[linux-pm] [RFC/PATCH v2] PM / Runtime: allow _put_sync() from interrupts-disabled context

[Rafael J. Wysocki]

On Friday, July 22, 2011, Kevin Hilman wrote:
> Currently the use of pm_runtime_put_sync() is not safe from
> interrupts-disabled context because rpm_idle() will release the
> spinlock and enable interrupts for the idle callbacks.  This enables
> interrupts during a time where interrupts were expected to be
> disabled, and can have strange side effects on drivers that expected
> interrupts to be disabled.
> 
> This is not a bug since the documentation clearly states that only
> _put_sync_suspend() is safe in IRQ-safe mode.
> 
> However, pm_runtime_put_sync() could be made safe when in IRQ-safe
> mode by releasing the spinlock but not re-enabling interrupts, which
> is what this patch aims to do.
> 
> Problem was found when using some buggy drivers that set
> pm_runtime_irq_safe() and used _put_sync() in interrupts-disabled
> context.
> 
> The offending drivers have been fixed to use _put_sync_suspend(),
> But this patch is an RFC to see if it might make sense to allow
> using _put_sync() from interrupts-disabled context.

OK, I'm going to take this for 3.2.

Thanks,
Rafael


> Reported-by: Colin Cross <ccross at google.com>
> Tested-by: Nishanth Menon <nm at ti.com>
> Signed-off-by: Kevin Hilman <khilman at ti.com>
> ---
> v2: update documentation also
> 
>  Documentation/power/runtime_pm.txt |   10 +++++-----
>  drivers/base/power/runtime.c       |   10 ++++++++--
>  2 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
> index 14dd3c6..4ce5450 100644
> --- a/Documentation/power/runtime_pm.txt
> +++ b/Documentation/power/runtime_pm.txt
> @@ -54,11 +54,10 @@ referred to as subsystem-level callbacks in what follows.
>  By default, the callbacks are always invoked in process context with interrupts
>  enabled.  However, subsystems can use the pm_runtime_irq_safe() helper function
>  to tell the PM core that a device's ->runtime_suspend() and ->runtime_resume()
> -callbacks should be invoked in atomic context with interrupts disabled
> -(->runtime_idle() is still invoked the default way).  This implies that these
> -callback routines must not block or sleep, but it also means that the
> -synchronous helper functions listed at the end of Section 4 can be used within
> -an interrupt handler or in an atomic context.
> +callbacks should be invoked in atomic context with interrupts disabled.
> +This implies that these callback routines must not block or sleep, but it also
> +means that the synchronous helper functions listed at the end of Section 4 can
> +be used within an interrupt handler or in an atomic context.
>  
>  The subsystem-level suspend callback is _entirely_ _responsible_ for handling
>  the suspend of the device as appropriate, which may, but need not include
> @@ -483,6 +482,7 @@ pm_runtime_suspend()
>  pm_runtime_autosuspend()
>  pm_runtime_resume()
>  pm_runtime_get_sync()
> +pm_runtime_put_sync()
>  pm_runtime_put_sync_suspend()
>  
>  5. Runtime PM Initialization, Device Probing and Removal
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 8dc247c..acb3f83 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -226,11 +226,17 @@ static int rpm_idle(struct device *dev, int rpmflags)
>  		callback = NULL;
>  
>  	if (callback) {
> -		spin_unlock_irq(&dev->power.lock);
> +		if (dev->power.irq_safe)
> +			spin_unlock(&dev->power.lock);
> +		else
> +			spin_unlock_irq(&dev->power.lock);
>  
>  		callback(dev);
>  
> -		spin_lock_irq(&dev->power.lock);
> +		if (dev->power.irq_safe)
> +			spin_lock(&dev->power.lock);
> +		else
> +			spin_lock_irq(&dev->power.lock);
>  	}
>  
>  	dev->power.idle_notification = false;
>