linux-kernel - Re: [patch 1/2] spinlocks: check spinlock_t/rwlock

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Date:	Mon, 21 Sep 2009 21:30:34 +0100
From:	Dave <kilroyd@...glemail.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...e.hu>, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] spinlocks: check spinlock_t/rwlock_t argument type
 on non-SMP builds

Andrew Morton wrote:
> On Mon, 21 Sep 2009 09:43:52 +0200
> Ingo Molnar <mingo@...e.hu> wrote:
> 
>> * akpm@...ux-foundation.org <akpm@...ux-foundation.org> wrote:
>>
>>> From: David Kilroy <kilroyd@...glemail.com>
>>>
>>> When writing code for UP without CONFIG_DEBUG_SPINLOCK it's easy to get
>>> the first argument to the spinlock/rwlock functions wrong.  This is
>>> because the parameter is not actually used in this configuration.
>>>
>>> Typically you will only find out it's wrong
>>>  * by rebuilding with CONFIG_SMP or CONFIG_DEBUG_SPINLOCK
>>>  * after you've submitted your beautiful patch series.
>>>
>>> The first means a long wait, and the latter is a bit late.
>>>
>>> Change the intermediate macros into inline functions.
>>>
>>> Signed-off-by: David Kilroy <kilroyd@...glemail.com>
>>> Cc: Ingo Molnar <mingo@...e.hu>
>>> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>>> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>>> ---
>>>
>>>  include/linux/spinlock.h        |    6 -
>>>  include/linux/spinlock_api_up.h |  118 ++++++++++++++++++++++--------
>>>  2 files changed, 92 insertions(+), 32 deletions(-)
>>>
>>> diff -puN include/linux/spinlock.h~spinlocks-check-spinlock_t-rwlock_t-argument-type-on-non-smp-builds include/linux/spinlock.h
>>> --- a/include/linux/spinlock.h~spinlocks-check-spinlock_t-rwlock_t-argument-type-on-non-smp-builds
>>> +++ a/include/linux/spinlock.h
>>> @@ -240,17 +240,17 @@ static inline void smp_mb__after_lock(vo
>>>  #define spin_lock_irqsave(lock, flags)			\
>>>  	do {						\
>>>  		typecheck(unsigned long, flags);	\
>>> -		_spin_lock_irqsave(lock, flags);	\
>>> +		_spin_lock_irqsave(lock, &flags);	\
>>>  	} while (0)
>>>  #define read_lock_irqsave(lock, flags)			\
>>>  	do {						\
>>>  		typecheck(unsigned long, flags);	\
>>> -		_read_lock_irqsave(lock, flags);	\
>>> +		_read_lock_irqsave(lock, &flags);	\
>>>  	} while (0)
>> these bits broke the Alpha build:
>>
>> /home/mingo/tip/arch/alpha/include/asm/core_t2.h: In function 't2_readb':
>> /home/mingo/tip/arch/alpha/include/asm/core_t2.h:451: error: '_spin_lock_irqsave' is static but used in inline function 't2_readb' which is not static
> 
> hm.  What the heck does that mean?
> 
> __EXTERN_INLINE u8 t2_readb(const volatile void __iomem *xaddr)
> 
> Something to do with the extern-inline?

This came up the last time this went into Ingos tree. And yes, it's the
extern inlines using the spinlock functions that causes the error.

> Do you have the .config?  My alpha builds went OK.

Last I checked, you need to have:
CONFIG_SMP=N
CONFIG_DEBUG_SPINLOCK=N

The latter gets auto-selected, so I set:
CONFIG_DEBUG_LOCK_ALLOC=N
CONFIG_LOCK_STAT=N
CONFIG_PROVE_LOCKING=N
CONFIG_LOCK_STAT=N


Regards,

Dave.
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