Ccing The containers list because a related discussion is happening there and somehow this thread has never made it there. Ian Kent <raven@xxxxxxxxxx> writes: > On Mon, 2013-11-18 at 18:28 +0100, Oleg Nesterov wrote: >> On 11/15, Eric W. Biederman wrote: >> > >> > I don't understand that one. Having a preforked thread with the >> > proper >> > environment that can act like kthreadd in terms of spawning user >> > mode >> > helpers works and is simple. > > Forgive me replying to such an old thread but ... > > After realizing workqueues can't be used to pre-create threads to run > usermode helpers I've returned to look at this. If someone can wind up with a good implementation I will be happy. >> Can't we ask ->child_reaper to create the non-daemonized kernel thread >> with the "right" ->nsproxy, ->fs, etc? > > Eric, do you think this approach would be sufficient too? > > Probably wouldn't be quite right for user namespaces but should provide > what's needed for other cases? > > It certainly has the advantage of not having to maintain a plague of > processes waiting around to execute helpers. That certainly sounds attractive. Especially for the case of everyone who wants to set a core pattern in a container. I am fuzzy on all of the details right now, but what I do remember is that in the kernel the user mode helper concepts when they attempted to scrub a processes environment were quite error prone until we managed to get kthreadd(pid 2) on the scene which always had a clean environment. If we are going to tie this kind of thing to the pid namespace I recommend simplying denying it if you are in a user namespace without an approrpriate pid namespace. AKA simply not allowing thigns to be setup if current->pid_ns->user_ns != current->user_ns. That still leaves things a little hand-wavy but I hope that helps conceptually. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
