On Fri, 2014-04-25 at 09:40 +0200, Mike Galbraith wrote:
> Hotplug can still deadlock in rt trees too, and will if you beat it
> hard.
Box actually deadlocks like so.
CPU3 boot.kdump
sys_wait4
do_wait
read_lock(&tasklist_lock)
rt_read_lock
__rt_spin_lock(lock)
migrate_disable()
pin_current_cpu()
if (hp->grab_lock) {
preempt_enable(); <== hmm
hotplug_lock(hp);
hp = &__get_cpu_var(hotplug_pcp); <== hmm
struct hotplug_pcp {
unplug = 0xffff8800b7d0e540,
sync_tsk = 0x0,
refcount = 0, <== hmm
grab_lock = 1,
...
lock = {
...
owner = 0xffff8802039f0001,
stress-cpu-hotplug_stress.sh?!?
<=== he's way over yonder.
Yo, dude, would you please NOT
take percpu locks with you?
CPU0 stress-cpu-hotplug_stress.sh
sysfs_write_file
dev_attr_store
online_store
device_offline
cpu_subsys_offline
cpu_down
_cpu_down
cpu_hotplug_begin
mutex_lock(&cpu_hotplug.lock);
...
check_for_tasks
write_lock_irq(&tasklist_lock);
held by CPU3 boot.kdump over there ===>
CPU0 kworker/0:0
cpuset_hotplug_workfn+0x23e/0x380
rebuild_sched_domains+0x15/0x30
rebuild_sched_domains_locked+0x17/0x80
get_online_cpus+0x35/0x50
mutex_lock(&cpu_hotplug.lock);
held by stress-cpu-hotplug_stress.sh
twiddle twiddle twiddle...
INFO: task kworker/0:0:4 blocked for more than 120 seconds.
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