From feb245e304f343cf5e4f9123db36354144dce8a4 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 16 Jun 2016 15:35:04 -0400 Subject: [PATCH] sched/core: Allow kthreads to fall back to online && !active cpus During CPU hotplug, CPU_ONLINE callbacks are run while the CPU is online but not active. A CPU_ONLINE callback may create or bind a kthread so that its cpus_allowed mask only allows the CPU which is being brought online. The kthread may start executing before the CPU is made active and can end up in select_fallback_rq(). In such cases, the expected behavior is selecting the CPU which is coming online; however, because select_fallback_rq() only chooses from active CPUs, it determines that the task doesn't have any viable CPU in its allowed mask and ends up overriding it to cpu_possible_mask. CPU_ONLINE callbacks should be able to put kthreads on the CPU which is coming online. Update select_fallback_rq() so that it follows cpu_online() rather than cpu_active() for kthreads. Reported-by: Gautham R Shenoy Tested-by: Gautham R. Shenoy Signed-off-by: Tejun Heo Signed-off-by: Peter Zijlstra (Intel) Cc: Abdul Haleem Cc: Aneesh Kumar Cc: Linus Torvalds Cc: Michael Ellerman Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kernel-team@fb.com Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20160616193504.GB3262@mtj.duckdns.org Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4135ac83cb65..51d7105f529a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1536,7 +1536,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p) for (;;) { /* Any allowed, online CPU? */ for_each_cpu(dest_cpu, tsk_cpus_allowed(p)) { - if (!cpu_active(dest_cpu)) + if (!(p->flags & PF_KTHREAD) && !cpu_active(dest_cpu)) + continue; + if (!cpu_online(dest_cpu)) continue; goto out; }