linux-kernel - Re: [PATCH v2 2/6] oom: Get rid of sparse warnings

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Message-ID: <4F32BB5B.3010201@gmail.com>
Date:	Wed, 08 Feb 2012 13:13:47 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	San Mehat <san@...gle.com>, Colin Cross <ccross@...roid.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH v2 2/6] oom: Get rid of sparse warnings

(2/7/12 1:23 AM), Anton Vorontsov wrote:
> On Tue, Feb 07, 2012 at 12:38:58AM -0500, KOSAKI Motohiro wrote:
>>>> task struct only have allock_lock, not alloc_loc.
>>>
>>> Funnily, but sparse does not care. :-) __release(foo) will work as
>>> well. Seems like sparse counts locking balance globally.
>>>
>>> This is now fixed in the patch down below, thanks for catching.
>>>
>>>> Moreover we don't release
>>>> the lock in this code path. Seems odd.
>>>
>>> Indeed. That's exactly what sparse seeing is as well. We exit
>>> without releasing the lock, which is bad (in sparse' eyes). So
>>> we lie to sparse, telling it that we do release, so it shut ups.
>>
>> Hmmm....
>>
>> To be honest, I really dislike any lie annotation. Why? It is very
>> fragile and easily
>> become broken from unrelated but near line changes. Please consider to
>> enhance sparse at first.
>
> I somewhat doubt that it is possible to "enhance it". We keep the
> lock held conditionaly, so we need too place the hint in the
> code itself. I believe the best we can do would be something like
> this:
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 4a24354..61d91f2 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -14,6 +14,7 @@
>   # define __releases(x)	__attribute__((context(x,1,0)))
>   # define __acquire(x)	__context__(x,1)
>   # define __release(x)	__context__(x,-1)
> +# define __ret_with_lock(x)	__context__(x,-1)
>   # define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
>   # define __percpu	__attribute__((noderef, address_space(3)))
>   #ifdef CONFIG_SPARSE_RCU_POINTER
> @@ -37,6 +38,7 @@ extern void __chk_io_ptr(const volatile void __iomem *);
>   # define __releases(x)
>   # define __acquire(x) (void)0
>   # define __release(x) (void)0
> +# define __ret_with_lock(x)
>   # define __cond_lock(x,c) (c)
>   # define __percpu
>   # define __rcu
>
> And then use it instead of __release().

Hmmm...

I still dislike this lie annotation. But maybe it's better than nothing
(dunno, just guess). Go ahead.






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