[PATCH] ARM: EXYNOS: use BUG_ON where possible

[PATCH] ARM: EXYNOS: use BUG_ON where possible

[Sasha Levin]

Just use BUG_ON() instead of constructions such as:

	if (...)
		BUG()

A simplified version of the semantic patch that makes this transformation
is as follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression e;
@@
- if (e) BUG();
+ BUG_ON(e);
// </smpl>

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 arch/arm/mach-exynos/common.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mach-exynos/common.c b/arch/arm/mach-exynos/common.c
index 4e577f6..6a55a5a 100644
--- a/arch/arm/mach-exynos/common.c
+++ b/arch/arm/mach-exynos/common.c
@@ -465,10 +465,8 @@ static void __init combiner_cascade_irq(unsigned int combiner_nr, unsigned int i
 	else
 		max_nr = EXYNOS4_MAX_COMBINER_NR;
 
-	if (combiner_nr >= max_nr)
-		BUG();
-	if (irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0)
-		BUG();
+	BUG_ON(combiner_nr >= max_nr);
+	BUG_ON(irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0);
 	irq_set_chained_handler(irq, combiner_handle_cascade_irq);
 }
 
-- 
1.7.10.4

[PATCH] ARM: dma: use BUG_ON where possible

[Sasha Levin]

Just use BUG_ON() instead of constructions such as:

	if (...)
		BUG()

A simplified version of the semantic patch that makes this transformation
is as follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression e;
@@
- if (e) BUG();
+ BUG_ON(e);
// </smpl>

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 arch/arm/mach-rpc/dma.c     |    3 +--
 arch/arm/mach-s3c64xx/dma.c |    3 +--
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mach-rpc/dma.c b/arch/arm/mach-rpc/dma.c
index 85883b2..92e22ba 100644
--- a/arch/arm/mach-rpc/dma.c
+++ b/arch/arm/mach-rpc/dma.c
@@ -265,8 +265,7 @@ static void floppy_enable_dma(unsigned int chan, dma_t *dma)
 	unsigned int fiqhandler_length;
 	struct pt_regs regs;
 
-	if (fdma->dma.sg)
-		BUG();
+	BUG_ON(fdma->dma.sg);
 
 	if (fdma->dma.dma_mode == DMA_MODE_READ) {
 		extern unsigned char floppy_fiqin_start, floppy_fiqin_end;
diff --git a/arch/arm/mach-s3c64xx/dma.c b/arch/arm/mach-s3c64xx/dma.c
index f2a7a17..585c2ae 100644
--- a/arch/arm/mach-s3c64xx/dma.c
+++ b/arch/arm/mach-s3c64xx/dma.c
@@ -603,8 +603,7 @@ static irqreturn_t s3c64xx_dma_irq(int irq, void *pw)
 				&& buff->next != chan->next)
 			buff = buff->next;
 
-		if (!buff)
-			BUG();
+		BUG_ON(!buff);
 
 		if (buff == chan->next)
 			buff = chan->end;
-- 
1.7.10.4

Re: [PATCH] ARM: EXYNOS: use BUG_ON where possible

[Maarten Lankhorst]

Op 08-11-12 21:23, Sasha Levin schreef:
> Just use BUG_ON() instead of constructions such as:
>
> 	if (...)
> 		BUG()
>
> A simplified version of the semantic patch that makes this transformation
> is as follows: (http://coccinelle.lip6.fr/)
>
> // <smpl>
> @@
> expression e;
> @@
> - if (e) BUG();
> + BUG_ON(e);
> // </smpl>
>
> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
> ---
>  arch/arm/mach-exynos/common.c |    6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/mach-exynos/common.c b/arch/arm/mach-exynos/common.c
> index 4e577f6..6a55a5a 100644
> --- a/arch/arm/mach-exynos/common.c
> +++ b/arch/arm/mach-exynos/common.c
> @@ -465,10 +465,8 @@ static void __init combiner_cascade_irq(unsigned int combiner_nr, unsigned int i
>  	else
>  		max_nr = EXYNOS4_MAX_COMBINER_NR;
>  
> -	if (combiner_nr >= max_nr)
> -		BUG();
> -	if (irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0)
> -		BUG();
> +	BUG_ON(combiner_nr >= max_nr);
> +	BUG_ON(irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0);
Is it really a good idea to put functions that perform work in a BUG_ON?
I don't know, but for some reason it just feels wrong. I'd expect code to
compile fine if BUG_ON was a noop, so doing verification calls only, not
actual work..

~Maarten

Re: [PATCH] ARM: EXYNOS: use BUG_ON where possible

[Russell King - ARM Linux]

On Mon, Nov 12, 2012 at 04:12:29PM +0100, Maarten Lankhorst wrote:
> Op 08-11-12 21:23, Sasha Levin schreef:
> > @@ -465,10 +465,8 @@ static void __init combiner_cascade_irq(unsigned int combiner_nr, unsigned int i
> >  	else
> >  		max_nr = EXYNOS4_MAX_COMBINER_NR;
> >  
> > -	if (combiner_nr >= max_nr)
> > -		BUG();
> > -	if (irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0)
> > -		BUG();
> > +	BUG_ON(combiner_nr >= max_nr);
> > +	BUG_ON(irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0);
>
> Is it really a good idea to put functions that perform work in a BUG_ON?
> I don't know, but for some reason it just feels wrong. I'd expect code to
> compile fine if BUG_ON was a noop, so doing verification calls only, not
> actual work..

Well, it is currently defined as:

include/asm-generic/bug.h:#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while(0)
include/asm-generic/bug.h:#define BUG_ON(condition) do { if (condition) ; } while(0)

but as these can be overridden, I don't think relying on those
implementations is a good idea; to do so would be fragile.  Eg, what if
the BUG_ON() implementation becomes just:

#define BUG_ON(x)

then the function call itself vanishes.  So, only put the actual bug test
inside a BUG_ON(), not the functional part which must always be executed.

Re: [PATCH] ARM: EXYNOS: use BUG_ON where possible

[Sasha Levin]

On 11/12/2012 10:12 AM, Maarten Lankhorst wrote:
> Op 08-11-12 21:23, Sasha Levin schreef:
>> Just use BUG_ON() instead of constructions such as:
>>
>> 	if (...)
>> 		BUG()
>>
>> A simplified version of the semantic patch that makes this transformation
>> is as follows: (http://coccinelle.lip6.fr/)
>>
>> // <smpl>
>> @@
>> expression e;
>> @@
>> - if (e) BUG();
>> + BUG_ON(e);
>> // </smpl>
>>
>> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
>> ---
>>  arch/arm/mach-exynos/common.c |    6 ++----
>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/mach-exynos/common.c b/arch/arm/mach-exynos/common.c
>> index 4e577f6..6a55a5a 100644
>> --- a/arch/arm/mach-exynos/common.c
>> +++ b/arch/arm/mach-exynos/common.c
>> @@ -465,10 +465,8 @@ static void __init combiner_cascade_irq(unsigned int combiner_nr, unsigned int i
>>  	else
>>  		max_nr = EXYNOS4_MAX_COMBINER_NR;
>>  
>> -	if (combiner_nr >= max_nr)
>> -		BUG();
>> -	if (irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0)
>> -		BUG();
>> +	BUG_ON(combiner_nr >= max_nr);
>> +	BUG_ON(irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0);
> Is it really a good idea to put functions that perform work in a BUG_ON?
> I don't know, but for some reason it just feels wrong. I'd expect code to
> compile fine if BUG_ON was a noop, so doing verification calls only, not
> actual work..

You can't modify the side-effects of a macro based on kernel configuration. If
we're evaluating the expression when BUG_ON() is enabled, you must also evaluate
the expression when BUG_ON() is not enabled (HAVE_ARCH_BUG_ON is not set).

The only reason I'd not include function calls in a BUG_ON() call is due to
readability considerations. In this case it looked okay to me, but if someone
thinks that getting the function call into the BUG_ON() complicated things I'm
fine with skipping that.


Thanks,
Sasha

Re: [PATCH] ARM: EXYNOS: use BUG_ON where possible

[Sasha Levin]

On 11/12/2012 10:23 AM, Russell King - ARM Linux wrote:
> On Mon, Nov 12, 2012 at 04:12:29PM +0100, Maarten Lankhorst wrote:
>> Op 08-11-12 21:23, Sasha Levin schreef:
>>> @@ -465,10 +465,8 @@ static void __init combiner_cascade_irq(unsigned int combiner_nr, unsigned int i
>>>  	else
>>>  		max_nr = EXYNOS4_MAX_COMBINER_NR;
>>>  
>>> -	if (combiner_nr >= max_nr)
>>> -		BUG();
>>> -	if (irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0)
>>> -		BUG();
>>> +	BUG_ON(combiner_nr >= max_nr);
>>> +	BUG_ON(irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0);
>>
>> Is it really a good idea to put functions that perform work in a BUG_ON?
>> I don't know, but for some reason it just feels wrong. I'd expect code to
>> compile fine if BUG_ON was a noop, so doing verification calls only, not
>> actual work..
> 
> Well, it is currently defined as:
> 
> include/asm-generic/bug.h:#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while(0)
> include/asm-generic/bug.h:#define BUG_ON(condition) do { if (condition) ; } while(0)
> 
> but as these can be overridden, I don't think relying on those
> implementations is a good idea; to do so would be fragile.  Eg, what if
> the BUG_ON() implementation becomes just:
> 
> #define BUG_ON(x)
> 
> then the function call itself vanishes.  So, only put the actual bug test
> inside a BUG_ON(), not the functional part which must always be executed.

Even if we ignore that modifying the side-effects is wrong, there's already
more than enough code in the kernel (both in kernel/ / mm/, and in arch/) to
cause breakage if for some reason the expression is not evaluated.

If some arch decides to not evaluate the expression there it's going to be
inherently broken.


Thanks,
Sasha