Messages in this thread Patch in this message | | | From | KOSAKI Motohiro <> | Subject | [PATCH 1/2] cpuset: fix cpuset_cpus_allowed_fallback() don't update tsk->rt.nr_cpus_allowed | Date | Mon, 2 May 2011 19:55:23 +0900 (JST) |
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The rule is, we have to update tsk->rt.nr_cpus_allowed too if we change tsk->cpus_allowed. Otherwise RT scheduler may confuse.
This patch fixes it.
btw, system_state checking is very important. current boot sequence is (1) smp_init (ie secondary cpus up and created cpu bound kthreads). (2) sched_init_smp(). Then following bad scenario can be happen,
(1) cpuup call notifier(CPU_UP_PREPARE) (2) A cpu notifier consumer create FIFO kthread (3) It call kthread_bind() ... but, now secondary cpu haven't ONLINE (3) schedule() makes fallback and cpuset_cpus_allowed_fallback change task->cpus_allowed (4) find_lowest_rq() touch local_cpu_mask if task->rt.nr_cpus_allowed != 1, but it haven't been initialized.
RCU folks plan to introduce such FIFO kthread and our testing hitted the above issue. Then this patch also protect it.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Ingo Molnar <mingo@elte.hu> --- include/linux/cpuset.h | 1 + kernel/cpuset.c | 1 + kernel/sched.c | 4 ++++ 3 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index f20eb8f..42dcbdc 100644 --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -147,6 +147,7 @@ static inline void cpuset_cpus_allowed(struct task_struct *p, static inline int cpuset_cpus_allowed_fallback(struct task_struct *p) { cpumask_copy(&p->cpus_allowed, cpu_possible_mask); + p->rt.nr_cpus_allowed = cpumask_weight(&p->cpus_allowed); return cpumask_any(cpu_active_mask); } diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 1ceeb04..6e5bbe8 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -2220,6 +2220,7 @@ int cpuset_cpus_allowed_fallback(struct task_struct *tsk) cpumask_copy(&tsk->cpus_allowed, cpu_possible_mask); cpu = cpumask_any(cpu_active_mask); } + tsk->rt.nr_cpus_allowed = cpumask_weight(&tsk->cpus_allowed); return cpu; } diff --git a/kernel/sched.c b/kernel/sched.c index fd4625f..bfcd219 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2352,6 +2352,10 @@ static int select_fallback_rq(int cpu, struct task_struct *p) if (dest_cpu < nr_cpu_ids) return dest_cpu; + /* Don't worry. It's temporary mismatch. */ + if (system_state < SYSTEM_RUNNING) + return cpu; + /* No more Mr. Nice Guy. */ dest_cpu = cpuset_cpus_allowed_fallback(p); /* -- 1.7.3.1
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