrote: > > On 02/14, Denys Vlasenko wrote: > > > > On Mon, Feb 14, 2011 at 6:39 PM, Oleg Nesterov wrote: > > > On 02/14, Denys Vlasenko wrote: > > >> > > >> On Mon, Feb 14, 2011 at 4:31 PM, Oleg Nesterov wrote: > > >> > On 02/13, Denys Vlasenko wrote: > > >> >> > > >> >> $ strace -tt sleep 30 > > >> >> 23:02:15.619262 execve("/bin/sleep", ["sleep", "30"], [/* 30 vars */]) = 0 > > >> >> ... > > >> >> 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...) > > >> > > > >> > ? ? ?(this is correct, the tracee reports the signal=SIGSTOP, then > > >> > ? ? ? it reports it actually stopps with exit_code=SIGSTOP) > > >> > > >> Ah, I see. Is there any way debugger can distinguish between these two > > >> different stops? > > > > > > IIRC, the (only?) way to distinguish is to check last_siginfo != NULL > > > via ptrace(PTRACE_GETSIGINFO). > > > > What do you think strace needs to do when it sees second SIGSTOP > > (meaning "in theory", not "on current kernel which may be buggy")? > > > > ptrace(PTRACE_SYSCALL, $PID, 0x1, 0)? > > proably this, or even ptrace(PTRACE_SYSCALL, $PID, 0x1, SIGSTOP). > I think. > > (assuming that ptrace_resume() respects TASK_STOPPED) Oh, but I forgot to mention... there is another problem, _any_ ptrace request when the tracee is stopped turns it into TASK_TRACED. 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/