On Sun, 17 Feb 2013, Jiang Liu wrote:
> There's typical usage of si_meminfo as below:
> si_meminfo(&si);
> threshold = si->totalram - si.totalhigh;
>
> It may cause underflow if memory hotplug races with si_meminfo() because
> there's no mechanism to protect si_meminfo() from memory hotplug
> operations. And some callers expects that si_meminfo() is a lightweight
> operations. So introduce a lightweight mechanism to protect si_meminfo()
> from memory hotplug operations.
>
Instead of this, I think it would be appropriate to add a comment that
requires synchronization if two fields are going to be compared, i.e. use
{lock,unlock}_memory_hotplug() in the caller to si_meminfo(), or
appropriate underflow checking is done upon return.
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