Re: [PATCH 1/3] comm: Introduce comm_lock seqlock to protecttask->comm access

[KOSAKI Motohiro]

>> Can you please explain why we should use seqlock? That said,
>> we didn't use seqlock for /proc items. because, plenty seqlock
>> write may makes readers busy wait. Then, if we don't have another
>> protection, we give the local DoS attack way to attackers.
>
> So you're saying that heavy write contention can cause reader
> starvation?

Yes.

>> task->comm is used for very fundamentally. then, I doubt we can
>> assume write is enough rare. Why can't we use normal spinlock?
>
> I think writes are likely to be fairly rare. Tasks can only name
> themselves or sibling threads, so I'm not sure I see the risk here.

reader starvation may cause another task's starvation if reader have
an another lock.
And, "only sibling" don't make any security gurantee as I said past.

Thanks.
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