linux-kernel - Re: Proposal: HAVE_SEPARATE_IRQ

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Message-ID: <alpine.DEB.2.20.1611092227200.3501@nanos>
Date:   Wed, 9 Nov 2016 22:40:24 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
cc:     LKML <linux-kernel@...r.kernel.org>, linux-mips@...ux-mips.org,
        linux-mm@...ck.org,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>,
        k@...ka.home.kg
Subject: Re: Proposal: HAVE_SEPARATE_IRQ_STACK?

On Wed, 9 Nov 2016, Jason A. Donenfeld wrote:
> But for the remaining platforms, such as MIPS, this is still a
> problem. In an effort to work around this in my code, rather than
> having to invoke kmalloc for what should be stack-based variables, I
> was thinking I'd just disable preemption for those functions that use
> a lot of stack, so that stack-hungry softirq handlers don't crush it.
> This is generally unsatisfactory, so I don't want to do this
> unconditionally. Instead, I'd like to do some cludge such as:
> 
>     #ifndef CONFIG_HAVE_SEPARATE_IRQ_STACK
>     preempt_disable();

That preempt_disable() prevents merily preemption as the name says, but it
wont prevent softirq handlers from running on return from interrupt. So
what's the point?

> However, for this to work, I actual need that config variable. Would
> you accept a patch that adds this config variable to the relavent
> platforms?

It might have been a good idea, to cc all relevant arch maintainers on
that ...

> If not, do you have a better solution for me (which doesn't
> involve using kmalloc or choosing a different crypto primitive)?

What's wrong with using kmalloc?

Thanks,

	tglx