* Re: CGROUP 관련 문의 [not found] <1286806.131871377667197297.JavaMail.weblogic@epv6ml01> @ 2013-08-28 13:40 ` Tejun Heo 2013-09-08 16:00 ` Oleg Nesterov 0 siblings, 1 reply; 2+ messages in thread From: Tejun Heo @ 2013-08-28 13:40 UTC (permalink / raw) To: 김은기, Oleg Nesterov Cc: linux-kernel, Li Zefan, containers, cgroups Hey, oleg. Eunki is reporting a stall in the following loop in kernel/cgroup.c::cgroup_attach_task() On Wed, Aug 28, 2013 at 05:19:57AM +0000, 김은기 wrote: > > --------------------------------------------------------------------------- > rcu_read_lock(); > do { > struct task_and_cgroup ent; > > /* @tsk either already exited or can't exit until the end */ > if (tsk->flags & PF_EXITING) > continue; > > /* as per above, nr_threads may decrease, but not increase. */ > BUG_ON(i >= group_size); > ent.task = tsk; > ent.cgrp = task_cgroup_from_root(tsk, root); > /* nothing to do if this task is already in the cgroup */ > if (ent.cgrp == cgrp) > continue; > /* > * saying GFP_ATOMIC has no effect here because we did prealloc > * earlier, but it's good form to communicate our expectations. > */ > retval = flex_array_put(group, i, &ent, GFP_ATOMIC); > BUG_ON(retval != 0); > i++; > > if (!threadgroup) > break; > } while_each_thread(leader, tsk); > --------------------------------------------------------------------------------------------- where the iteration goes like leader -> Task1 -> Task2 -> Task3 -> Task1 ie. leader seems RCU unlinked. Looking at the users of while_each_thread(), I'm confused about its locking requirements. Does it require tasklist_lock or is rcu read lock enough? If there are special requirements, it'd be great if it can be described in the comment above the two macros. Eunki, can you please post full stack dump from such lockups? Where is the function called from? Is it from attach_task_by_pid() or other places? Apparently, we aren't holding threadgroup_lock from other callsites so the leader isn't guaranteed to be / stay the leader. Thanks. -- tejun ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: CGROUP 관련 문의 2013-08-28 13:40 ` CGROUP 관련 문의 Tejun Heo @ 2013-09-08 16:00 ` Oleg Nesterov 0 siblings, 0 replies; 2+ messages in thread From: Oleg Nesterov @ 2013-09-08 16:00 UTC (permalink / raw) To: Tejun Heo Cc: 김은기, linux-kernel, Li Zefan, containers, cgroups Hi Tejun, Sorry for delay, vacation. On 08/28, Tejun Heo wrote: > > Hey, oleg. > > Eunki is reporting a stall in the following loop in > kernel/cgroup.c::cgroup_attach_task() > > On Wed, Aug 28, 2013 at 05:19:57AM +0000, 김은기 wrote: > > > > --------------------------------------------------------------------------- > > rcu_read_lock(); > > do { > > struct task_and_cgroup ent; > > > > /* @tsk either already exited or can't exit until the end */ > > if (tsk->flags & PF_EXITING) > > continue; > > > > /* as per above, nr_threads may decrease, but not increase. */ > > BUG_ON(i >= group_size); > > ent.task = tsk; > > ent.cgrp = task_cgroup_from_root(tsk, root); > > /* nothing to do if this task is already in the cgroup */ > > if (ent.cgrp == cgrp) > > continue; > > /* > > * saying GFP_ATOMIC has no effect here because we did prealloc > > * earlier, but it's good form to communicate our expectations. > > */ > > retval = flex_array_put(group, i, &ent, GFP_ATOMIC); > > BUG_ON(retval != 0); > > i++; > > > > if (!threadgroup) > > break; > > } while_each_thread(leader, tsk); > > --------------------------------------------------------------------------------------------- > > where the iteration goes like > > leader -> Task1 -> Task2 -> Task3 -> Task1 > > ie. leader seems RCU unlinked. Looking at the users of > while_each_thread(), I'm confused about its locking requirements. In short: it is broken. This was already discussed several times but every time I was distracted. I already have the patches somewhere (probably not 100% finished), will try to return to this problem soon. Oleg. ^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2013-09-08 16:06 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
[not found] <1286806.131871377667197297.JavaMail.weblogic@epv6ml01>
2013-08-28 13:40 ` CGROUP 관련 문의 Tejun Heo
2013-09-08 16:00 ` Oleg Nesterov
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox