Messages in this thread | | | Date | Tue, 15 Dec 2009 15:14:11 +0530 | From | Sachin Sant <> | Subject | Re: [Next] CPU Hotplug test failures on powerpc |
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Benjamin Herrenschmidt wrote: >> static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p) >> { >> int dest_cpu; >> const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(dead_cpu)); >> >> again: >> /* Look for allowed, online CPU in same node. */ >> for_each_cpu_and(dest_cpu, nodemask, cpu_active_mask) >> if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed)) >> goto move; >> >> /* Any allowed, online CPU? */ >> dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask); >> if (dest_cpu < nr_cpu_ids) >> goto move; >> >> /* No more Mr. Nice Guy. */ >> if (dest_cpu >= nr_cpu_ids) { >> cpuset_cpus_allowed_locked(p, &p->cpus_allowed); >> ====> dest_cpu = cpumask_any_and(cpu_active_mask, &p->cpus_allowed); >> >> /* >> * Don't tell them about moving exiting tasks or >> * kernel threads (both mm NULL), since they never >> * leave kernel. >> */ >> if (p->mm && printk_ratelimit()) { >> pr_info("process %d (%s) no longer affine to cpu%d\n", >> task_pid_nr(p), p->comm, dead_cpu); >> } >> } >> >> move: >> /* It can have affinity changed while we were choosing. */ >> if (unlikely(!__migrate_task_irq(p, dead_cpu, dest_cpu))) >> goto again; >> } >> >> Both masks, p->cpus_allowed and cpu_active_mask are stable in that p >> won't go away since we hold the tasklist_lock (in migrate_list_tasks), >> and cpu_active_mask is static storage, so WTH is it going funny on? >> I added some debug statements within the above code. This is a 2 cpu machine.
XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2 XMON dest_cpu = 1024 XMON dest_cpu = 1024 . dead_cpu = 1 XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2 XMON dest_cpu = 1024 XMON dest_cpu = 1024 . dead_cpu = 1 XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2 XMON dest_cpu = 1024 XMON dest_cpu = 1024 . dead_cpu = 1
Seems to me that the control is stuck in an infinite loop and hence the machine appears to be in hung state. The dest_cpu value is always 1024 and never changes, which result in an infinite loop.
In working scenario the o/p is something on the following lines
XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2 XMON dest_cpu = 0 XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2 XMON dest_cpu = 0 XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2 XMON dest_cpu = 0
Let me know if i should try to record any specific value ?
Thanks -Sachin
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--------------------------------- Sachin Sant IBM Linux Technology Center India Systems and Technology Labs Bangalore, India ---------------------------------
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