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
--
---------------------------------
Sachin Sant
IBM Linux Technology Center
India Systems and Technology Labs
Bangalore, India
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