[PATCH] ARM: MCPM: don't explode if invoked without being initialized first

[Nicolas Pitre]

On Tue, 24 Sep 2013, Lorenzo Pieralisi wrote:

> On Mon, Sep 23, 2013 at 08:24:34PM +0100, Nicolas Pitre wrote:
> > 
> > Currently mcpm_cpu_power_down() and mcpm_cpu_suspend() trigger BUG()
> > if mcpm_platform_register() is not called beforehand.  This may occur
> > for many reasons such as some incomplete device tree passed to the kernel
> > or the like.
> > 
> > Let's be nicer to users and avoid killing the kernel if that happens by
> > logging a warning and returning to the caller.  The mcpm_cpu_suspend()
> > user is already set to deal with this situation, and so is cpu_die()
> > invoking mcpm_cpu_die().
> > 
> > The problematic case would have been the B.L switcher's usage of
> > mcpm_cpu_power_down(), however it has to call mcpm_cpu_power_up() first
> > which is already set to catch an error resulting from a missing
> > mcpm_platform_register() call.
> > 
> > Signed-off-by: Nicolas Pitre <nico at linaro.org>
> > 
> > diff --git a/arch/arm/common/mcpm_entry.c b/arch/arm/common/mcpm_entry.c
> > index 370236dd1a..3fd43f1fd2 100644
> > --- a/arch/arm/common/mcpm_entry.c
> > +++ b/arch/arm/common/mcpm_entry.c
> > @@ -51,7 +51,8 @@ void mcpm_cpu_power_down(void)
> >  {
> >  	phys_reset_t phys_reset;
> >  
> > -	BUG_ON(!platform_ops);
> > +	if (WARN_ON_ONCE(!platform_ops))
> > +		return;
> >  	BUG_ON(!irqs_disabled());
> 
> I think it should be:
> 
> if (WARN_ON_ONCE(!platform_ops || !platform_ops->power_down))
> 	return;
> 
> since even if platform_ops has been initialized we might still be end
> up with a NULL function pointer.

Good point.

> Probably the test for the function pointer belongs in:
> 
> mcpm_platform_register()

Well, some methods may be optional.  For example there is no suspend 
support possible with the DCSCB backend.  And you can't do much in 
mcpm_platform_register() other than refuse the whole registration even 
though some methods are still usable.

Amended patch below.

From: Nicolas Pitre <nicolas.pitre at linaro.org>
Date: Mon, 23 Sep 2013 14:08:05 -0400
Subject: [PATCH] ARM: MCPM: don't explode if invoked without being initialized first

Currently mcpm_cpu_power_down() and mcpm_cpu_suspend() trigger BUG()
if mcpm_platform_register() is not called beforehand.  This may occur
for many reasons such as some incomplete device tree passed to the kernel
or the like.

Let's be nicer to users and avoid killing the kernel if that happens by
logging a warning and returning to the caller.  The mcpm_cpu_suspend()
user is already set to deal with this situation, and so is cpu_die()
invoking mcpm_cpu_die().

The problematic case would have been the B.L switcher's usage of
mcpm_cpu_power_down(), however it has to call mcpm_cpu_power_up() first
which is already set to catch an error resulting from a missing
mcpm_platform_register() call.

Signed-off-by: Nicolas Pitre <nico at linaro.org>

diff --git a/arch/arm/common/mcpm_entry.c b/arch/arm/common/mcpm_entry.c
index 370236dd1a..990250965f 100644
--- a/arch/arm/common/mcpm_entry.c
+++ b/arch/arm/common/mcpm_entry.c
@@ -51,7 +51,8 @@ void mcpm_cpu_power_down(void)
 {
 	phys_reset_t phys_reset;
 
-	BUG_ON(!platform_ops);
+	if (WARN_ON_ONCE(!platform_ops || !platform_ops->power_down))
+		return;
 	BUG_ON(!irqs_disabled());
 
 	/*
@@ -93,7 +94,8 @@ void mcpm_cpu_suspend(u64 expected_residency)
 {
 	phys_reset_t phys_reset;
 
-	BUG_ON(!platform_ops);
+	if (WARN_ON_ONCE(!platform_ops || !platform_ops->suspend))
+		return;
 	BUG_ON(!irqs_disabled());
 
 	/* Very similar to mcpm_cpu_power_down() */
diff --git a/arch/arm/include/asm/mcpm.h b/arch/arm/include/asm/mcpm.h
index 0f7b7620e9..fc82a88f5b 100644
--- a/arch/arm/include/asm/mcpm.h
+++ b/arch/arm/include/asm/mcpm.h
@@ -76,8 +76,11 @@ int mcpm_cpu_power_up(unsigned int cpu, unsigned int cluster);
  *
  * This must be called with interrupts disabled.
  *
- * This does not return.  Re-entry in the kernel is expected via
- * mcpm_entry_point.
+ * On success this does not return.  Re-entry in the kernel is expected
+ * via mcpm_entry_point.
+ *
+ * This will return if mcpm_platform_register() has not been called
+ * previously in which case the caller should take appropriate action.
  */
 void mcpm_cpu_power_down(void);
 
@@ -98,8 +101,11 @@ void mcpm_cpu_power_down(void);
  *
  * This must be called with interrupts disabled.
  *
- * This does not return.  Re-entry in the kernel is expected via
- * mcpm_entry_point.
+ * On success this does not return.  Re-entry in the kernel is expected
+ * via mcpm_entry_point.
+ *
+ * This will return if mcpm_platform_register() has not been called
+ * previously in which case the caller should take appropriate action.
  */
 void mcpm_cpu_suspend(u64 expected_residency);