Messages in this thread Patch in this message |  | | | From | Tejun Heo <> | | Subject | [PATCH 1/4] sched: consult online mask instead of active in select_fallback_rq() | | Date | Thu, 13 May 2010 12:48:22 +0200 |
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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.
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.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@elte.hu> --- kernel/sched.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index b531d79..aca4a20 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2262,12 +2262,12 @@ static int select_fallback_rq(int cpu, struct task_struct *p) const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(cpu)); /* Look for allowed, online CPU in same node. */ - for_each_cpu_and(dest_cpu, nodemask, cpu_active_mask) + for_each_cpu_and(dest_cpu, nodemask, cpu_online_mask) if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed)) return dest_cpu; /* Any allowed, online CPU? */ - dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask); + dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_online_mask); if (dest_cpu < nr_cpu_ids) return dest_cpu; -- 1.6.4.2
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