From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 15 Aug 2001 14:03:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 15 Aug 2001 14:02:54 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:62205 "EHLO hermes.mvista.com") by vger.kernel.org with ESMTP id convert rfc822-to-8bit; Wed, 15 Aug 2001 14:02:48 -0400 Message-ID: <3B7AB93D.F8B5B455@mvista.com> Date: Wed, 15 Aug 2001 11:02:37 -0700 From: george anzinger Organization: Monta Vista Software X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.2.12-20b i686) X-Accept-Language: en MIME-Version: 1.0 To: Bruce Janson , linux-kernel@vger.kernel.org Subject: Re: ptrace(), fork(), sleep(), exit(), SIGCHLD In-Reply-To: <20010813093116Z270036-761+611@vger.kernel.org> <20010814092849.E13892@pc8.lineo.fr> <20010814201825Z270798-760+1687@vger.kernel.org> <3B7A9953.744977A5@mvista.com> Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org george anzinger wrote: > > Bruce Janson wrote: > > > > In article <20010814092849.E13892@pc8.lineo.fr>, > > christophe =?iso-8859-1?Q?barb=E9?= wrote: > > .. > > >Le lun, 13 aoû 2001 10:29:32, Bruce Janson a écrit : > > .. > > >> The following program behaves incorrectly when traced: > > .. > > >Have you receive off-line answers? > > .. > > > > No, though I did receive an offline reply from someone who appeared > > to have misunderstood the post. In case it wasn't clear, the problem > > is that the above program behaves differently when traced to how it > > behaves when not traced. (I do realise that in general, under newer > > Unices, when not ignored, a SIGCHLD signal may accompany the death of > > a child.) > > > > >I guess that it's certainly more a strace issue and that it's perhaps > > .. > > > > It's not clear to me whether it is a kernel, glibc or strace bug, but > > it does appear to be a bug. > > I don't have the code for usleep() handy and the man page is not much > help, but here goes: > > I think strace is using ptrace() which causes signals to be redirected > to wake up the parent (strace in this case). In particular, blocked > signals are no longer blocked. What this means is that a.) SIG CHILD is > posted, b.) the signal, not being blocked, the child is wakened, c.) > ptrace returns to the parent, d) the parent does what ever and tells the > kernel (ptrace) to continue the child with the original mask, e.) the > signal code returns 0 with out delivering the signal to the child. > Looks good, right? Wrong! The wake up at (b) pulls the child out of > the timer queue so when signal returns, the sleep (I assume nano sleep > is actually used here) call returns with the remaining sleep time as a > value. > > This is an issue for debugging also (same ptrace...). The fix is to fix > nano_sleep to match the standard which says it should only return on a > signal if the signal is delivered to the program (i.e. not on internal > "do nothing" signals). Signal in the kernel returns 1 if it calls the > task and 0 otherwise, thus nano sleep might be changed as follows: > > expire = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec); > > current->state = TASK_INTERRUPTIBLE; > - expire = schedule_timeout(expire); > + while (expire = schedule_timeout(expire) && !signal()); Still not quite right. regs needs to be dummied up (see sys_sigpause) and then: + while (expire = schedule_timeout(expire) && !do_signal(regs, NULL)); > > if (expire) { > if (rmtp) { > jiffies_to_timespec(expire, &t); > if (copy_to_user(rmtp, &t, sizeof(struct timespec))) > return -EFAULT; > } > return -EINTR; > } > return 0; > > This code is in ../kernel/timer.c > > Note that this assumes that nano_sleep() underlies usleep(). If > setitimer (via sleep() or otherwise) is used, the problem and fix is in > the library. In that case, the code needs to notice that it was > awakened but the alarm handler was not called. Still, with out the full > spec on usleep() it is not clear what it should do. > > In any case, this is a bug in nano_sleep(), where the spec is clear on > this point. > > George > - > 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/