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 explicitly. 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/ |