netdev - RE: sha512: make it work, undo percpu message schedule

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Date:	Fri, 13 Jan 2012 11:45:53 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Herbert Xu" <herbert@...dor.apana.org.au>
Cc:	"Alexey Dobriyan" <adobriyan@...il.com>,
	<linux-crypto@...r.kernel.org>, <netdev@...r.kernel.org>,
	<ken@...elabs.ch>,
	"Steffen Klassert" <steffen.klassert@...unet.com>
Subject: RE: sha512: make it work, undo percpu message schedule

 
> 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



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