From: Oleg Nesterov Date: Fri, 19 Oct 2007 06:40:00 +0000 (-0700) Subject: pid namespaces: rework forget_original_parent() X-Git-Tag: v5.15~44532 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=762a24beed3f3ab93224bd447710e6c36fcf1968;p=mirror_ubuntu-kernels.git pid namespaces: rework forget_original_parent() A pid namespace is a "view" of a particular set of tasks on the system. They work in a similar way to filesystem namespaces. A file (or a process) can be accessed in multiple namespaces, but it may have a different name in each. In a filesystem, this name might be /etc/passwd in one namespace, but /chroot/etc/passwd in another. For processes, a process may have pid 1234 in one namespace, but be pid 1 in another. This allows new pid namespaces to have basically arbitrary pids, and not have to worry about what pids exist in other namespaces. This is essential for checkpoint/restart where a restarted process's pid might collide with an existing process on the system's pid. In this particular implementation, pid namespaces have a parent-child relationship, just like processes. A process in a pid namespace may see all of the processes in the same namespace, as well as all of the processes in all of the namespaces which are children of its namespace. Processes may not, however, see others which are in their parent's namespace, but not in their own. The same goes for sibling namespaces. The know issue to be solved in the nearest future is signal handling in the namespace boundary. That is, currently the namespace's init is treated like an ordinary task that can be killed from within an namespace. Ideally, the signal handling by the namespace's init should have two sides: when signaling the init from its namespace, the init should look like a real init task, i.e. receive only those signals, that is explicitly wants to; when signaling the init from one of the parent namespaces, init should look like an ordinary task, i.e. receive any signal, only taking the general permissions into account. The pid namespace was developed by Pavel Emlyanov and Sukadev Bhattiprolu and we eventually came to almost the same implementation, which differed in some details. This set is based on Pavel's patches, but it includes comments and patches that from Sukadev. Many thanks to Oleg, who reviewed the patches, pointed out many BUGs and made valuable advises on how to make this set cleaner. This patch: We have to call exit_task_namespaces() only after the exiting task has reparented all his children and is sure that no other threads will reparent theirs for it. Why this is needed is explained in appropriate patch. This one only reworks the forget_original_parent() so that after calling this a task cannot be/become parent of any other task. We check PF_EXITING instead of ->exit_state while choosing the new parent. Note that tasklits_lock acts as a barrier, everyone who takes tasklist after us (when forget_original_parent() drops it) must see PF_EXITING. The other changes are just cleanups. They just move some code from exit_notify to forget_original_parent(). It is a bit silly to declare ptrace_dead in exit_notify(), take tasklist, pass ptrace_dead to forget_original_parent(), unlock-lock-unlock tasklist, and then use ptrace_dead. Signed-off-by: Oleg Nesterov Signed-off-by: Pavel Emelyanov Cc: Sukadev Bhattiprolu Cc: Paul Menage Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/exit.c b/kernel/exit.c index 179ac74bf911..3f2182ccf187 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -666,10 +666,14 @@ reparent_thread(struct task_struct *p, struct task_struct *father, int traced) * the child reaper process (ie "init") in our pid * space. */ -static void -forget_original_parent(struct task_struct *father, struct list_head *to_release) +static void forget_original_parent(struct task_struct *father) { struct task_struct *p, *n, *reaper = father; + struct list_head ptrace_dead; + + INIT_LIST_HEAD(&ptrace_dead); + + write_lock_irq(&tasklist_lock); do { reaper = next_thread(reaper); @@ -677,7 +681,7 @@ forget_original_parent(struct task_struct *father, struct list_head *to_release) reaper = task_child_reaper(father); break; } - } while (reaper->exit_state); + } while (reaper->flags & PF_EXITING); /* * There are only two places where our children can be: @@ -714,12 +718,23 @@ forget_original_parent(struct task_struct *father, struct list_head *to_release) * while it was being traced by us, to be able to see it in wait4. */ if (unlikely(ptrace && p->exit_state == EXIT_ZOMBIE && p->exit_signal == -1)) - list_add(&p->ptrace_list, to_release); + list_add(&p->ptrace_list, &ptrace_dead); } + list_for_each_entry_safe(p, n, &father->ptrace_children, ptrace_list) { p->real_parent = reaper; reparent_thread(p, father, 1); } + + write_unlock_irq(&tasklist_lock); + BUG_ON(!list_empty(&father->children)); + BUG_ON(!list_empty(&father->ptrace_children)); + + list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_list) { + list_del_init(&p->ptrace_list); + release_task(p); + } + } /* @@ -730,7 +745,6 @@ static void exit_notify(struct task_struct *tsk) { int state; struct task_struct *t; - struct list_head ptrace_dead, *_p, *_n; struct pid *pgrp; if (signal_pending(tsk) && !(tsk->signal->flags & SIGNAL_GROUP_EXIT) @@ -751,8 +765,6 @@ static void exit_notify(struct task_struct *tsk) spin_unlock_irq(&tsk->sighand->siglock); } - write_lock_irq(&tasklist_lock); - /* * This does two things: * @@ -761,12 +773,9 @@ static void exit_notify(struct task_struct *tsk) * as a result of our exiting, and if they have any stopped * jobs, send them a SIGHUP and then a SIGCONT. (POSIX 3.2.2.2) */ + forget_original_parent(tsk); - INIT_LIST_HEAD(&ptrace_dead); - forget_original_parent(tsk, &ptrace_dead); - BUG_ON(!list_empty(&tsk->children)); - BUG_ON(!list_empty(&tsk->ptrace_children)); - + write_lock_irq(&tasklist_lock); /* * Check to see if any process groups have become orphaned * as a result of our exiting, and if they have any stopped @@ -831,12 +840,6 @@ static void exit_notify(struct task_struct *tsk) write_unlock_irq(&tasklist_lock); - list_for_each_safe(_p, _n, &ptrace_dead) { - list_del_init(_p); - t = list_entry(_p, struct task_struct, ptrace_list); - release_task(t); - } - /* If the process is dead, release it - nobody will wait for it */ if (state == EXIT_DEAD) release_task(tsk);