Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761013AbXE1HIZ (ORCPT ); Mon, 28 May 2007 03:08:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755315AbXE1HIS (ORCPT ); Mon, 28 May 2007 03:08:18 -0400 Received: from mail.screens.ru ([213.234.233.54]:39516 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751866AbXE1HIS (ORCPT ); Mon, 28 May 2007 03:08:18 -0400 Date: Mon, 28 May 2007 11:07:53 +0400 From: Oleg Nesterov To: Satoru Takeuchi Cc: Alan Cox , Andrew Morton , "Eric W. Biederman" , Ingo Molnar , Roland McGrath , linux-kernel@vger.kernel.org Subject: Re: [BUG] signal: multithread program returns with wrong errno on receiving SIGSTOP Message-ID: <20070528070753.GA989@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2050 Lines: 71 Satoru Takeuchi wrote: > > I found a bug on signal subsystem. If there is some multithread program > and one of the thread is blocking on the system call, it returns with > wrong errno on receiving SIGSTOP and following SIGCONT. It doesn't matter in this particular case, but in general it is good to report the kernel version as well. > 1. issue the test program (attached on this mail) from term A. > > $ ./mt-wrong-errno > > 2. send SIGSTOP to test program from term B. > > $ ps a > ... > 9685 pts/3 Sl+ 0:00 ./mt-wrong-errno > 9688 pts/4 R+ 0:00 ps a > $ kill -STOP 9685 > > 3. send SIGCONT to test program from term B. > > $ kill -CONT 9685 > > Expected Result > =============== > > `./mt-wrong-errno' restarts read syscall (and stop again by receiving > SIGTTIN). > > Actual Result > ============= > > `./mt-wrong-errno' returns with wrong errno 512 means ERESTARTSYS. > The comment on include/linux/errno.h says "this errno should never be > seen by user program." So it's definitely a bug. Wild guess, drivers/char/n_tty.c:job_control() kill_pgrp(task_pgrp(current), SIGTTIN, 1); return -ERESTARTSYS; This is wrong. kill_pgrp()->__group_send_sig_info() sends SIGTTIN to the thread group, but can choose any sub-thread as a target for signal_wake_up(). This means we return ERESTARTSYS, but signal_pending() != true, bug. Satoru, could you re-test with the untested patch below? Oleg. --- t/drivers/char/n_tty.c~ 2007-04-05 12:18:26.000000000 +0400 +++ t/drivers/char/n_tty.c 2007-05-28 10:57:58.000000000 +0400 @@ -1191,6 +1191,7 @@ static int job_control(struct tty_struct is_current_pgrp_orphaned()) return -EIO; kill_pgrp(task_pgrp(current), SIGTTIN, 1); + set_thread_flag(TIF_SIGPENDING); return -ERESTARTSYS; } } - 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/