Messages in this thread Patch in this message |  | | | Date | Fri, 06 Nov 2009 11:43:41 +0800 | | From | Lai Jiangshan <> | | Subject | [PATCH -tip] sched: fix bug that task run on a wrong and unallowed cpu |
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a1f84a3ab8e002159498814eaa7e48c33752b04b brought a bug that task may run on a unallowed cpu.
In my box, this bug trigger debug_smp_processor_id()'s complaints:
BUG: using smp_processor_id() in preemptible [00000000] code: events/1/10 caller is vmstat_update+0x2a/0x3e Pid: 10, comm: events/1 Not tainted 2.6.32-rc6-tip-01796-gd995f1d-dirty #118 Call Trace: [<c02a3871>] debug_smp_processor_id+0xa5/0xbc [<c01a229e>] vmstat_update+0x2a/0x3e [<c014d6df>] worker_thread+0x134/0x1c2 [<c01a2274>] ? vmstat_update+0x0/0x3e [<c0151361>] ? autoremove_wake_function+0x0/0x38 [<c014d5ab>] ? worker_thread+0x0/0x1c2 [<c0151298>] kthread+0x66/0x6e [<c0151232>] ? kthread+0x0/0x6e [<c0102e97>] kernel_thread_helper+0x7/0x10 See: debug_smp_processor_id() { ..... /* * Kernel threads bound to a single CPU can safely use * smp_processor_id(): */ if (cpumask_equal(¤t->cpus_allowed, cpumask_of(this_cpu))) goto out; ..... } When events/1 run on wrong cpu, cpumask_equal() will fail, and debug_smp_processor_id() complains.
Ftrace also shows events/1 was run on wrong cpu(cpu#0):
<idle>-0 [000] 947.573038: perf_event_task_sched_out <-schedule <idle>-0 [000] 947.573039: memcpy <-tracing_record_cmdline <idle>-0 [000] 947.573040: __switch_to <-schedule events/1-10 [000] 947.573050: finish_task_switch <-schedule events/1-10 [000] 947.573051: perf_event_task_sched_in <-finish_task_switch events/1-10 [000] 947.573051: _spin_unlock_irq <-finish_task_switch events/1-10 [000] 947.573052: finish_wait <-worker_thread events/1-10 [000] 947.573053: kthread_should_stop <-worker_thread events/1-10 [000] 947.573054: _spin_lock_irq <-worker_thread events/1-10 [000] 947.573055: _spin_lock_irqsave <-probe_workqueue_execution events/1-10 [000] 947.573056: _spin_unlock_irqrestore <-probe_workqueue_execution events/1-10 [000] 947.573057: _spin_unlock_irq <-worker_thread events/1-10 [000] 947.573058: flush_to_ldisc <-worker_thread
events/1 should run at cpu#1, but [000] shows it was run at cpu#0
After a1f84a3ab8e002159498814eaa7e48c33752b04b applied, select_task_rq_fair() select candidate cpu without checking the p->cpus_allowed. This fix repair it.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> --- diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 32f06ed..6a8f389 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1414,7 +1414,8 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag } if (candidate == -1 || candidate == cpu) { - for_each_cpu(i, sched_domain_span(tmp)) { + for_each_cpu_and(i, sched_domain_span(tmp), + &p->cpus_allowed) { if (!cpu_rq(i)->cfs.nr_running) { candidate = i; break;
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