Re: [PATCH 1/2] drivers: cpuidle: remove stale irq disabling call in cpuidle_enter_freeze()

[Rafael J. Wysocki]

On Thu, Feb 26, 2015 at 10:48 AM, Lorenzo Pieralisi
 wrote:
> On Wed, Feb 25, 2015 at 11:36:10PM +, Rafael J. Wysocki wrote:
>> On Wednesday, February 25, 2015 02:39:17 PM Lorenzo Pieralisi wrote:
>> > On Wed, Feb 25, 2015 at 02:13:23PM +, Daniel Lezcano wrote:

[cut]

>> I'm not entirely against of re-arranging things here, but a patch like the
>> (untested) one below might be more appropriate.
>>
>> Rafael (who would appreciate it if people asked questions instead of sending
>> patches on a hunch).
>
> I understand that, I wanted to just send [patch 2], this patch was more
> a way to get a clarification than anything else, asking would have been more
> appropriate, sorry.
>
> Anyway, I did not like disabling IRQs to just re-enable them on function
> return, in particular the comment below seemed to apply to the following
> line, which is a bit misleading.

I see.

>
> /* Interrupts are enabled again here. */
> local_irq_disable();
>
>>
>>
>> ---
>>  drivers/cpuidle/cpuidle.c |2 +-
>>  kernel/sched/idle.c   |1 -
>>  2 files changed, 1 insertion(+), 2 deletions(-)
>>
>> Index: linux-pm/drivers/cpuidle/cpuidle.c
>> ===
>> --- linux-pm.orig/drivers/cpuidle/cpuidle.c
>> +++ linux-pm/drivers/cpuidle/cpuidle.c
>> @@ -132,6 +132,7 @@ void cpuidle_enter_freeze(void)
>>   index = cpuidle_find_deepest_state(drv, dev, true);
>>   if (index >= 0) {
>>   enter_freeze_proper(drv, dev, index);
>> + local_irq_enable();
>>   return;
>>   }
>>
>> @@ -146,7 +147,6 @@ void cpuidle_enter_freeze(void)
>>   arch_cpu_idle();
>>
>>   /* Interrupts are enabled again here. */
>> - local_irq_disable();
>>  }
>>
>>  /**
>> Index: linux-pm/kernel/sched/idle.c
>> ===
>> --- linux-pm.orig/kernel/sched/idle.c
>> +++ linux-pm/kernel/sched/idle.c
>> @@ -116,7 +116,6 @@ static void cpuidle_idle_call(void)
>>*/
>>   if (idle_should_freeze()) {
>>   cpuidle_enter_freeze();
>> - local_irq_enable();
>>   goto exit_idle;
>>   }
>>
>
> It looks fine, I will test it. I would add a comment to
> cpuidle_enter_freeze() to document it must return with IRQs
> enabled.

OK

Rafael
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Re: [PATCH 1/2] drivers: cpuidle: remove stale irq disabling call in cpuidle_enter_freeze()

[Lorenzo Pieralisi]

On Wed, Feb 25, 2015 at 11:36:10PM +, Rafael J. Wysocki wrote:
> On Wednesday, February 25, 2015 02:39:17 PM Lorenzo Pieralisi wrote:
> > On Wed, Feb 25, 2015 at 02:13:23PM +, Daniel Lezcano wrote:
> > > On 02/24/2015 06:58 PM, Lorenzo Pieralisi wrote:
> > > > On return from cpuidle_enter_freeze() irqs are re-enabled by the 
> > > > function
> > > > caller (ie cpuidle_idle_call) in the idle loop. This patch removes a 
> > > > stale
> > > > local_irq_disable() call and its stale comment in 
> > > > cpuidle_enter_freeze(),
> > > > since they disagree and do not serve a useful purpose.
> > > >
> > > > Cc: Rafael J. Wysocki 
> > > > Cc: Daniel Lezcano 
> > > > Signed-off-by: Lorenzo Pieralisi 
> > > > ---
> > > >   drivers/cpuidle/cpuidle.c | 3 ---
> > > >   1 file changed, 3 deletions(-)
> > > >
> > > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> > > > index 4d53458..f47edc6c 100644
> > > > --- a/drivers/cpuidle/cpuidle.c
> > > > +++ b/drivers/cpuidle/cpuidle.c
> > > > @@ -144,9 +144,6 @@ void cpuidle_enter_freeze(void)
> > > > cpuidle_enter(drv, dev, index);
> > > > else
> > > > arch_cpu_idle();
> > > > -
> > > > -   /* Interrupts are enabled again here. */
> > > > -   local_irq_disable();
> > > >   }
> > > 
> > > Hmm, I think Rafael added this prevent lockdep to raise a warning.
> > 
> > Ok, so the comment is there to say "at this point of execution IRQs
> > are enabled", it does not refer to local_irq_disable() call effects,
> > that's misleading and not necessarily nice, at least it should
> > be explained.
> > 
> > > Otherwise, cpuidle_enter or arch_cpu_idle enables the irq again and then 
> > > when exiting the cpu_idle_call, we enable them again, so leading to a 
> > > lockdep WARN in trace_hardirqs_on_caller.
> > 
> > Would not it be better to enable irqs in cpuidle_enter_freeze() on
> > returning from enter_freeze_proper() and remove the local_irq_enable()
> > call in the cpuidle_idle_call() before jumping to exit_idle ?
> > 
> > > That said, if we have to do this, it may reveal something is wrong in 
> > > the code.
> > 
> > I just spotted code through inspection, I have to say at the moment it
> > is not very clear what it is meant to achieve, so I put together this
> > patch.
> 
> So there are two code paths in cpuidle_idle_call(), the enter_freeze_proper()
> one which does *not* re-enable interrupts and the one you modified which does
> that.  The local_irq_disable() is to keep things consistent.
> 
> I'm not entirely against of re-arranging things here, but a patch like the
> (untested) one below might be more appropriate.
> 
> Rafael (who would appreciate it if people asked questions instead of sending
> patches on a hunch).

I understand that, I wanted to just send [patch 2], this patch was more
a way to get a clarification than anything else, asking would have been more
appropriate, sorry.

Anyway, I did not like disabling IRQs to just re-enable them on function
return, in particular the comment below seemed to apply to the following
line, which is a bit misleading.

/* Interrupts are enabled again here. */
local_irq_disable();

> 
> 
> ---
>  drivers/cpuidle/cpuidle.c |2 +-
>  kernel/sched/idle.c   |1 -
>  2 files changed, 1 insertion(+), 2 deletions(-)
> 
> Index: linux-pm/drivers/cpuidle/cpuidle.c
> ===
> --- linux-pm.orig/drivers/cpuidle/cpuidle.c
> +++ linux-pm/drivers/cpuidle/cpuidle.c
> @@ -132,6 +132,7 @@ void cpuidle_enter_freeze(void)
>   index = cpuidle_find_deepest_state(drv, dev, true);
>   if (index >= 0) {
>   enter_freeze_proper(drv, dev, index);
> + local_irq_enable();
>   return;
>   }
>  
> @@ -146,7 +147,6 @@ void cpuidle_enter_freeze(void)
>   arch_cpu_idle();
>  
>   /* Interrupts are enabled again here. */
> - local_irq_disable();
>  }
>  
>  /**
> Index: linux-pm/kernel/sched/idle.c
> ===
> --- linux-pm.orig/kernel/sched/idle.c
> +++ linux-pm/kernel/sched/idle.c
> @@ -116,7 +116,6 @@ static void cpuidle_idle_call(void)
>*/
>   if (idle_should_freeze()) {
>   cpuidle_enter_freeze();
> - local_irq_enable();
>   goto exit_idle;
>   }
>  

It looks fine, I will test it. I would add a comment to
cpuidle_enter_freeze() to document it must return with IRQs
enabled.

Thanks,
Lorenzo
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Re: [PATCH 1/2] drivers: cpuidle: remove stale irq disabling call in cpuidle_enter_freeze()

[Rafael J. Wysocki]

On Wednesday, February 25, 2015 02:39:17 PM Lorenzo Pieralisi wrote:
> On Wed, Feb 25, 2015 at 02:13:23PM +, Daniel Lezcano wrote:
> > On 02/24/2015 06:58 PM, Lorenzo Pieralisi wrote:
> > > On return from cpuidle_enter_freeze() irqs are re-enabled by the function
> > > caller (ie cpuidle_idle_call) in the idle loop. This patch removes a stale
> > > local_irq_disable() call and its stale comment in cpuidle_enter_freeze(),
> > > since they disagree and do not serve a useful purpose.
> > >
> > > Cc: Rafael J. Wysocki 
> > > Cc: Daniel Lezcano 
> > > Signed-off-by: Lorenzo Pieralisi 
> > > ---
> > >   drivers/cpuidle/cpuidle.c | 3 ---
> > >   1 file changed, 3 deletions(-)
> > >
> > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> > > index 4d53458..f47edc6c 100644
> > > --- a/drivers/cpuidle/cpuidle.c
> > > +++ b/drivers/cpuidle/cpuidle.c
> > > @@ -144,9 +144,6 @@ void cpuidle_enter_freeze(void)
> > >   cpuidle_enter(drv, dev, index);
> > >   else
> > >   arch_cpu_idle();
> > > -
> > > - /* Interrupts are enabled again here. */
> > > - local_irq_disable();
> > >   }
> > 
> > Hmm, I think Rafael added this prevent lockdep to raise a warning.
> 
> Ok, so the comment is there to say "at this point of execution IRQs
> are enabled", it does not refer to local_irq_disable() call effects,
> that's misleading and not necessarily nice, at least it should
> be explained.
> 
> > Otherwise, cpuidle_enter or arch_cpu_idle enables the irq again and then 
> > when exiting the cpu_idle_call, we enable them again, so leading to a 
> > lockdep WARN in trace_hardirqs_on_caller.
> 
> Would not it be better to enable irqs in cpuidle_enter_freeze() on
> returning from enter_freeze_proper() and remove the local_irq_enable()
> call in the cpuidle_idle_call() before jumping to exit_idle ?
> 
> > That said, if we have to do this, it may reveal something is wrong in 
> > the code.
> 
> I just spotted code through inspection, I have to say at the moment it
> is not very clear what it is meant to achieve, so I put together this
> patch.

So there are two code paths in cpuidle_idle_call(), the enter_freeze_proper()
one which does *not* re-enable interrupts and the one you modified which does
that.  The local_irq_disable() is to keep things consistent.

I'm not entirely against of re-arranging things here, but a patch like the
(untested) one below might be more appropriate.

Rafael (who would appreciate it if people asked questions instead of sending
patches on a hunch).


---
 drivers/cpuidle/cpuidle.c |2 +-
 kernel/sched/idle.c   |1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

Index: linux-pm/drivers/cpuidle/cpuidle.c
===
--- linux-pm.orig/drivers/cpuidle/cpuidle.c
+++ linux-pm/drivers/cpuidle/cpuidle.c
@@ -132,6 +132,7 @@ void cpuidle_enter_freeze(void)
index = cpuidle_find_deepest_state(drv, dev, true);
if (index >= 0) {
enter_freeze_proper(drv, dev, index);
+   local_irq_enable();
return;
}
 
@@ -146,7 +147,6 @@ void cpuidle_enter_freeze(void)
arch_cpu_idle();
 
/* Interrupts are enabled again here. */
-   local_irq_disable();
 }
 
 /**
Index: linux-pm/kernel/sched/idle.c
===
--- linux-pm.orig/kernel/sched/idle.c
+++ linux-pm/kernel/sched/idle.c
@@ -116,7 +116,6 @@ static void cpuidle_idle_call(void)
 */
if (idle_should_freeze()) {
cpuidle_enter_freeze();
-   local_irq_enable();
goto exit_idle;
}
 

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Re: [PATCH 1/2] drivers: cpuidle: remove stale irq disabling call in cpuidle_enter_freeze()

[Lorenzo Pieralisi]

On Wed, Feb 25, 2015 at 02:13:23PM +, Daniel Lezcano wrote:
> On 02/24/2015 06:58 PM, Lorenzo Pieralisi wrote:
> > On return from cpuidle_enter_freeze() irqs are re-enabled by the function
> > caller (ie cpuidle_idle_call) in the idle loop. This patch removes a stale
> > local_irq_disable() call and its stale comment in cpuidle_enter_freeze(),
> > since they disagree and do not serve a useful purpose.
> >
> > Cc: Rafael J. Wysocki 
> > Cc: Daniel Lezcano 
> > Signed-off-by: Lorenzo Pieralisi 
> > ---
> >   drivers/cpuidle/cpuidle.c | 3 ---
> >   1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> > index 4d53458..f47edc6c 100644
> > --- a/drivers/cpuidle/cpuidle.c
> > +++ b/drivers/cpuidle/cpuidle.c
> > @@ -144,9 +144,6 @@ void cpuidle_enter_freeze(void)
> > cpuidle_enter(drv, dev, index);
> > else
> > arch_cpu_idle();
> > -
> > -   /* Interrupts are enabled again here. */
> > -   local_irq_disable();
> >   }
> 
> Hmm, I think Rafael added this prevent lockdep to raise a warning.

Ok, so the comment is there to say "at this point of execution IRQs
are enabled", it does not refer to local_irq_disable() call effects,
that's misleading and not necessarily nice, at least it should
be explained.

> Otherwise, cpuidle_enter or arch_cpu_idle enables the irq again and then 
> when exiting the cpu_idle_call, we enable them again, so leading to a 
> lockdep WARN in trace_hardirqs_on_caller.

Would not it be better to enable irqs in cpuidle_enter_freeze() on
returning from enter_freeze_proper() and remove the local_irq_enable()
call in the cpuidle_idle_call() before jumping to exit_idle ?

> That said, if we have to do this, it may reveal something is wrong in 
> the code.

I just spotted code through inspection, I have to say at the moment it
is not very clear what it is meant to achieve, so I put together this
patch.

Lorenzo
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Re: [PATCH 1/2] drivers: cpuidle: remove stale irq disabling call in cpuidle_enter_freeze()

[Daniel Lezcano]

On 02/24/2015 06:58 PM, Lorenzo Pieralisi wrote:

On return from cpuidle_enter_freeze() irqs are re-enabled by the function
caller (ie cpuidle_idle_call) in the idle loop. This patch removes a stale
local_irq_disable() call and its stale comment in cpuidle_enter_freeze(),
since they disagree and do not serve a useful purpose.

Cc: Rafael J. Wysocki 
Cc: Daniel Lezcano 
Signed-off-by: Lorenzo Pieralisi 
---
  drivers/cpuidle/cpuidle.c | 3 ---
  1 file changed, 3 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 4d53458..f47edc6c 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -144,9 +144,6 @@ void cpuidle_enter_freeze(void)
cpuidle_enter(drv, dev, index);
else
arch_cpu_idle();
-
-   /* Interrupts are enabled again here. */
-   local_irq_disable();
  }


Hmm, I think Rafael added this prevent lockdep to raise a warning.

Otherwise, cpuidle_enter or arch_cpu_idle enables the irq again and then 
when exiting the cpu_idle_call, we enable them again, so leading to a 
lockdep WARN in trace_hardirqs_on_caller.


That said, if we have to do this, it may reveal something is wrong in 
the code.



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