linux-kernel - Re: [PATCH] Make rcutorture RNG use temporal entropy

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Message-ID: <20070823180658.GQ11166@waste.org>
Date:	Thu, 23 Aug 2007 13:06:58 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, bunk@...nel.org,
	josh@...nel.org, linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: [PATCH] Make rcutorture RNG use temporal entropy

On Fri, Aug 17, 2007 at 01:00:22PM -0700, Paul E. McKenney wrote:
> On Fri, Aug 17, 2007 at 11:53:56AM -0700, Andrew Morton wrote:
> > On Wed, 15 Aug 2007 19:49:04 -0700
> > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > 
> > > Repost of http://lkml.org/lkml/2007/8/10/472 made available by request.
> > > 
> > > The locking used by get_random_bytes() can conflict with the
> > > preempt_disable() and synchronize_sched() form of RCU.  This patch changes
> > > rcutorture's RNG to gather entropy from the new cpu_clock() interface
> > > (relying on interrupts, preemption, daemons, and rcutorture's reader
> > > thread's rock-bottom scheduling priority to provide useful entropy),
> > > and also adds and EXPORT_SYMBOL_GPL() to make that interface available
> > > to GPLed kernel modules such as rcutorture.
> > > 
> > > Passes several hours of rcutorture.
> > 
> > Please explain what "conflict with" means so that I can work out if
> > this is a needed-in-2.6.23 change, thanks.
> 
> Not needed in 2.6.23.  This change falls into the "preparation for -rt"
> category.  Also in the "don't unnecessarily eat entropy, leave some for
> the people needing crypographically secure randomness" category.

We've had several calls for a more fast and loose version of
get_random_bytes. Generalizing one of the cookie generation functions
is probably a good way to go.

-- 
Mathematics is the supreme nostalgia of our time.
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