Re: [PATCH] PM: runtime: Add safety net to supplier device release

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Dec 10, 2021 at 05:10:13PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Because refcount_dec_not_one() returns true if the target refcount
> becomes saturated, it is generally unsafe to use its return value as
> a loop termination condition, but that is what happens when a device
> link's supplier device is released during runtime PM suspend
> operations and on device link removal.
> 
> To address this, introduce pm_runtime_release_supplier() to be used
> in the above cases which will check the supplier device's runtime
> PM usage counter in addition to the refcount_dec_not_one() return
> value, so the loop can be terminated in case the rpm_active refcount
> value becomes invalid, and update the code in question to use it as
> appropriate.
> 
> This change is not expected to have any visible functional impact.
> 
> Reported-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/base/core.c          |    3 +--
>  drivers/base/power/runtime.c |   41 ++++++++++++++++++++++++++++++-----------
>  include/linux/pm_runtime.h   |    3 +++
>  3 files changed, 34 insertions(+), 13 deletions(-)
> 

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>