Re: [PATCH] cpusets: fix deadlock with cpu_down()->cpuset_lock()

Lai Jiangshan
2009-07-30T01:53:22Z

Oleg Nesterov wrote:
> On 07/29, Oleg Nesterov wrote:
>> I strongly believe the bug does exist, but this patch needs the review
>> from maintainers.
>
> Yes...
>
>> IOW, with this patch migration_call(CPU_DEAD) runs without callback_mutex,
>> but kernel/cpuset.c always takes get_online_cpus() before callback_mutex.
>
> Oh. I'm afraid this is not an option.
>
> callback_mutex should nest under cgroup_mutex, but cpu hotplu pathes
> take cgroup_mutex under cpu_hotplug->lock. Lockdep won't be happy.
>
> Oleg.
>

We have made great effort to remove get_online_cpus() from cgroup_mutex
critical region.

We can migrate the owner of callback_mutex in migration_call(CPU_DEAD)
at first(and then take callback_mutex and migrate others).
It fixes this bug, but it can't help for your
"cpu_hotplug: don't play with current->cpus_allowed" patch.

Lai.