linux-kernel - Re: [PATCH 10/10] oom: Make find_lock_task

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Message-ID: <20120324162151.GA3640@lizard>
Date:	Sat, 24 Mar 2012 20:21:52 +0400
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Russell King <linux@....linux.org.uk>,
	Mike Frysinger <vapier@...too.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Richard Weinberger <richard@....at>,
	Paul Mundt <lethal@...ux-sh.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	John Stultz <john.stultz@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linuxppc-dev@...ts.ozlabs.org, linux-sh@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net, linux-mm@...ck.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 10/10] oom: Make find_lock_task_mm() sparse-aware

On Sat, Mar 24, 2012 at 01:52:54PM +0100, Peter Zijlstra wrote:
[...]
> > p.s. I know Peter Zijlstra detest the __cond_lock() stuff, but untill
> >      we have anything better in sparse, let's use it. This particular
> >      patch helped me to detect one bug that I myself made during
> >      task->mm fixup series. So, it is useful.
> 
> Yeah, so Nacked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> 
> Also, why didn't lockdep catch it?

Because patch authors test their patches on architectures they own
(well, sometimes I do check patches on exotic architectures w/ qemu,
but it is less convenient than just build/sparse-test the patch w/
a cross compiler).

And since lockdep is a runtime checker, it is not very useful.

Sparse is a build-time checker, so it is even better in the sense
that it is able to catch bugs even in code that is executed rarely.

> Fix sparse already instead of smearing ugly all over.

Just wonder how do you see the feature implemented?

Something like this?

#define __ret_cond_locked(l, c)	__attribute__((ret_cond_locked(l, c)))
#define __ret_value		__attribute__((ret_value))
#define __ret_locked_nonnull(l)	__ret_cond_locked(l, __ret_value);

extern struct task_struct *find_lock_task_mm(struct task_struct *p)
	__ret_locked_nonnull(&__ret_value->alloc_lock);

Thanks,

-- 
Anton Vorontsov
Email: cbouatmailru@...il.com
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