The patch titled pid_ns: (BUG 11391) change ->child_reaper when init->group_leader exits has been added to the -mm tree. Its filename is pid_ns-bug-11391-change-child_reaper-when-init-group_leader-exits.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: pid_ns: (BUG 11391) change ->child_reaper when init->group_leader exits From: Oleg Nesterov <oleg@xxxxxxxxxx> We don't change pid_ns->child_reaper when the main thread of the subnamespace init exits. As Robert Rex <robert.rex@xxxxxxxxxx> pointed out this is wrong. 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. Addresses http://bugzilla.kernel.org/show_bug.cgi?id=11391 Reported-by: Robert Rex <robert.rex@xxxxxxxxxx> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Acked-by: Serge Hallyn <serue@xxxxxxxxxx> Acked-by: Pavel Emelyanov <xemul@xxxxxxxxxx> Acked-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/exit.c | 78 +++++++++++++++++---------------------- kernel/pid_namespace.c | 6 --- 2 files changed, 34 insertions(+), 50 deletions(-) diff -puN kernel/exit.c~pid_ns-bug-11391-change-child_reaper-when-init-group_leader-exits kernel/exit.c --- a/kernel/exit.c~pid_ns-bug-11391-change-child_reaper-when-init-group_leader-exits +++ a/kernel/exit.c @@ -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); } diff -puN kernel/pid_namespace.c~pid_ns-bug-11391-change-child_reaper-when-init-group_leader-exits kernel/pid_namespace.c --- a/kernel/pid_namespace.c~pid_ns-bug-11391-change-child_reaper-when-init-group_leader-exits +++ a/kernel/pid_namespace.c @@ -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; } _ Patches currently in -mm which might be from oleg@xxxxxxxxxx are exit-signals-use-of-uninitialized-field-notify_count.patch pid_ns-zap_pid_ns_processes-fix-the-child_reaper-changing.patch pid_ns-bug-11391-change-child_reaper-when-init-group_leader-exits.patch linux-next.patch posix-timers-dont-switch-to-group_leader-if-it_process-dies.patch posix-timers-always-do-get_task_structtimer-it_process.patch posix-timers-sys_timer_create-remove-the-buggy-pf_exiting-check.patch posix-timers-sys_timer_create-simplify-and-s-tasklist-rcu.patch posix-timers-move-the-initialization-of-timer-sigq-from-send-to-create-path.patch posix-timers-sys_timer_create-cleanup-the-error-handling.patch posix-timers-kill-it_sigev_signo-and-it_sigev_value.patch posix-timers-lock_timer-kill-the-bogus-it_id-check.patch posix-timers-lock_timer-make-it-readable.patch posix-timers-use-struct-pid-instead-of-struct-task_struct.patch posix-timers-check-it_signal-instead-of-it_pid-to-validate-the-timer.patch posix-timers-simplify-de_thread-exit_itimers-path.patch make-ptrace_untrace-static.patch coredump-format_corename-dont-append-%pid-if-multi-threaded.patch kthread_bind-use-wait_task_inactivetask_uninterruptible.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html