Prev: sched: implement __set_cpus_allowed()
Next: [PATCH] ioctl for getting RS485 information on Cris architecture
From: Peter Zijlstra on 31 May 2010 04:10
On Thu, 2010-05-13 at 12:48 +0200, Tejun Heo wrote:
> If called after sched_class chooses a CPU which isn't in a task's
> cpus_allowed mask, select_fallback_rq() can end up migrating a task
> which is bound to an !active but online cpu to an active cpu. This is
> dangerous because active is cleared before CPU_DOWN_PREPARE is called
> and subsystems expect affinities of kthreads and other tasks to be
> maintained till their CPU_DOWN_PREPARE callbacks are complete.
So 6ad4c188 (sched: Fix balance vs hotplug race) moved it that early
because it was done too late.
Could we not instead do it explicitly after CPU_DOWN_PREPARE? It would
of course mean removing the partition_sched_domain() and
generate_sched_domains() calls from these callbacks and doing it
So we need to do it before we take the CPU down, but I think we can do
it after DOWN_PREPARE.
> Consult cpu_online_mask instead.
> This problem is triggered by cmwq. During CPU_DOWN_PREPARE, hotplug
> callback creates the trustee kthread and kthread_bind()s it to the
> target cpu, and the trustee is expected to run on that cpu.
It doesn't explain wth a trustee kthread is, which pretty much renders
the whole paragraph useless.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/