netdev - Re: [PATCH] net: net_secret should not depend on TCP

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Message-ID: <20130924152858.GB1527@order.stressinduktion.org>
Date:	Tue, 24 Sep 2013 17:28:58 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>, davem@...emloft.net,
	netdev@...r.kernel.org, jesse.brandeburg@...el.com
Subject: Re: [PATCH] net: net_secret should not depend on TCP

On Tue, Sep 24, 2013 at 08:22:27AM -0700, Eric Dumazet wrote:
> On Tue, 2013-09-24 at 17:13 +0200, Hannes Frederic Sowa wrote:
> > On Tue, Sep 24, 2013 at 06:19:57AM -0700, Eric Dumazet wrote:
> > > -void net_secret_init(void)
> > > +static u32 net_secret[NET_SECRET_SIZE] ____cacheline_aligned;
> > > +
> > > +static void net_secret_init(void)
> > >  {
> > > -	get_random_bytes(net_secret, sizeof(net_secret));
> > > +	u32 tmp;
> > > +	int i;
> > > +
> > > +	if (likely(net_secret[0]))
> > > +		return;
> > > +
> > > +	for (i = NET_SECRET_SIZE; i > 0;) {
> > > +		do {
> > > +			get_random_bytes(&tmp, sizeof(tmp));
> > > +		} while (!tmp);
> > 
> > I am afraid we can block here on embedded systems in an atomic section? Is
> > this actually an issue? It does get called in a spin_lock_h.
> 
> I do not see issues : get_random_bytes() is irq safe.

But couldn't it be that get_random_bytes always returns 0 and we won't make
any progress here. Does the reseed happen from irq context or from softirqs? I
always thought it would be from a softirq (which could be blocked).

Thanks,

  Hannes
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