linux-kernel - cpuset: attach_task() vs sched

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Date:	Sat, 25 Aug 2007 20:26:06 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Cliff Wickman <cpw@....com>, Paul Jackson <pj@....com>,
	Paul Menage <menage@...gle.com>
Cc:	linux-kernel@...r.kernel.org
Subject: cpuset: attach_task() vs sched_setaffinity() race?

After the brief look at kernel/cpuset.c, it seems that attach_task() should
guarantee that the task can't use CPUs outside of cpuset->cpus_allowed.

But this looks racy wrt sched_setaffinity() which does

	cpus_allowed = cpuset_cpus_allowed(p);
	// callback_mutex is free
	set_cpus_allowed(p);

What if attach_task()->set_cpus_allowed() happens in between?

Another question: update_cpumask(cs) does nothing with the tasks attached to
that cpuset, why? It may take a while before the task actually migrates to the
new CPU.

Thanks,

Oleg.

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