Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753798AbYH0CYT (ORCPT ); Tue, 26 Aug 2008 22:24:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751877AbYH0CYH (ORCPT ); Tue, 26 Aug 2008 22:24:07 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:55223 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751003AbYH0CYE (ORCPT ); Tue, 26 Aug 2008 22:24:04 -0400 Date: Tue, 26 Aug 2008 21:24:03 -0500 From: "Serge E. Hallyn" To: Oleg Nesterov Cc: Andrew Morton , "Eric W. Biederman" , Pavel Emelyanov , Robert Rex , Roland McGrath , Sukadev Bhattiprolu , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/4] pid_ns: (BUG 11391) change ->child_reaper when init->group_leader exits Message-ID: <20080827022403.GA2320@us.ibm.com> References: <20080824154912.GA3780@tv-sign.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080824154912.GA3780@tv-sign.ru> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6277 Lines: 170 Quoting Oleg Nesterov (oleg@tv-sign.ru): > We don't change pid_ns->child_reaper when the main thread of the > subnamespace init exits. As Robert Rex > pointed out this is wrong. I think there was another way that could go wrong as well - if the main thread exited but sighand had another user, then the child_reaper would not be changed, zap_pid_ns_processes() would not be called, and children would continue to run and at death try to signal the dead main thread. > Yes, the re-parenting itself works correctly, but if the reparented > task exits it needs ->parent->nsproxy->pid_ns in do_notify_parent(), > and if the main thread is zombie its ->nsproxy was already cleared > by exit_task_namespaces(). > > Introduce the new function, find_new_reaper(), which finds the new > ->parent for the re-parenting and changes ->child_reaper if needed. > Kill the now unneeded exit_child_reaper(). > > Also move the changing of ->child_reaper from zap_pid_ns_processes() > to find_new_reaper(), this consolidates the games with ->child_reaper > and makes it stable under tasklist_lock. > > Reported-by: Robert Rex > Signed-off-by: Oleg Nesterov Sat on this for a bit - the only thing about this that worried me was that zap_pid_ns_processes() is moved much further down in do_exit(). After looking I see no reason why that would be a problem, though. Acked-by: Serge Hallyn Thanks, Oleg. > > kernel/pid_namespace.c | 6 --- > kernel/exit.c | 78 +++++++++++++++++++++---------------------------- > 2 files changed, 34 insertions(+), 50 deletions(-) > > --- 2.6.27-rc4/kernel/pid_namespace.c~2_SWITCH_REAPER 2008-08-24 17:22:59.000000000 +0400 > +++ 2.6.27-rc4/kernel/pid_namespace.c 2008-08-24 18:22:44.000000000 +0400 > @@ -179,12 +179,6 @@ void zap_pid_ns_processes(struct pid_nam > rc = sys_wait4(-1, NULL, __WALL, NULL); > } while (rc != -ECHILD); > > - /* > - * We can not clear ->child_reaper or leave it alone. > - * There may by stealth EXIT_DEAD tasks on ->children, > - * forget_original_parent() must move them somewhere. > - */ > - pid_ns->child_reaper = init_pid_ns.child_reaper; > acct_exit_ns(pid_ns); > return; > } > --- 2.6.27-rc4/kernel/exit.c~2_SWITCH_REAPER 2008-08-24 16:46:51.000000000 +0400 > +++ 2.6.27-rc4/kernel/exit.c 2008-08-24 18:22:37.000000000 +0400 > @@ -831,26 +831,50 @@ static void reparent_thread(struct task_ > * the child reaper process (ie "init") in our pid > * space. > */ > +static struct task_struct *find_new_reaper(struct task_struct *father) > +{ > + struct pid_namespace *pid_ns = task_active_pid_ns(father); > + struct task_struct *thread; > + > + thread = father; > + while_each_thread(father, thread) { > + if (thread->flags & PF_EXITING) > + continue; > + if (unlikely(pid_ns->child_reaper == father)) > + pid_ns->child_reaper = thread; > + return thread; > + } > + > + if (unlikely(pid_ns->child_reaper == father)) { > + write_unlock_irq(&tasklist_lock); > + if (unlikely(pid_ns == &init_pid_ns)) > + panic("Attempted to kill init!"); > + > + zap_pid_ns_processes(pid_ns); > + write_lock_irq(&tasklist_lock); > + /* > + * We can not clear ->child_reaper or leave it alone. > + * There may by stealth EXIT_DEAD tasks on ->children, > + * forget_original_parent() must move them somewhere. > + */ > + pid_ns->child_reaper = init_pid_ns.child_reaper; > + } > + > + return pid_ns->child_reaper; > +} > + > static void forget_original_parent(struct task_struct *father) > { > - struct task_struct *p, *n, *reaper = father; > + struct task_struct *p, *n, *reaper; > LIST_HEAD(ptrace_dead); > > write_lock_irq(&tasklist_lock); > - > + reaper = find_new_reaper(father); > /* > * First clean up ptrace if we were using it. > */ > ptrace_exit(father, &ptrace_dead); > > - do { > - reaper = next_thread(reaper); > - if (reaper == father) { > - reaper = task_child_reaper(father); > - break; > - } > - } while (reaper->flags & PF_EXITING); > - > list_for_each_entry_safe(p, n, &father->children, sibling) { > p->real_parent = reaper; > if (p->parent == father) { > @@ -959,39 +983,6 @@ static void check_stack_usage(void) > static inline void check_stack_usage(void) {} > #endif > > -static inline void exit_child_reaper(struct task_struct *tsk) > -{ > - if (likely(tsk->group_leader != task_child_reaper(tsk))) > - return; > - > - if (tsk->nsproxy->pid_ns == &init_pid_ns) > - panic("Attempted to kill init!"); > - > - /* > - * @tsk is the last thread in the 'cgroup-init' and is exiting. > - * Terminate all remaining processes in the namespace and reap them > - * before exiting @tsk. > - * > - * Note that @tsk (last thread of cgroup-init) may not necessarily > - * be the child-reaper (i.e main thread of cgroup-init) of the > - * namespace i.e the child_reaper may have already exited. > - * > - * Even after a child_reaper exits, we let it inherit orphaned children, > - * because, pid_ns->child_reaper remains valid as long as there is > - * at least one living sub-thread in the cgroup init. > - > - * This living sub-thread of the cgroup-init will be notified when > - * a child inherited by the 'child-reaper' exits (do_notify_parent() > - * uses __group_send_sig_info()). Further, when reaping child processes, > - * do_wait() iterates over children of all living sub threads. > - > - * i.e even though 'child_reaper' thread is listed as the parent of the > - * orphaned children, any living sub-thread in the cgroup-init can > - * perform the role of the child_reaper. > - */ > - zap_pid_ns_processes(tsk->nsproxy->pid_ns); > -} > - > NORET_TYPE void do_exit(long code) > { > struct task_struct *tsk = current; > @@ -1051,7 +1042,6 @@ NORET_TYPE void do_exit(long code) > } > group_dead = atomic_dec_and_test(&tsk->signal->live); > if (group_dead) { > - exit_child_reaper(tsk); > hrtimer_cancel(&tsk->signal->real_timer); > exit_itimers(tsk->signal); > } -- 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/