From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758175AbZBMJrp (ORCPT ); Fri, 13 Feb 2009 04:47:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751417AbZBMJrf (ORCPT ); Fri, 13 Feb 2009 04:47:35 -0500 Received: from mx2.redhat.com ([66.187.237.31]:37736 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750985AbZBMJrd (ORCPT ); Fri, 13 Feb 2009 04:47:33 -0500 Date: Fri, 13 Feb 2009 10:44:49 +0100 From: Oleg Nesterov To: Andrew Morton Cc: Denys Vlasenko , "Eric W. Biederman" , Jan Kratochvil , Kaz Kylheku , Michael Kerrisk , Roland McGrath , Ulrich Drepper , linux-kernel@vger.kernel.org Subject: [PATCH] do_wait: fix waiting for the group stop with the dead leader Message-ID: <20090213094449.GA20257@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 do_wait(WSTOPPED) assumes that p->state must be == TASK_STOPPED, this is not true if the leader is already dead. Check SIGNAL_STOP_STOPPED instead and use signal->group_exit_code. Trivial test-case: void *tfunc(void *arg) { pause(); return NULL; } int main(void) { pthread_t thr; pthread_create(&thr, NULL, tfunc, NULL); pthread_exit(NULL); return 0; } It doesn't react to ^Z (and then to ^C or ^\). The task is stopped, but bash can't see this. The bug is very old, and it was reported multiple times. This patch was sent more than a year ago (http://marc.info/?t=119713920000003) but it was ignored. >>From my pov this change also fixes other oddities (but not all) in this area. For example, before this patch: $ sleep 100 ^Z [1]+ Stopped sleep 100 $ strace -p `pidof sleep` Process 11442 attached - interrupt to quit strace hangs in do_wait(), because ->exit_code was already consumed by bash. After this patch, strace happily proceeds: --- SIGTSTP (Stopped) @ 0 (0) --- restart_syscall(<... resuming interrupted call ...> To me, this looks much more "natural" and correct. Another example. Let's suppose we have the main thread M and sub-thread T, the process is stopped, and its parent did wait(WSTOPPED). Now we can ptrace T but not M. This looks at least strange to me. Imho, do_wait() should not confuse the per-thread ptrace stops with the per-process job control stops. Signed-off-by: Oleg Nesterov --- 6.29-rc3/kernel/exit.c~WSTOPPED 2009-02-11 21:25:35.000000000 +0100 +++ 6.29-rc3/kernel/exit.c 2009-02-13 07:04:12.000000000 +0100 @@ -1345,6 +1345,18 @@ static int wait_task_zombie(struct task_ return retval; } +static int *task_stopped_code(struct task_struct *p, bool ptrace) +{ + if (ptrace) { + if (task_is_stopped_or_traced(p)) + return &p->exit_code; + } else { + if (p->signal->flags & SIGNAL_STOP_STOPPED) + return &p->signal->group_exit_code; + } + return NULL; +} + /* * Handle sys_wait4 work for one task in state TASK_STOPPED. We hold * read_lock(&tasklist_lock) on entry. If we return zero, we still hold @@ -1355,7 +1367,7 @@ static int wait_task_stopped(int ptrace, int options, struct siginfo __user *infop, int __user *stat_addr, struct rusage __user *ru) { - int retval, exit_code, why; + int retval, exit_code, *p_code, why; uid_t uid = 0; /* unneeded, required by compiler */ pid_t pid; @@ -1365,22 +1377,16 @@ static int wait_task_stopped(int ptrace, exit_code = 0; spin_lock_irq(&p->sighand->siglock); - if (unlikely(!task_is_stopped_or_traced(p))) - goto unlock_sig; - - if (!ptrace && p->signal->group_stop_count > 0) - /* - * A group stop is in progress and this is the group leader. - * We won't report until all threads have stopped. - */ + p_code = task_stopped_code(p, ptrace); + if (unlikely(!p_code)) goto unlock_sig; - exit_code = p->exit_code; + exit_code = *p_code; if (!exit_code) goto unlock_sig; if (!unlikely(options & WNOWAIT)) - p->exit_code = 0; + *p_code = 0; /* don't need the RCU readlock here as we're holding a spinlock */ uid = __task_cred(p)->uid; @@ -1536,7 +1542,7 @@ static int wait_consider_task(struct tas */ *notask_error = 0; - if (task_is_stopped_or_traced(p)) + if (task_stopped_code(p, ptrace)) return wait_task_stopped(ptrace, p, options, infop, stat_addr, ru);