From: "David Laight" <David.Laight@ACULAB.COM>
Subject: RE: sha512: make it work, undo percpu message schedule
Date: Fri, 13 Jan 2012 11:45:53 -0000
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Cc: "Alexey Dobriyan" <adobriyan@gmail.com>,
	<linux-crypto@vger.kernel.org>, <netdev@vger.kernel.org>,
	<ken@codelabs.ch>,
	"Steffen Klassert" <steffen.klassert@secunet.com>
To: "Eric Dumazet" <eric.dumazet@gmail.com>,
	"Herbert Xu" <herbert@gondor.apana.org.au>
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> Trying a dynamic memory allocation, and fallback on a single
> pre-allocated bloc of memory, shared by all cpus, protected by a
> spinlock
...
> -
> +	static u64 msg_schedule[80];
> +	static DEFINE_SPINLOCK(msg_schedule_lock);
>  	int i;
> -	u64 *W = get_cpu_var(msg_schedule);
> +	u64 *W = kzalloc(sizeof(msg_schedule), GFP_ATOMIC |
__GFP_NOWARN);
>  
> +	
> +	if (!W) {
> +		spin_lock_bh(&msg_schedule_lock);
> +		W = msg_schedule;
> +	}

If this code can be called from an ISR is the kmalloc()
call safe?

If the above is safe, wouldn't it be better to:
1) try to use the static buffer
2) try to kalloc() a buffer
3) spinwait for the static buffer to be free

	David