linux-kernel - Re: lockdep and threaded IRQs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1236035221.5330.1798.camel@laptop>
Date:	Tue, 03 Mar 2009 00:07:01 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>,
	dbrownell@...rs.sourceforge.net, tglx@...utronix.de,
	me@...ipebalbi.com, linux-kernel@...r.kernel.org,
	linux-input@...r.kernel.org, felipe.balbi@...ia.com,
	dmitry.torokhov@...il.com, sameo@...nedhand.com
Subject: Re: lockdep and threaded IRQs

On Mon, 2009-03-02 at 14:57 -0800, Andrew Morton wrote:
> On Mon, 02 Mar 2009 14:46:47 -0800 (PST)
> David Miller <davem@...emloft.net> wrote:
> 
> > From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Date: Mon, 02 Mar 2009 23:19:31 +0100
> > 
> > > I state that every !IRQF_DISABLED usage is a bug, either due to broken
> > > hardware or broken drivers.
> > 
> > We'll send you the bill to have everyone's hardware
> > replaced :-)
> 
> yes, but with what?
> 
> No matter how fast all our interrupt handlers are, running them with
> local interrupts disabled has to worsen the worst-case interrupt
> latency.
> 
> I don't see how removing !IRQF_DISABLED improves the kernel - in fact
> there's a latency argument for making !IRQF_DISABLED the default.

On preempt-rt all we do in the hardirq path is mask the interrupt line
and wake up a thread. That's the extreme end of low latency interrupts.

Arguably there is a middle way that works for !-rt.

However, striving to enable interrupts in all interrupt handlers is
asking for stack overruns. Interrupt nesting just isn't really helpful.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/