linux-kernel - Re: start_kernel(): bug: interrupts were enabled early

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Message-ID: <20100331223039.GA8999@flint.arm.linux.org.uk>
Date:	Wed, 31 Mar 2010 23:30:40 +0100
From:	Russell King <rmk@....linux.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Matthew Wilcox <matthew@....cx>,
	Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rabin Vincent <rabin@....in>,
	lkml <linux-kernel@...r.kernel.org>, penberg@...helsinki.fi,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-arch@...r.kernel.org
Subject: Re: start_kernel(): bug: interrupts were enabled early

On Wed, Mar 31, 2010 at 02:57:20PM -0700, H. Peter Anvin wrote:
> On 03/31/2010 02:54 PM, Russell King wrote:
> > On Wed, Mar 31, 2010 at 04:42:25PM -0500, Christoph Lameter wrote:
> >> Do not run the checks while we are in a single threaded context?
> >>
> >> I thought we had some dynamic code patching thingamy that could change
> >> those when we go to smp mode?
> > 
> > You have to remember that on embedded architectures, such as ARM,
> > where XIP is supported we can't change the text segment at run time -
> > which means dynamic code patching won't work.
> > 
> > However, the kernel should still work in such situations.
> > 
> 
> The question still remains what the incremental cost is of doing
> irqsave/irqrestore.

Compared to irq disable/enable, it wouldn't be much higher; saving
can be done by a direct register to register move, so that should be
relatively cheap.  The restore may be a little bit more depending on
the CPU arch version, but not significant.

So there shouldn't be a problem from ARM POV to switch to using
irqsave/irqrestore.

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