linux-kernel - Re: [PATCH 1/2] irq_flags_t: intro and core annotations

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Date:	Mon, 22 Oct 2007 16:47:16 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthew Wilcox <matthew@....cx>, Arnd Bergmann <arnd@...db.de>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Al Viro <viro@....linux.org.uk>, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/2] irq_flags_t: intro and core annotations

Andrew Morton wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:

>> > On Mon, 22 Oct 2007, Matthew Wilcox wrote:
>>> > > We certainly don't want to encourage people to blindly make those
>>> > > conversions ... and I've seen the results of encouraging kernel janitors
>>> > > to do things a certain way.

>> > There's another issue: the "irqsave/irqrestore" versions are much safer 
>> > than the plain "irq" versions, in case the caller already has interrupts 
>> > disabled. 

> It's almost always a bug to do spin_lock_irq() when local interrupts are
> disabled.


Let me add to the chorus of voices:  I continually see two cases where 
real bugs crop up:

1) hacker uses spin_lock_irq() in incorrect context (where it is not 
safe to do a blind enable/disable)

2) hacker uses spin_lock_irq() correctly, but the surrounding code 
changes, thus invalidating prior assumptions.

I would even go so far as to support the drastic measure of deleting 
spin_lock_irq().

spin_lock_irqsave() generates fewer bugs, is more future-proof, and by 
virtue of 'flags' permits architectures a bit more flexibility.

	Jeff



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