Re: node-hotplug: is memset 0 safe in try_offline_node()?
From: Gu Zheng
Date: Tue Mar 03 2015 - 05:37:43 EST
Hi Xishi,
On 03/03/2015 11:30 AM, Xishi Qiu wrote:
> When hot-remove a numa node, we will clear pgdat,
> but is memset 0 safe in try_offline_node()?
It is not safe here. In fact, this is a temporary solution here.
As you know, pgdat is accessed lock-less now, so protection
mechanism (RCUï) is needed to make it completely safe here,
but it seems a bit over-kill.
>
> process A: offline node XX:
> for_each_populated_zone()
> find online node XX
> cond_resched()
> offline cpu and memory, then try_offline_node()
> node_set_offline(nid), and memset(pgdat, 0, sizeof(*pgdat))
> access node XX's pgdat
> NULL pointer access error
It's possible, but I did not meet this condition, did you?
Regards,
Gu
>
> Thanks,
> Xishi Qiu
>
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