4.14-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 175f0e25abeaa2218d431141ce19cf1de70fa82d ]
As already enforced by the WARN() in __set_cpus_allowed_ptr(), the rules for running on an online && !active CPU are stricter than just being a kthread, you need to be a per-cpu kthread.
If you're not strictly per-CPU, you have better CPUs to run on and don't need the partially booted one to get your work done.
The exception is to allow smpboot threads to bootstrap the CPU itself and get kernel 'services' initialized before we allow userspace on it.
Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Paul E. McKenney paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Steven Rostedt rostedt@goodmis.org Cc: Tejun Heo tj@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Fixes: 955dbdf4ce87 ("sched: Allow migrating kthreads into online but inactive CPUs") Link: http://lkml.kernel.org/r/20170725165821.cejhb7v2s3kecems@hirez.programming.k... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/core.c | 42 ++++++++++++++++++++++++++++++------------ 1 file changed, 30 insertions(+), 12 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -894,6 +894,33 @@ void check_preempt_curr(struct rq *rq, s }
#ifdef CONFIG_SMP + +static inline bool is_per_cpu_kthread(struct task_struct *p) +{ + if (!(p->flags & PF_KTHREAD)) + return false; + + if (p->nr_cpus_allowed != 1) + return false; + + return true; +} + +/* + * Per-CPU kthreads are allowed to run on !actie && online CPUs, see + * __set_cpus_allowed_ptr() and select_fallback_rq(). + */ +static inline bool is_cpu_allowed(struct task_struct *p, int cpu) +{ + if (!cpumask_test_cpu(cpu, &p->cpus_allowed)) + return false; + + if (is_per_cpu_kthread(p)) + return cpu_online(cpu); + + return cpu_active(cpu); +} + /* * This is how migration works: * @@ -951,16 +978,8 @@ struct migration_arg { static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf, struct task_struct *p, int dest_cpu) { - if (p->flags & PF_KTHREAD) { - if (unlikely(!cpu_online(dest_cpu))) - return rq; - } else { - if (unlikely(!cpu_active(dest_cpu))) - return rq; - } - /* Affinity changed (again). */ - if (!cpumask_test_cpu(dest_cpu, &p->cpus_allowed)) + if (!is_cpu_allowed(p, dest_cpu)) return rq;
update_rq_clock(rq); @@ -1489,10 +1508,9 @@ static int select_fallback_rq(int cpu, s for (;;) { /* Any allowed, online CPU? */ for_each_cpu(dest_cpu, &p->cpus_allowed) { - if (!(p->flags & PF_KTHREAD) && !cpu_active(dest_cpu)) - continue; - if (!cpu_online(dest_cpu)) + if (!is_cpu_allowed(p, dest_cpu)) continue; + goto out; }