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

[Lai Jiangshan]

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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/