linux-kernel - Re: [PATCH 02/10] random: use lockless techniques when mixing entropy pools

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Date:	Thu, 5 Jul 2012 11:19:56 -0700
From:	Greg KH <greg@...ah.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	torvalds@...ux-foundation.org, w@....eu, ewust@...ch.edu,
	zakir@...ch.edu, mpm@...enic.com, nadiah@...ucsd.edu,
	jhalderm@...ch.edu, tglx@...utronix.de, davem@...emloft.net
Subject: Re: [PATCH 02/10] random: use lockless techniques when mixing
 entropy pools

On Thu, Jul 05, 2012 at 02:12:05PM -0400, Theodore Ts'o wrote:
> The real-time Linux folks didn't like add_interrupt_randomness()
> taking a spinlock since it is called in the low-level interrupt
> routine.  Using atomic_t's and cmpxchg is also too expensive on some
> of the older architectures.  So we'll bite the bullet and use
> ACCESS_ONCE() and smp_rmb()/smp_wmb() to minimize the race windows
> when mixing in the entropy pool.
> 
> Also, we will use a trylock when trying to increase then entropy
> accounting during the interrupt path to avoid taking a spinlock there;
> if there is contention, we will simply not credit the entropy count,
> thus failing safe.  Thanks to Dan Carpenter for suggesting this
> approach.
> 
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> ---

Any reason you don't want this backported to the -stable series?

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