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Message-ID: <alpine.DEB.0.9999.0710062250590.11526@chino.kir.corp.google.com> Date: Sat, 6 Oct 2007 23:15:14 -0700 (PDT) From: David Rientjes <rientjes@...gle.com> To: Paul Menage <menage@...gle.com> cc: Paul Jackson <pj@....com>, Andrew Morton <akpm@...ux-foundation.org>, nickpiggin@...oo.com.au, a.p.zijlstra@...llo.nl, serue@...ibm.com, clg@...ibm.com, linux-kernel@...r.kernel.org, ebiederm@...ssion.com, svaidy@...ux.vnet.ibm.com, xemul@...nvz.org, containers@...ts.osdl.org, balbir@...ux.vnet.ibm.com Subject: Re: [PATCH] task containersv11 add tasks file interface fix for cpusets On Sat, 6 Oct 2007, Paul Menage wrote: > > The getting and putting of the tasks will prevent them from exiting or > > being deallocated prematurely. But this is also a critical section that > > will need to be protected by some mutex so it doesn't race with other > > set_cpus_allowed(). > > Is that necessary? If some other process calls set_cpus_allowed() > concurrently with a cpuset cpus update, it's not clear that there's > any defined serialization semantics that have to be achieved, as long > as the end result is that the task's cpus_allowed are within the > cpuset's cpus_allowed. > It can race with sched_setaffinity(). It has to give up tasklist_lock as well to call set_cpus_allowed() and can race cpus_allowed = cpuset_cpus_allowed(p); cpus_and(new_mask, new_mask, cpus_allowed); retval = set_cpus_allowed(p, new_mask); and allow a task to have a cpu outside of the cpuset's new cpus_allowed if you've taken it away between cpuset_cpus_allowed() and set_cpus_allowed(). David - 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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