On Sat, Mar 14, 2015 at 08:24:56PM +0100, Oleg Nesterov wrote:
On 03/14, Josh Triplett wrote:
quoted
On Sat, Mar 14, 2015 at 03:35:58PM +0100, Oleg Nesterov wrote:
quoted
On 03/12, Josh Triplett wrote:
quoted
@@ -598,7 +600,9 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
if (group_dead)
kill_orphaned_pgrp(tsk->group_leader, NULL);
- if (unlikely(tsk->ptrace)) {
+ if (tsk->autoreap) {
+ autoreap = true;
+ } else if (unlikely(tsk->ptrace)) {
int sig = thread_group_leader(tsk) &&
thread_group_empty(tsk) &&
!ptrace_reparented(tsk) ?@@ -612,8 +616,10 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
}
tsk->exit_state = autoreap ? EXIT_DEAD : EXIT_ZOMBIE;
- if (tsk->exit_state == EXIT_DEAD)
+ if (tsk->exit_state == EXIT_DEAD) {
list_add(&tsk->ptrace_entry, &dead);
+ clonefd_do_notify(tsk);
+ }
And even ignoring semantics issues, this change looks simply buggy anyway ;)
How can we do list_add(&tsk->ptrace_entry) if it is traced by _another_ task?
->ptrace_entry is used by debugger.
That list_add was there before; I didn't change that.
But this doesn't matter,
quoted
I just added a
second line inside the EXIT_DEAD case, to call clonefd_do_notify (which
wakes up potential callers of poll/read).
No. Please read this code before and after your patch. You also added
if (tsk->autoreap)
autoreap = true;
at the start. At this can trigger the _wrong_ list_add(&tsk->ptrace_entry),
when the task is traced by another thread.
The current code can only use ->ptrace_entry if it was untraced (by us).
Ugh. I finally realized just how magic the logic is there; thanks for
catching this. The call to forget_original_parent at the top of
exit_notify can potentially add the process to the list "dead" here,
either in exit_ptrace() or in reparent_leader() (the latter of which has
its own duplicate of part of exit_notify's logic, including
do_notify_parent and setting exit_state). Then exit_notify can add the
task to "dead" itself under some conditions that clearly depend on the
exact nature of the existing three-way conditional above. And finally
exit_notify loops over "dead" and releases all the tasks there.
I'll investigate this further and make sure the ptrace case gets
handled correctly.
- Josh Triplett