diff mbox

[6/8] i2c:i2c_core Fix warning: variable 'dummy' set but not used

Message ID 1276547208-26569-7-git-send-email-justinmattock@gmail.com (mailing list archive)
State Superseded, archived
Headers

Commit Message

Justin P. Mattock June 14, 2010, 8:26 p.m. UTC 
  could be a right solution, could be wrong
here is the warning:
  CC      drivers/i2c/i2c-core.o
drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
 
 Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>

---
 drivers/i2c/i2c-core.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

Comments

Jean Delvare June 14, 2010, 8:53 p.m. UTC | #1 
Hi Justin,

On Mon, 14 Jun 2010 13:26:46 -0700, Justin P. Mattock wrote:
> could be a right solution, could be wrong
> here is the warning:
>   CC      drivers/i2c/i2c-core.o
> drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
> drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
>  
>  Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
> 
> ---
>  drivers/i2c/i2c-core.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index 1cca263..79c6c26 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -794,6 +794,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
>  	mutex_lock(&core_lock);
>  	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
>  				 __process_new_adapter);
> +	if(!dummy)
> +		dummy = 0;

One word: scripts/checkpatch.pl

In other news, the above is just plain wrong. First we force people to
read the result of bus_for_each_drv() and then when they do and don't
need the value, gcc complains, so we add one more layer of useless
code, which developers and possibly tools will later wonder and
complain about? I can easily imagine that a static code analyzer would
spot the above code as being a potential bug.

Let's stop this madness now please.

Either __must_check goes away from bus_for_each_drv() and from every
other function which raises this problem, or we must disable that new
type of warning gcc 4.6.0 generates. Depends which warnings we value
more, as we can't sanely have both.

>  	mutex_unlock(&core_lock);
>  
>  	return 0;
Justin P. Mattock June 14, 2010, 9:06 p.m. UTC | #2 
On 06/14/2010 01:53 PM, Jean Delvare wrote:
> Hi Justin,
>
> On Mon, 14 Jun 2010 13:26:46 -0700, Justin P. Mattock wrote:
>> could be a right solution, could be wrong
>> here is the warning:
>>    CC      drivers/i2c/i2c-core.o
>> drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
>> drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
>>
>>   Signed-off-by: Justin P. Mattock<justinmattock@gmail.com>
>>
>> ---
>>   drivers/i2c/i2c-core.c |    2 ++
>>   1 files changed, 2 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
>> index 1cca263..79c6c26 100644
>> --- a/drivers/i2c/i2c-core.c
>> +++ b/drivers/i2c/i2c-core.c
>> @@ -794,6 +794,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
>>   	mutex_lock(&core_lock);
>>   	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
>>   				 __process_new_adapter);
>> +	if(!dummy)
>> +		dummy = 0;
>
> One word: scripts/checkpatch.pl

it was this, and/or just take the code out
(since I'm a newbie)

>
> In other news, the above is just plain wrong. First we force people to
> read the result of bus_for_each_drv() and then when they do and don't
> need the value, gcc complains, so we add one more layer of useless
> code, which developers and possibly tools will later wonder and
> complain about? I can easily imagine that a static code analyzer would
> spot the above code as being a potential bug.
>
> Let's stop this madness now please.
>

your telling me!! I haven't even compiled all the way
through the kernel yet.(lots of warnings)

> Either __must_check goes away from bus_for_each_drv() and from every
> other function which raises this problem, or we must disable that new
> type of warning gcc 4.6.0 generates. Depends which warnings we value
> more, as we can't sanely have both.
>
>>   	mutex_unlock(&core_lock);
>>
>>   	return 0;
>
>

up to you guys..
best thing now is deciphering what
and what not is an actual issue.

Justin P. Mattock
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David Daney June 14, 2010, 9:28 p.m. UTC | #3 
On 06/14/2010 01:53 PM, Jean Delvare wrote:
> Hi Justin,
>
> On Mon, 14 Jun 2010 13:26:46 -0700, Justin P. Mattock wrote:
>> could be a right solution, could be wrong
>> here is the warning:
>>    CC      drivers/i2c/i2c-core.o
>> drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
>> drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
>>
>>   Signed-off-by: Justin P. Mattock<justinmattock@gmail.com>
>>
>> ---
>>   drivers/i2c/i2c-core.c |    2 ++
>>   1 files changed, 2 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
>> index 1cca263..79c6c26 100644
>> --- a/drivers/i2c/i2c-core.c
>> +++ b/drivers/i2c/i2c-core.c
>> @@ -794,6 +794,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
>>   	mutex_lock(&core_lock);
>>   	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
>>   				 __process_new_adapter);
>> +	if(!dummy)
>> +		dummy = 0;
>
> One word: scripts/checkpatch.pl
>
> In other news, the above is just plain wrong. First we force people to
> read the result of bus_for_each_drv() and then when they do and don't
> need the value, gcc complains, so we add one more layer of useless
> code, which developers and possibly tools will later wonder and
> complain about? I can easily imagine that a static code analyzer would
> spot the above code as being a potential bug.
>
> Let's stop this madness now please.
>
> Either __must_check goes away from bus_for_each_drv() and from every
> other function which raises this problem, or we must disable that new
> type of warning gcc 4.6.0 generates. Depends which warnings we value
> more, as we can't sanely have both.
>

That is the crux of the whole thing.  Putting in crap to get rid of the 
__must_check warning someone obviously wanted to provoke is just plain 
wrong.

I don't know what the answer is, but in addition to your suggestion of 
removing the __must_check, you might try:

BUG_ON(dummy != WHAT_IT_SHOULD_BE);

or

if (dummy != WHAT_IT_SHOULD_BE)
	panic("nice message here);


or

static inline void i_really_know_what_i_am_doing(int arg)
{
	/*
	 * Trick the compiler because we don't want to
	 * handle error conditions.
	 */
	return;
}

.
.
.

	i_really_know_what_i_am_doing(dummy);



David Daney

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Jean Delvare June 15, 2010, 11:40 a.m. UTC | #4 
Hi David,

On Mon, 14 Jun 2010 14:28:57 -0700, David Daney wrote:
> On 06/14/2010 01:53 PM, Jean Delvare wrote:
> > Hi Justin,
> >
> > On Mon, 14 Jun 2010 13:26:46 -0700, Justin P. Mattock wrote:
> >> could be a right solution, could be wrong
> >> here is the warning:
> >>    CC      drivers/i2c/i2c-core.o
> >> drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
> >> drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
> >>
> >>   Signed-off-by: Justin P. Mattock<justinmattock@gmail.com>
> >>
> >> ---
> >>   drivers/i2c/i2c-core.c |    2 ++
> >>   1 files changed, 2 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> >> index 1cca263..79c6c26 100644
> >> --- a/drivers/i2c/i2c-core.c
> >> +++ b/drivers/i2c/i2c-core.c
> >> @@ -794,6 +794,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
> >>   	mutex_lock(&core_lock);
> >>   	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
> >>   				 __process_new_adapter);
> >> +	if(!dummy)
> >> +		dummy = 0;
> >
> > One word: scripts/checkpatch.pl
> >
> > In other news, the above is just plain wrong. First we force people to
> > read the result of bus_for_each_drv() and then when they do and don't
> > need the value, gcc complains, so we add one more layer of useless
> > code, which developers and possibly tools will later wonder and
> > complain about? I can easily imagine that a static code analyzer would
> > spot the above code as being a potential bug.
> >
> > Let's stop this madness now please.
> >
> > Either __must_check goes away from bus_for_each_drv() and from every
> > other function which raises this problem, or we must disable that new
> > type of warning gcc 4.6.0 generates. Depends which warnings we value
> > more, as we can't sanely have both.
> >
> 
> That is the crux of the whole thing.  Putting in crap to get rid of the 
> __must_check warning someone obviously wanted to provoke is just plain 
> wrong.

__process_new_adapter() calls i2c_do_add_adapter() which always returns
0. Why should I check the return value of bus_for_each_drv() when I
know it will always be 0 by construction?

Also note that the same function is also called through
bus_for_each_dev() somewhere else in i2c-core, and there is no warning
there because bus_for_each_dev() is not marked __must_check. How
consistent is this? If bus_for_each_dev() is OK without __must_check,
then I can't see why bus_for_each_drv() wouldn't be.

> I don't know what the answer is, but in addition to your suggestion of 
> removing the __must_check, you might try:
> 
> BUG_ON(dummy != WHAT_IT_SHOULD_BE);
> 
> or
> 
> if (dummy != WHAT_IT_SHOULD_BE)
> 	panic("nice message here);

Which will never trigger.

> or
> 
> static inline void i_really_know_what_i_am_doing(int arg)
> {
> 	/*
> 	 * Trick the compiler because we don't want to
> 	 * handle error conditions.
> 	 */
> 	return;
> }
> 
> ..
> ..
> ..
> 
> 	i_really_know_what_i_am_doing(dummy);

Which is adding a lot of lines, and might eventually fail when the
compiler becomes smarter (if it isn't already). Thanks but no thanks.
If I really have to chose one of these evils, I'll go for BUG_ON(), at
least the intent is clear and the bloat is minimum.
Jean Delvare June 15, 2010, 11:43 a.m. UTC | #5 
Hi Justin,

On Mon, 14 Jun 2010 14:06:12 -0700, Justin P. Mattock wrote:
> On 06/14/2010 01:53 PM, Jean Delvare wrote:
> > Hi Justin,
> >
> > On Mon, 14 Jun 2010 13:26:46 -0700, Justin P. Mattock wrote:
> >> could be a right solution, could be wrong
> >> here is the warning:
> >>    CC      drivers/i2c/i2c-core.o
> >> drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
> >> drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
> >>
> >>   Signed-off-by: Justin P. Mattock<justinmattock@gmail.com>
> >>
> >> ---
> >>   drivers/i2c/i2c-core.c |    2 ++
> >>   1 files changed, 2 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> >> index 1cca263..79c6c26 100644
> >> --- a/drivers/i2c/i2c-core.c
> >> +++ b/drivers/i2c/i2c-core.c
> >> @@ -794,6 +794,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
> >>   	mutex_lock(&core_lock);
> >>   	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
> >>   				 __process_new_adapter);
> >> +	if(!dummy)
> >> +		dummy = 0;
> >
> > One word: scripts/checkpatch.pl
> 
> it was this, and/or just take the code out
> (since I'm a newbie)

I was not (yet) arguing on the code itself, but on its format. Any
patch you send should pass the formatting tests performed by
scripts/checkpatch.pl. Thanks.
David Daney June 15, 2010, 4:20 p.m. UTC | #6 
On 06/15/2010 04:40 AM, Jean Delvare wrote:
> Hi David,
>
> On Mon, 14 Jun 2010 14:28:57 -0700, David Daney wrote:
>> On 06/14/2010 01:53 PM, Jean Delvare wrote:
>>> Hi Justin,
>>>
>>> On Mon, 14 Jun 2010 13:26:46 -0700, Justin P. Mattock wrote:
>>>> could be a right solution, could be wrong
>>>> here is the warning:
>>>>     CC      drivers/i2c/i2c-core.o
>>>> drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
>>>> drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
>>>>
>>>>    Signed-off-by: Justin P. Mattock<justinmattock@gmail.com>
>>>>
>>>> ---
>>>>    drivers/i2c/i2c-core.c |    2 ++
>>>>    1 files changed, 2 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
>>>> index 1cca263..79c6c26 100644
>>>> --- a/drivers/i2c/i2c-core.c
>>>> +++ b/drivers/i2c/i2c-core.c
>>>> @@ -794,6 +794,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
>>>>    	mutex_lock(&core_lock);
>>>>    	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
>>>>    				 __process_new_adapter);
>>>> +	if(!dummy)
>>>> +		dummy = 0;
>>>
>>> One word: scripts/checkpatch.pl
>>>
>>> In other news, the above is just plain wrong. First we force people to
>>> read the result of bus_for_each_drv() and then when they do and don't
>>> need the value, gcc complains, so we add one more layer of useless
>>> code, which developers and possibly tools will later wonder and
>>> complain about? I can easily imagine that a static code analyzer would
>>> spot the above code as being a potential bug.
>>>
>>> Let's stop this madness now please.
>>>
>>> Either __must_check goes away from bus_for_each_drv() and from every
>>> other function which raises this problem, or we must disable that new
>>> type of warning gcc 4.6.0 generates. Depends which warnings we value
>>> more, as we can't sanely have both.
>>>
>>
>> That is the crux of the whole thing.  Putting in crap to get rid of the
>> __must_check warning someone obviously wanted to provoke is just plain
>> wrong.
>
> __process_new_adapter() calls i2c_do_add_adapter() which always returns
> 0. Why should I check the return value of bus_for_each_drv() when I
> know it will always be 0 by construction?
>
> Also note that the same function is also called through
> bus_for_each_dev() somewhere else in i2c-core, and there is no warning
> there because bus_for_each_dev() is not marked __must_check. How
> consistent is this? If bus_for_each_dev() is OK without __must_check,
> then I can't see why bus_for_each_drv() wouldn't be.
>

Well, I would advocate removing the __must_check then.


David Daney
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Justin P. Mattock June 15, 2010, 4:51 p.m. UTC | #7 
On 06/15/2010 04:43 AM, Jean Delvare wrote:
> Hi Justin,
>
> On Mon, 14 Jun 2010 14:06:12 -0700, Justin P. Mattock wrote:
>> On 06/14/2010 01:53 PM, Jean Delvare wrote:
>>> Hi Justin,
>>>
>>> On Mon, 14 Jun 2010 13:26:46 -0700, Justin P. Mattock wrote:
>>>> could be a right solution, could be wrong
>>>> here is the warning:
>>>>     CC      drivers/i2c/i2c-core.o
>>>> drivers/i2c/i2c-core.c: In function 'i2c_register_adapter':
>>>> drivers/i2c/i2c-core.c:757:15: warning: variable 'dummy' set but not used
>>>>
>>>>    Signed-off-by: Justin P. Mattock<justinmattock@gmail.com>
>>>>
>>>> ---
>>>>    drivers/i2c/i2c-core.c |    2 ++
>>>>    1 files changed, 2 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
>>>> index 1cca263..79c6c26 100644
>>>> --- a/drivers/i2c/i2c-core.c
>>>> +++ b/drivers/i2c/i2c-core.c
>>>> @@ -794,6 +794,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
>>>>    	mutex_lock(&core_lock);
>>>>    	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
>>>>    				 __process_new_adapter);
>>>> +	if(!dummy)
>>>> +		dummy = 0;
>>>
>>> One word: scripts/checkpatch.pl
>>
>> it was this, and/or just take the code out
>> (since I'm a newbie)
>
> I was not (yet) arguing on the code itself, but on its format. Any
> patch you send should pass the formatting tests performed by
> scripts/checkpatch.pl. Thanks.
>


o.k.  I'll make sure I run everything through checkpatch.pl before 
sending anything.

Justin P. Mattock
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Jean Delvare June 16, 2010, 9:45 a.m. UTC | #8 
On Tue, 15 Jun 2010 09:20:39 -0700, David Daney wrote:
> On 06/15/2010 04:40 AM, Jean Delvare wrote:
> > __process_new_adapter() calls i2c_do_add_adapter() which always returns
> > 0. Why should I check the return value of bus_for_each_drv() when I
> > know it will always be 0 by construction?
> >
> > Also note that the same function is also called through
> > bus_for_each_dev() somewhere else in i2c-core, and there is no warning
> > there because bus_for_each_dev() is not marked __must_check. How
> > consistent is this? If bus_for_each_dev() is OK without __must_check,
> > then I can't see why bus_for_each_drv() wouldn't be.
> 
> Well, I would advocate removing the __must_check then.

I have just sent a patch to LKML doing exactly this.
diff mbox

Patch

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 1cca263..79c6c26 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -794,6 +794,8 @@  static int i2c_register_adapter(struct i2c_adapter *adap)
 	mutex_lock(&core_lock);
 	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
 				 __process_new_adapter);
+	if(!dummy)
+		dummy = 0;
 	mutex_unlock(&core_lock);
 
 	return 0;