Messages in this thread | | | Date | Mon, 30 May 2011 21:22:55 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 03/10] ptrace: implement PTRACE_SEIZE |
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On 05/27, Tejun Heo wrote: > > On Thu, May 26, 2011 at 05:01:50PM +0200, Oleg Nesterov wrote: > > On 05/26, Tejun Heo wrote: > > > > Or we can change do_wait() to detach a zombie leader. In this case it > > > > is not clear what should we do if the debugger is the real parent. > > > > Perhaps do_wait() should do the same: detach a leader (but not reap). > > > > When the last thread does, the real parent will be notified again. > > > > IOW, wait(tgid) can succeed twice. > > > > > > Just letting PTRACE_DETACH work for zombies sounds much simpler to me. > > > > Probably, but please note we have to modify do_wait() anyway. Otherwise > > in general the tracer simply can not know the tracee has exited. IOW, > > waitpid(zombie_leader_pid, WEXITED) should succeed without reaping if > > delay_group_leader(), then the tracer can do PTRACE_DETACH. But this is > > not symmetrical with sub-thread zombies. > > Yes, complicated. The task/process duality conflicts. wait(2) > already is different for group leader and succeeds twice for the > ptracer and the real parent (when they're different). > > If we relocate ptrace group leader zombie wait, as suggested, such > that it waits for the task itself rather than the whole group, we > would be taking away a feature - ptracer waiting for the whole process
Partly yes. The parent will be notified again and it can do another wait() later. The problem is, this is confusing.
> I think group leader wait becoming asymmetrical with sub-thread > zombies is perfectly fine - it already is.
Well, probably yes... But why? We have to change do_wait() anyway to report the death of the leader. If we do this, we can detach it as well.
> But would it be okay to > change ptrace wait(2) on group leader to wait for the task itself > rather than the whole group?
Yes, this is iffy. Simply because this can confuse the userspace. May be we can add W_PTRACED_THREAD_EXITED? (should be used instead of WEXITED by ptracer). Or, perhaps WEXITED should succeed but put something special into status?
Oleg.
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