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

[Kevin Hilman]

"Rafael J. Wysocki" <rjw at sisk.pl> writes:

> 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.

Rafael, 

Since you're planning to merge this, maybe we should consider merging
this as a fix for v3.1, and possibly even for v3.0 stable.  That way,
any current drivers using irq_safe and the normal _put_sync() will not
have this problem.

Kevin