[RFC][PATCH] futex: Hide false positive about uninit var usage

[RFC][PATCH] futex: Hide false positive about uninit var usage

[Sergio Aguirre]

In exit_robust_list, there was this warning shown:

kernel/futex.c: In function 'exit_robust_list':
kernel/futex.c:2492: warning: 'next_pi' may be used uninitialized in this function

Which is a false positive, since in the function, the only scenario
possible in which the var is read, is after a successful excecution of
fetch_robust_entry, which populates the variable.

So there's no real possibility of it being used uninitialized.

Signed-off-by: Sergio Aguirre <saaguirre@ti.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@gmail.com>
---
 kernel/futex.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 6c683b3..3646157 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2489,7 +2489,8 @@ void exit_robust_list(struct task_struct *curr)
 {
 	struct robust_list_head __user *head = curr->robust_list;
 	struct robust_list __user *entry, *next_entry, *pending;
-	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
+	unsigned int limit = ROBUST_LIST_LIMIT, pi;
+	unsigned int uninitialized_var(next_pi), pip;
 	unsigned long futex_offset;
 	int rc;
 
-- 
1.7.0.4

Re: [RFC][PATCH] futex: Hide false positive about uninit var usage

[Darren Hart]

On 11/16/2010 08:32 AM, Sergio Aguirre wrote:
> In exit_robust_list, there was this warning shown:
>
> kernel/futex.c: In function 'exit_robust_list':
> kernel/futex.c:2492: warning: 'next_pi' may be used uninitialized in this function
>
> Which is a false positive, since in the function, the only scenario
> possible in which the var is read, is after a successful excecution of
> fetch_robust_entry, which populates the variable.
>
> So there's no real possibility of it being used uninitialized.

Hi Sergio,

You are correct. Thomas has recently pulled my fix for this into tip, it 
should be queued for mainline already.

Thanks,

Darren Hart

>
> Signed-off-by: Sergio Aguirre<saaguirre@ti.com>
> Cc: Thomas Gleixner<tglx@linutronix.de>
> Cc: Peter Zijlstra<a.p.zijlstra@chello.nl>
> Cc: Darren Hart<dvhart@linux.intel.com>
> Cc: Ingo Molnar<mingo@elte.hu>
> Cc: Namhyung Kim<namhyung@gmail.com>
> ---
>   kernel/futex.c |    3 ++-
>   1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 6c683b3..3646157 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -2489,7 +2489,8 @@ void exit_robust_list(struct task_struct *curr)
>   {
>   	struct robust_list_head __user *head = curr->robust_list;
>   	struct robust_list __user *entry, *next_entry, *pending;
> -	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
> +	unsigned int limit = ROBUST_LIST_LIMIT, pi;
> +	unsigned int uninitialized_var(next_pi), pip;
>   	unsigned long futex_offset;
>   	int rc;
>


-- 
Darren Hart
Yocto Linux Kernel

RE: [RFC][PATCH] futex: Hide false positive about uninit var usage

[Aguirre, Sergio]

Hi Darren,

> -----Original Message-----
> From: Darren Hart [mailto:dvhart@linux.intel.com]
> Sent: Tuesday, November 16, 2010 10:43 AM
> To: Aguirre, Sergio
> Cc: LKML; Thomas Gleixner; Peter Zijlstra; Ingo Molnar; Namhyung Kim
> Subject: Re: [RFC][PATCH] futex: Hide false positive about uninit var
> usage
> 
> On 11/16/2010 08:32 AM, Sergio Aguirre wrote:
> > In exit_robust_list, there was this warning shown:
> >
> > kernel/futex.c: In function 'exit_robust_list':
> > kernel/futex.c:2492: warning: 'next_pi' may be used uninitialized in
> this function
> >
> > Which is a false positive, since in the function, the only scenario
> > possible in which the var is read, is after a successful excecution of
> > fetch_robust_entry, which populates the variable.
> >
> > So there's no real possibility of it being used uninitialized.
> 
> Hi Sergio,
> 
> You are correct. Thomas has recently pulled my fix for this into tip, it
> should be queued for mainline already.

Oh ok. Sorry, I didn't know that. Please ignore this patch then.

Regards,
Sergio

> 
> Thanks,
> 
> Darren Hart
> 
> >
> > Signed-off-by: Sergio Aguirre<saaguirre@ti.com>
> > Cc: Thomas Gleixner<tglx@linutronix.de>
> > Cc: Peter Zijlstra<a.p.zijlstra@chello.nl>
> > Cc: Darren Hart<dvhart@linux.intel.com>
> > Cc: Ingo Molnar<mingo@elte.hu>
> > Cc: Namhyung Kim<namhyung@gmail.com>
> > ---
> >   kernel/futex.c |    3 ++-
> >   1 files changed, 2 insertions(+), 1 deletions(-)
> >
> > diff --git a/kernel/futex.c b/kernel/futex.c
> > index 6c683b3..3646157 100644
> > --- a/kernel/futex.c
> > +++ b/kernel/futex.c
> > @@ -2489,7 +2489,8 @@ void exit_robust_list(struct task_struct *curr)
> >   {
> >   	struct robust_list_head __user *head = curr->robust_list;
> >   	struct robust_list __user *entry, *next_entry, *pending;
> > -	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
> > +	unsigned int limit = ROBUST_LIST_LIMIT, pi;
> > +	unsigned int uninitialized_var(next_pi), pip;
> >   	unsigned long futex_offset;
> >   	int rc;
> >
> 
> 
> --
> Darren Hart
> Yocto Linux Kernel

Re: [RFC][PATCH] futex: Hide false positive about uninit var usage

[Darren Hart]

On 11/16/2010 08:59 AM, Aguirre, Sergio wrote:
> Hi Darren,
>
>> -----Original Message-----
>> From: Darren Hart [mailto:dvhart@linux.intel.com]
>> Sent: Tuesday, November 16, 2010 10:43 AM
>> To: Aguirre, Sergio
>> Cc: LKML; Thomas Gleixner; Peter Zijlstra; Ingo Molnar; Namhyung Kim
>> Subject: Re: [RFC][PATCH] futex: Hide false positive about uninit var
>> usage
>>
>> On 11/16/2010 08:32 AM, Sergio Aguirre wrote:
>>> In exit_robust_list, there was this warning shown:
>>>
>>> kernel/futex.c: In function 'exit_robust_list':
>>> kernel/futex.c:2492: warning: 'next_pi' may be used uninitialized in
>> this function
>>>
>>> Which is a false positive, since in the function, the only scenario
>>> possible in which the var is read, is after a successful excecution of
>>> fetch_robust_entry, which populates the variable.
>>>
>>> So there's no real possibility of it being used uninitialized.
>>
>> Hi Sergio,
>>
>> You are correct. Thomas has recently pulled my fix for this into tip, it
>> should be queued for mainline already.
>
> Oh ok. Sorry, I didn't know that. Please ignore this patch then.

No problem. In the future, if you run into problems with futexes, check 
the linux-2.6-tip repository for fixes as that is where they are queued 
up before going into mainline.

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git
branch: core/futexes

Thanks,

Darren

>
> Regards,
> Sergio
>
>>
>> Thanks,
>>
>> Darren Hart
>>
>>>
>>> Signed-off-by: Sergio Aguirre<saaguirre@ti.com>
>>> Cc: Thomas Gleixner<tglx@linutronix.de>
>>> Cc: Peter Zijlstra<a.p.zijlstra@chello.nl>
>>> Cc: Darren Hart<dvhart@linux.intel.com>
>>> Cc: Ingo Molnar<mingo@elte.hu>
>>> Cc: Namhyung Kim<namhyung@gmail.com>
>>> ---
>>>    kernel/futex.c |    3 ++-
>>>    1 files changed, 2 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/kernel/futex.c b/kernel/futex.c
>>> index 6c683b3..3646157 100644
>>> --- a/kernel/futex.c
>>> +++ b/kernel/futex.c
>>> @@ -2489,7 +2489,8 @@ void exit_robust_list(struct task_struct *curr)
>>>    {
>>>    	struct robust_list_head __user *head = curr->robust_list;
>>>    	struct robust_list __user *entry, *next_entry, *pending;
>>> -	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
>>> +	unsigned int limit = ROBUST_LIST_LIMIT, pi;
>>> +	unsigned int uninitialized_var(next_pi), pip;
>>>    	unsigned long futex_offset;
>>>    	int rc;
>>>
>>
>>
>> --
>> Darren Hart
>> Yocto Linux Kernel


-- 
Darren Hart
Yocto Linux Kernel