Re: [PATCH] PM: runtime: Fix supplier device management during consumer probe

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

On Thu, Jun 30, 2022 at 09:16:41PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Because pm_runtime_get_suppliers() bumps up the rpm_active counter
> of each device link to a supplier of the given device in addition
> to bumping up the supplier's PM-runtime usage counter, a runtime
> suspend of the consumer device may case the latter to go down to 0
> when pm_runtime_put_suppliers() is running on a remote CPU.  If that
> happens after pm_runtime_put_suppliers() has released power.lock for
> the consumer device, and a runtime resume of that device takes place
> immediately after it, before pm_runtime_put() is called for the
> supplier, that pm_runtime_put() call may cause the supplier to be
> suspended even though the consumer is active.
> 
> To prevent that from happening, modify pm_runtime_get_suppliers() to
> call pm_runtime_get_sync() for the given device's suppliers without
> touching the rpm_active counters of the involved device links
> Accordingly, modify pm_runtime_put_suppliers() to call pm_runtime_put()
> for the given device's suppliers without looking at the rpm_active
> counters of the device links at hand.  [This is analogous to what
> happened before commit 4c06c4e6cf63 ("driver core: Fix possible
> supplier PM-usage counter imbalance").]
> 
> Since pm_runtime_get_suppliers() sets supplier_preactivated for each
> device link where the supplier's PM-runtime usage counter has been
> incremented and pm_runtime_put_suppliers() calls pm_runtime_put() for
> the suppliers whose device links have supplier_preactivated set, the
> PM-runtime usage counter is balanced for each supplier and this is
> independent of the runtime suspend and resume of the consumer device.
> 
> However, in case a device link with DL_FLAG_PM_RUNTIME set is dropped
> during the consumer device probe, so pm_runtime_get_suppliers() bumps
> up the supplier's PM-runtime usage counter, but it cannot be dropped by
> pm_runtime_put_suppliers(), make device_link_release_fn() take care of
> that.
> 
> Fixes: 4c06c4e6cf63 ("driver core: Fix possible supplier PM-usage counter imbalance")
> Reported-by: Peter Wang <peter.wang@mediatek.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/base/core.c          |   10 ++++++++++
>  drivers/base/power/runtime.c |   14 +-------------
>  2 files changed, 11 insertions(+), 13 deletions(-)

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