Oleg Nesterov wrote:
On 07/26, Pavel Emelyanov wrote:
@@ -895,6 +915,7 @@ fastcall NORET_TYPE void do_exit(long co
{
struct task_struct *tsk = current;
int group_dead;
+ struct pid_namespace *pid_ns = tsk->nsproxy->pid_ns;
profile_task_exit(tsk);
@@ -905,9 +926,10 @@ fastcall NORET_TYPE void do_exit(long co
if (unlikely(!tsk->pid))
panic("Attempted to kill the idle task!");
if (unlikely(tsk == task_child_reaper(tsk))) {
- if (task_active_pid_ns(tsk) != &init_pid_ns)
- task_active_pid_ns(tsk)->child_reaper =
- init_pid_ns.child_reaper;
+ if (pid_ns != &init_pid_ns) {
+ zap_pid_ns_processes(pid_ns);
+ pid_ns->child_reaper = init_pid_ns.child_reaper;
+ }
else
panic("Attempted to kill init!");
No, no, this is wrong. Yes, the current code is buggy too, I'll send
the fix.
I think this code should be moved below under the "if (group_dead)",
and we should use tsk->group_leader.
+void zap_pid_ns_processes(struct pid_namespace *pid_ns)
+{
+ int i;
+ int nr;
+ int nfree;
+ int options = WNOHANG|WEXITED|__WALL;
+
+repeat:
+ /*
+ * We know pid == 1 is terminating. Find remaining pid_ts
+ * in the namespace, signal them and then wait for them
+ * exit.
+ */
+ nr = next_pidmap(pid_ns, 1);
+ while (nr > 0) {
+ kill_proc_info(SIGKILL, SEND_SIG_PRIV, nr);
+ nr = next_pidmap(pid_ns, nr);
+ }
+
+ nr = next_pidmap(pid_ns, 1);
+ while (nr > 0) {
+ do_wait(nr, options, NULL, NULL, NULL);
When the first child of init exits, it sends SIGCHLD. After that,
do_wait() will never sleep, so we are doing a busy-wait loop.
Not good, especially when we have a niced child, can livelock.
+ nr = next_pidmap(pid_ns, nr);
+ }
+
+ nfree = 0;
+ for (i = 0; i < PIDMAP_ENTRIES; i++)
+ nfree += atomic_read(&pid_ns->pidmap[i].nr_free);
+
+ /*
+ * If pidmap has entries for processes other than 0 and 1, retry.
+ */
+ if (nfree < (BITS_PER_PAGE * PIDMAP_ENTRIES - 2))
+ goto repeat;
This doesn't look right.
Suppose that some "struct pid" was pinned from the parent namespace.
In that case zap_pid_ns_processes() will burn CPU until put_pid(), bad.
Nope. struct pid can be pinned, but the pidmap "fingerprint" cannot.
So as soon as the release_task() is called the pidmap becomes free and
we can proceed.
However I agree with the "burn CPU" issue - wait must sleep if needed.
I think we can rely on forget_original_child() and do something like
this:
zap_active_ns_processes(void)
{
// kill all tasks in our ns and below
kill(-1, SIGKILL);
That would be too slow to walk through all the tasks in a node searching
for a couple of them we need. fing_ge_pid() looks better to me.
do {
clear_thread_flag(TIF_SIGPENDING);
} while (wait(NULL) != -ECHLD);
}
Oleg.
Thanks,
Pavel
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