linux-kernel - Re: [PATCH 1/3] comm: Introduce comm_lock seqlock to protect task->comm access

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Message-ID: <BANLkTin_MitzRUkWToj055AuAPdMC9msXQ@mail.gmail.com>
Date:	Sat, 14 May 2011 20:12:10 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, "Ted Ts'o" <tytso@....edu>,
	David Rientjes <rientjes@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Subject: Re: [PATCH 1/3] comm: Introduce comm_lock seqlock to protect
 task->comm access

>> 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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