Messages in this thread | | | Date | Sat, 15 Mar 2014 08:49:37 -0400 | From | Peter Hurley <> | Subject | Re: pppd service crash in linux-3.13.6 |
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On 03/14/2014 05:04 PM, Oleg Nesterov wrote: > On 03/14, Peter Hurley wrote: >> On 03/14/2014 03:23 PM, Oleg Nesterov wrote: >>> On 03/14, Peter Hurley wrote: >>>> >> Yes, cgroup_release_agent() is the work function that is scheduled. >> >>>> which requires both namespace and tty facilities. >>> >>> Hmm... why? >>> >>> The exiting task obviously can't exec. The only way to spawn a userspace >>> process is call_usermodehelper(), it should work just fine, no? >> >> You're correct, in the immediate sense that the user command exec'd will >> not inherit open file descriptors. >> >> But what if it expects to be able to find the intact children of >> the foreground process group, and can't because the controlling tty >> has already been torn down and all the children already sent SIGHUP. > > Which group/tty ? call_usermodehelper() asks the workqueue thread > to kthread_create/exec. See also below... > >> Or what if the user command expects to find and join the user namespace >> of the dying process but now it's already been freed? > > But it can't even know who called call_usermodehelper(). Besides, > cgroup_release_agent() uses UMH_WAIT_EXEC, so the caller can continue > and disappear completely before the usermode process has any chance > to do something.
I'm just hypothesizing potential breakage, since the order of teardown is sensitive to changes, and I didn't do a complete audit of all the possibilities.
If you feel strongly about moving disassociate_tty(), I won't object.
Regards, Peter Hurley
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