From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753873Ab1GHRQf (ORCPT ); Fri, 8 Jul 2011 13:16:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11432 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751763Ab1GHRQd (ORCPT ); Fri, 8 Jul 2011 13:16:33 -0400 Date: Fri, 8 Jul 2011 19:13:54 +0200 From: Oleg Nesterov To: Tejun Heo , Linus Torvalds Cc: vda.linux@googlemail.com, jan.kratochvil@redhat.com, pedro@codesourcery.com, indan@nul.nu, bdonlan@gmail.com, linux-kernel@vger.kernel.org Subject: [PATCH 2/3] ptrace: mv send-SIGSTOP from do_fork() to ptrace_init_task() Message-ID: <20110708171354.GC26943@redhat.com> References: <20110708171320.GA26943@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110708171320.GA26943@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 If the new child is traced, do_fork() adds the pending SIGSTOP. It assumes that either it is traced because of auto-attach or the tracer attached later, in both cases sigaddset/set_thread_flag is correct even if SIGSTOP is already pending. Now that we have PTRACE_SEIZE this is no longer right in the latter case. If the tracer does PTRACE_SEIZE after copy_process() makes the child visible the queued SIGSTOP is wrong. We could check PT_SEIZED bit and change ptrace_attach() to set both PT_PTRACED and PT_SEIZED bits simultaneously but see the next patch, we need to know whether this child was auto-attached or not anyway. So this patch simply moves this code to ptrace_init_task(), this way we can never race with ptrace_attach(). Signed-off-by: Oleg Nesterov --- include/linux/ptrace.h | 3 +++ kernel/fork.c | 12 ------------ 2 files changed, 3 insertions(+), 12 deletions(-) --- ptrace/include/linux/ptrace.h~4_send_stop_from_ptrace_init 2011-07-08 17:24:46.000000000 +0200 +++ ptrace/include/linux/ptrace.h 2011-07-08 18:32:05.000000000 +0200 @@ -227,6 +227,9 @@ static inline void ptrace_init_task(stru if (unlikely(ptrace) && current->ptrace) { child->ptrace = current->ptrace; __ptrace_link(child, current->parent); + + sigaddset(&child->pending.signal, SIGSTOP); + set_tsk_thread_flag(child, TIF_SIGPENDING); } } --- ptrace/kernel/fork.c~4_send_stop_from_ptrace_init 2011-07-08 17:24:46.000000000 +0200 +++ ptrace/kernel/fork.c 2011-07-08 17:25:25.000000000 +0200 @@ -37,7 +37,6 @@ #include #include #include -#include #include #include #include @@ -1522,17 +1521,6 @@ long do_fork(unsigned long clone_flags, audit_finish_fork(p); /* - * Child is ready but hasn't started running yet. Queue - * SIGSTOP if it's gonna be ptraced - it doesn't matter who - * attached/attaching to this task, the pending SIGSTOP is - * right in any case. - */ - if (unlikely(p->ptrace)) { - sigaddset(&p->pending.signal, SIGSTOP); - set_tsk_thread_flag(p, TIF_SIGPENDING); - } - - /* * We set PF_STARTING at creation in case tracing wants to * use this to distinguish a fully live task from one that * hasn't finished SIGSTOP raising yet. Now we clear it