Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH 4/5] freezer cgroup: Fix an RCU warning in cgroup_freezing_or_frozen() | From | Peter Zijlstra <> | Date | Fri, 23 Apr 2010 08:47:52 +0200 |
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On Fri, 2010-04-23 at 09:05 +0800, Li Zefan wrote: > > > You are right in that taking task_lock() is sufficient (I forgot > this lock rule), but it's not true that whatever locks are held > in the ->attach method can pin a task's cgroup.
Ah, can you be more specific about the ->attach() case?
The way I read it, cgroup_attach_task():
for_each_subsys(root, ss) { if (ss->attach) ss->attach(ss, cgrp, oldcgrp, tsk, false); } set_bit(CGRP_RELEASABLE, &oldcgrp->flags); synchronize_rcu(); put_css_set(cg);
So if you hold a lock that any of those ->attach() methods will use, it will in fact delay the put_css_set().
Ah, indeed I see your point, it doesn't indeed pin the task to the cgroup, but does avoid the cgroup from being freed.
Hrmm,.. so anything wanting to really pin a task to its cgroup will have to use task_lock()? I'll have to see if that works for sched_setscheduler().
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