linux-kernel - Re: [patch 05/11] syslets: core code

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Date:	14 Feb 2007 00:15:58 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 05/11] syslets: core code

Ingo Molnar <mingo@...e.hu> writes:

> +
> +static struct async_thread *
> +pick_ready_cachemiss_thread(struct async_head *ah)

The cachemiss names are confusing. I assume that's just a left over
from Tux?
> +
> +	memset(atom->args, 0, sizeof(atom->args));
> +
> +	ret |= __get_user(arg_ptr, &uatom->arg_ptr[0]);
> +	if (!arg_ptr)
> +		return ret;
> +	if (!access_ok(VERIFY_WRITE, arg_ptr, sizeof(*arg_ptr)))
> +		return -EFAULT;

It's a little unclear why you do that many individual access_ok()s.
And why is the target constant sized anyways?


+	/*
+	 * Lock down the ring. Note: user-space should not munlock() this,
+	 * because if the ring pages get swapped out then the async
+	 * completion code might return a -EFAULT instead of the expected
+	 * completion. (the kernel safely handles that case too, so this
+	 * isnt a security problem.)
+	 *
+	 * mlock() is better here because it gets resource-accounted
+	 * properly, and even unprivileged userspace has a few pages
+	 * of mlock-able memory available. (which is more than enough
+	 * for the completion-pointers ringbuffer)
+	 */

If it's only a few pages you don't need any resource accounting.
If it's more then it's nasty to steal the users quota.
I think plain gup() would be better.


-Andi
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