Messages in this thread Patch in this message | | | From | "Eric W. Biederman" <> | Date | Mon, 06 Jun 2022 17:10:02 -0500 | Subject | Re: [PATCH 07/16] signal: Wake up the designated parent |
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Oleg Nesterov <oleg@redhat.com> writes:
> On 05/24, Oleg Nesterov wrote: >> >> On 05/24, Oleg Nesterov wrote: >> > >> > I fail to understand this patch... >> > >> > On 05/18, Eric W. Biederman wrote: >> > > >> > > Today if a process is ptraced only the ptracer will ever be woken up in >> > > wait >> > >> > and why is this wrong? >> > >> > > Fixes: 75b95953a569 ("job control: Add @for_ptrace to do_notify_parent_cldstop()") >> > >> > how does this change fix 75b95953a569? >> >> OK, I guess you mean the 2nd do_notify_parent_cldstop() in ptrace_stop(), >> the problematic case is current->ptrace == T. Right? >> >> I dislike this patch anyway, but let me think more about it. > > OK, now that I understand the problem, the patch doesn't look bad to me, > although I'd ask to make the changelog more clear.
I will see what I can do.
> After this change __wake_up_parent() can't accept any "parent" from > p->parent thread group, but all callers look fine except > ptrace_detach().
Having looked at it a little more I think the change was too restrictive. For the !ptrace_reparented case there are possibly two threads of the parent process that wait_consider_task will allow to wait even with __WNOTHREAD specified. It is desirable to wake them both up.
Which if I have had enough sleep reduces this patch to just:
diff --git a/kernel/exit.c b/kernel/exit.c index f072959fcab7..c8156366b722 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1431,8 +1431,10 @@ static int child_wait_callback(wait_queue_entry_t *wait, unsigned mode, if (!eligible_pid(wo, p)) return 0; - if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent) - return 0; + if ((wo->wo_flags & __WNOTHREAD) && + (wait->private != p->parent) && + (wait->private != p->real_parent)) + return 0; return default_wake_function(wait, mode, sync, key); }
I think that solves the issue without missing wake-ups without adding any more.
For the same set of reasons it looks like the __wake_up_parent in __ptrace_detach is just simply dead code. I don't think there is a case where when !ptrace_reparented the thread that is the real_parent can sleep in do_wait when the thread that was calling ptrace could not.
That needs a very close look to confirm.
Eric
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