linux-kernel - Re: [patch 0/2] Run interrupt handlers always with interrupts disabled

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: <20100326120620.GD19308@shareable.org>
Date:	Fri, 26 Mar 2010 12:06:20 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Nicolas Pitre <nico@...xnic.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...l.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Russell King <rmk@....linux.org.uk>
Subject: Re: [patch 0/2] Run interrupt handlers always with interrupts disabled

Nicolas Pitre wrote:
> On Fri, 26 Mar 2010, Peter Zijlstra wrote:
> 
> > On Fri, 2010-03-26 at 09:59 +0000, Alan Cox wrote:
> > > > As long as it's rare (which it is) i dont see a problem: you can enable 
> > > > interrupts in the handler by using local_irq_enable(), like the IDE PIO 
> > > > drivers do. That way it's documented a bit better as well, because it shows 
> > > > the precise source of the latency, with a big comment explaining it, etc.
> > > 
> > > I don't think it's as rare as you think particularly in embedded, and the
> > > moment you start explicitly using local_irq_enable() you've simply moved
> > > the underlying problem back and made it far harder to grep for.
> > 
> > We've got local_irq_enable_in_hardirq() which should be used and can
> > easily be grep'ed for.
> > 
> > But yes, I would much prefer to simply convert these known slow handlers
> > to threaded interrupts.
> 
> Can't do that.  The smc91x has a very small internal buffer which has to 
> be emptied using PIO.  Threaded interrupts simply have too high 
> latencies for overruns not to occur.  That's why the RX path is entirely 
> done in hardirq context while the TX path is done in softirq context.

Although I wouldn't be surprised to find threaded interrupts are too
slow on certain hardware, is that _fundamental_ to threaded
interrupts, or is it just that our implementation doesn't have the
funky hot path straight direct from hardirq -> running high priority
RT irq thread when it exceeds previously running priority?

In other words, can we swizzle threaded irqs into something more
resembling software-implemented hard irq priorities, while cunningly
updating the kernel state just enough to look like it's a thread?

-- Jamie
--
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/