linux-kernel - Re: serial flow control appears broken

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: <20070730095933.GA20417@flint.arm.linux.org.uk>
Date:	Mon, 30 Jul 2007 10:59:33 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Robert Hancock <hancockr@...w.ca>,
	Lee Howard <faxguy@...ardsilvan.com>,
	linux-serial@...r.kernel.org, tytso@....edu,
	linux-kernel@...r.kernel.org
Subject: Re: serial flow control appears broken

On Mon, Jul 30, 2007 at 10:45:19AM +0100, Maciej W. Rozycki wrote:
> On Sat, 28 Jul 2007, Russell King wrote:
> 
> > Essentially, any complex interrupt handler (such as an IDE interrupt
> > doing a multi-sector PIO transfer _in interrupt context_) can cause this
> > kind of starvation.  That's why Linux 1.x had bottom halves - so that
> > the time consuming work could be moved out of the interrupt handler,
> > thereby causing minimal the blockage of other interrupts.
> > 
> > Unfortunately, that kind of design has been long since forgotten.
> > Apparantly modern machines are fast enough that it doesn't have to be
> > worried about anymore...  Or are they?
> 
>  I would guess it is not that the machines are fast enough, but that this 
> two-level processing makes things more complicated.  Enough that most 
> people would not bother digging into it unless really forced.  Only 
> occasional latency problems are probably not enough of a force.

It's a shame we don't have a way to measure IRQ latency - it would be
very useful to flag up problems.

I think the best we could do is to arrange for the timer interrupt to
complain if it's delayed by more than 1ms or so - but some architectures
already run their timers with IRQF_DISABLED as a work around some of
the latency issues.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
-
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/