To restore zombie's we will create the a task, that, on its turn to run, calls do_exit(). Unlike normal tasks that exit, we need to prevent notification side effects that send signals to other processes, e.g. parent (SIGCHLD) or child tasks (per child's request). There are three main cases for such notifications: 1) do_notify_parent(): parent of a process is notified about a change in status (e.g. become zombie, reparent, etc). If parent ignores, then mark child for immediate release (skip zombie). 2) kill_orphan_pgrp(): a process group that becomes orphaned will signal stopped jobs (HUP then CONT). 3) forget_original_parent(): children of a process are signaled (per request) with p->pdeath_signal Remember that restoring signal state (for any restarting task) must complete _before_ it is allowed to resume execution, and not during the resume. Otherwise, a running task may send a signal to another task that hasn't restored yet, so the new signal will be lost soon-after. I considered two possible way to address this: 1. Add another sync point to restart: all tasks will first restore their state without signals (all signals blocked), and zombies call do_exit(). A sync point then will ensure that all zombies are gone and their effects done. Then all tasks restore their signal state (and mask), and sync (new point) again. Only then they may resume execution. The main disadvantage is the added complexity and inefficiency, for no good reason. 2. Introduce PF_RESTARTING: mark all restarting tasks with a new flag, and teach the above three notifications to skip sending the signal if theis flag is set. The main advantage is simplicity and completeness. Also, such a flag may to be useful later on. This the method implemented. Changelog [ckpt-v19-rc3]: - Rebase to kernel 2.6.33 Changelog [ckpt-v19-rc1]: - In reparent_thread() test for PF_RESTARTING on parent Signed-off-by: Oren Laadan <orenl@xxxxxxxxxxxxxxx> Acked-by: Serge E. Hallyn <serue@xxxxxxxxxx> Tested-by: Serge E. Hallyn <serue@xxxxxxxxxx> --- kernel/exit.c | 6 +++++- kernel/signal.c | 4 ++++ 2 files changed, 9 insertions(+), 1 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index f8eb8bb..576576a 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -300,6 +300,10 @@ kill_orphaned_pgrp(struct task_struct *tsk, struct task_struct *parent) struct pid *pgrp = task_pgrp(tsk); struct task_struct *ignored_task = tsk; + /* restarting zombie doesn't trigger signals */ + if (tsk->flags & PF_RESTARTING) + return; + if (!parent) /* exit: our father is in a different pgrp than * we are and we were the only connection outside. @@ -785,7 +789,7 @@ static void forget_original_parent(struct task_struct *father) BUG_ON(task_ptrace(t)); t->parent = t->real_parent; } - if (t->pdeath_signal) + if (t->pdeath_signal && !(t->flags & PF_RESTARTING)) group_send_sig_info(t->pdeath_signal, SEND_SIG_NOINFO, t); } while_each_thread(p, t); diff --git a/kernel/signal.c b/kernel/signal.c index 934ae5e..ce8d404 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1432,6 +1432,10 @@ int do_notify_parent(struct task_struct *tsk, int sig) BUG_ON(!task_ptrace(tsk) && (tsk->group_leader != tsk || !thread_group_empty(tsk))); + /* restarting zombie doesn't notify parent */ + if (tsk->flags & PF_RESTARTING) + return ret; + info.si_signo = sig; info.si_errno = 0; /* -- 1.6.3.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>