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handle the multi-threaded init's exit() properly 

With or without this patch, multi-threaded init's are not fully supported,
but do_exit() is completely wrong.  This becomes a real problem when we
support pid namespaces.

1. do_exit() panics when the main thread of /sbin/init exits. It should not
   until the whole thread group exits. Move the code below, under the
   "if (group_dead)" check.

   Note: this means that forget_original_parent() can use an already dead
   child_reaper()'s task_struct. This is OK for /sbin/init because

   	- do_wait() from alive sub-thread still can reap a zombie, we iterate
   	  over all sub-thread's ->children lists

   	- do_notify_parent() will wakeup some alive sub-thread because it sends
   	  the group-wide signal

   However, we should remove choose_new_parent()->BUG_ON(reaper->exit_state)
   for this.

2. We are playing games with ->nsproxy->pid_ns. This code is bogus today, and
   it has to be changed anyway when we really support pid namespaces, just
   remove it.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Roland McGrath <roland@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2007-10-16 23:26:49 -07:00 committed by Linus Torvalds
parent 8e9073ed02
commit 84eb646b6e
1 changed files with 11 additions and 20 deletions
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31
kernel/exit.c
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@ -592,17 +592,6 @@ static void exit_mm(struct task_struct * tsk)
mmput(mm);
}
static inline void
choose_new_parent(struct task_struct *p, struct task_struct *reaper)
{
/*
* Make sure we're not reparenting to ourselves and that
* the parent is not a zombie.
*/
BUG_ON(p == reaper || reaper->exit_state);
p->real_parent = reaper;
}
static void
reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
{
@ -710,7 +699,7 @@ forget_original_parent(struct task_struct *father, struct list_head *to_release)
if (father == p->real_parent) {
/* reparent with a reaper, real father it's us */
choose_new_parent(p, reaper);
p->real_parent = reaper;
reparent_thread(p, father, 0);
} else {
/* reparent ptraced task to its real parent */
@ -731,7 +720,7 @@ forget_original_parent(struct task_struct *father, struct list_head *to_release)
}
list_for_each_safe(_p, _n, &father->ptrace_children) {
p = list_entry(_p, struct task_struct, ptrace_list);
choose_new_parent(p, reaper);
p->real_parent = reaper;
reparent_thread(p, father, 1);
}
}
@ -882,6 +871,14 @@ 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 != child_reaper(tsk)))
return;
panic("Attempted to kill init!");
}
fastcall NORET_TYPE void do_exit(long code)
{
struct task_struct *tsk = current;
@ -895,13 +892,6 @@ fastcall NORET_TYPE void do_exit(long code)
panic("Aiee, killing interrupt handler!");
if (unlikely(!tsk->pid))
panic("Attempted to kill the idle task!");
if (unlikely(tsk == child_reaper(tsk))) {
if (tsk->nsproxy->pid_ns != &init_pid_ns)
tsk->nsproxy->pid_ns->child_reaper = init_pid_ns.child_reaper;
else
panic("Attempted to kill init!");
}
if (unlikely(current->ptrace & PT_TRACE_EXIT)) {
current->ptrace_message = code;
@ -951,6 +941,7 @@ fastcall 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);
}