From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755581AbZGATbn (ORCPT ); Wed, 1 Jul 2009 15:31:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755821AbZGATb1 (ORCPT ); Wed, 1 Jul 2009 15:31:27 -0400 Received: from mx2.redhat.com ([66.187.237.31]:56827 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756072AbZGATb0 (ORCPT ); Wed, 1 Jul 2009 15:31:26 -0400 Date: Wed, 1 Jul 2009 21:28:44 +0200 From: Oleg Nesterov To: Andrew Morton Cc: Roland McGrath , Vitaly Mayatskikh , linux-kernel@vger.kernel.org Subject: [PATCH 1/1] ptrace: __ptrace_detach: do __wake_up_parent() if we reap the tracee Message-ID: <20090701192844.GA26624@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 The bug is old, it wasn't cause by recent changes. Test case: static void *tfunc(void *arg) { int pid = (long)arg; assert(ptrace(PTRACE_ATTACH, pid, NULL, NULL) == 0); kill(pid, SIGKILL); sleep(1); return NULL; } int main(void) { pthread_t th; long pid = fork(); if (!pid) pause(); signal(SIGCHLD, SIG_IGN); assert(pthread_create(&th, NULL, tfunc, (void*)pid) == 0); int r = waitpid(-1, NULL, __WNOTHREAD); printf("waitpid: %d %m\n", r); return 0; } Before the patch this program hangs, after this patch waitpid() correctly fails with errno == -ECHILD. The problem is, __ptrace_detach() reaps the EXIT_ZOMBIE tracee if its ->real_parent is our sub-thread and we ignore SIGCHLD. But in this case we should wake up other threads which can sleep in do_wait(). Signed-off-by: Oleg Nesterov --- include/linux/sched.h | 1 + kernel/signal.c | 9 --------- kernel/exit.c | 5 +++++ kernel/ptrace.c | 11 +++++++---- 4 files changed, 13 insertions(+), 13 deletions(-) --- WAIT/include/linux/sched.h~PT_DETACH_WAKE_PARENT 2009-06-19 01:12:47.000000000 +0200 +++ WAIT/include/linux/sched.h 2009-07-01 20:20:57.000000000 +0200 @@ -1951,6 +1951,7 @@ extern int kill_pgrp(struct pid *pid, in extern int kill_pid(struct pid *pid, int sig, int priv); extern int kill_proc_info(int, struct siginfo *, pid_t); extern int do_notify_parent(struct task_struct *, int); +extern void __wake_up_parent(struct task_struct *p, struct task_struct *parent); extern void force_sig(int, struct task_struct *); extern void force_sig_specific(int, struct task_struct *); extern int send_sig(int, struct task_struct *, int); --- WAIT/kernel/signal.c~PT_DETACH_WAKE_PARENT 2009-07-01 20:05:07.000000000 +0200 +++ WAIT/kernel/signal.c 2009-07-01 20:22:44.000000000 +0200 @@ -1383,15 +1383,6 @@ ret: } /* - * Wake up any threads in the parent blocked in wait* syscalls. - */ -static inline void __wake_up_parent(struct task_struct *p, - struct task_struct *parent) -{ - wake_up_interruptible_sync(&parent->signal->wait_chldexit); -} - -/* * Let a parent know about the death of a child. * For a stopped/continued status change, use do_notify_parent_cldstop instead. * --- WAIT/kernel/exit.c~PT_DETACH_WAKE_PARENT 2009-07-01 20:05:11.000000000 +0200 +++ WAIT/kernel/exit.c 2009-07-01 20:23:42.000000000 +0200 @@ -1563,6 +1563,11 @@ static int ptrace_do_wait(struct wait_op return 0; } +void __wake_up_parent(struct task_struct *p, struct task_struct *parent) +{ + wake_up_interruptible_sync(&parent->signal->wait_chldexit); +} + static long do_wait(struct wait_opts *wo) { DECLARE_WAITQUEUE(wait, current); --- WAIT/kernel/ptrace.c~PT_DETACH_WAKE_PARENT 2009-07-01 19:59:01.000000000 +0200 +++ WAIT/kernel/ptrace.c 2009-07-01 20:52:58.000000000 +0200 @@ -266,9 +266,10 @@ static int ignoring_children(struct sigh * or self-reaping. Do notification now if it would have happened earlier. * If it should reap itself, return true. * - * If it's our own child, there is no notification to do. - * But if our normal children self-reap, then this child - * was prevented by ptrace and we must reap it now. + * If it's our own child, there is no notification to do. But if our normal + * children self-reap, then this child was prevented by ptrace and we must + * reap it now, in that case we must also wake up sub-threads sleeping in + * do_wait(). */ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p) { @@ -278,8 +279,10 @@ static bool __ptrace_detach(struct task_ if (!task_detached(p) && thread_group_empty(p)) { if (!same_thread_group(p->real_parent, tracer)) do_notify_parent(p, p->exit_signal); - else if (ignoring_children(tracer->sighand)) + else if (ignoring_children(tracer->sighand)) { + __wake_up_parent(p, tracer); p->exit_signal = -1; + } } if (task_detached(p)) { /* Mark it as in the process of being reaped. */