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Date: Fri, 23 Apr 2010 08:47:52 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Li Zefan <lizf@...fujitsu.com> Cc: paulmck@...ux.vnet.ibm.com, LKML <linux-kernel@...r.kernel.org>, "containers@...ts.osdl.org" <containers@...ts.osdl.org>, Paul Menage <menage@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Matt Helsley <matthltc@...ibm.com>, Cedric Le Goater <clg@...t.ibm.com> Subject: Re: [PATCH 4/5] freezer cgroup: Fix an RCU warning in cgroup_freezing_or_frozen() 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(). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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