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

[Peter Wang <peter.wang@mediatek.com>]

On 7/1/22 3:16 AM, 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(-)
>
> Index: linux-pm/drivers/base/power/runtime.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/runtime.c
> +++ linux-pm/drivers/base/power/runtime.c
> @@ -1768,7 +1768,6 @@ void pm_runtime_get_suppliers(struct dev
>   		if (link->flags & DL_FLAG_PM_RUNTIME) {
>   			link->supplier_preactivated = true;
>   			pm_runtime_get_sync(link->supplier);
> -			refcount_inc(&link->rpm_active);
>   		}
>   
>   	device_links_read_unlock(idx);
> @@ -1788,19 +1787,8 @@ void pm_runtime_put_suppliers(struct dev
>   	list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
>   				device_links_read_lock_held())
>   		if (link->supplier_preactivated) {
> -			bool put;
> -
>   			link->supplier_preactivated = false;
> -
> -			spin_lock_irq(&dev->power.lock);
> -
> -			put = pm_runtime_status_suspended(dev) &&
> -			      refcount_dec_not_one(&link->rpm_active);
> -
> -			spin_unlock_irq(&dev->power.lock);
> -
> -			if (put)
> -				pm_runtime_put(link->supplier);
> +			pm_runtime_put(link->supplier);
>   		}
>   
>   	device_links_read_unlock(idx);
> Index: linux-pm/drivers/base/core.c
> ===================================================================
> --- linux-pm.orig/drivers/base/core.c
> +++ linux-pm/drivers/base/core.c
> @@ -487,6 +487,16 @@ static void device_link_release_fn(struc
>   	device_link_synchronize_removal();
>   
>   	pm_runtime_release_supplier(link);
> +	/*
> +	 * If supplier_preactivated is set, the link has been dropped between
> +	 * the pm_runtime_get_suppliers() and pm_runtime_put_suppliers() calls
> +	 * in __driver_probe_device().  In that case, drop the supplier's
> +	 * PM-runtime usage counter to remove the reference taken by
> +	 * pm_runtime_get_suppliers().
> +	 */
> +	if (link->supplier_preactivated)
> +		pm_runtime_put_noidle(link->supplier);
> +
>   	pm_request_idle(link->supplier);
>   
>   	put_device(link->consumer);

Thanks for fix this bug.
Reviewed-by: Peter Wang <peter.wang@mediatek.com>


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