Re: [PATCH v1] PM: sleep: core: Restrict power.set_active propagation

[Jon Hunter <jonathanh@nvidia.com>]

On 08/02/2025 17:54, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Commit 3775fc538f53 ("PM: sleep: core: Synchronize runtime PM status of
> parents and children") exposed an issue related to simple_pm_bus_pm_ops
> that uses pm_runtime_force_suspend() and pm_runtime_force_resume() as
> bus type PM callbacks for the noirq phases of system-wide suspend and
> resume.
> 
> The problem is that pm_runtime_force_suspend() does not distinguish
> runtime-suspended devices from devices for which runtime PM has never
> been enabled, so if it sees a device with runtime PM status set to
> RPM_ACTIVE, it will assume that runtime PM is enabled for that device
> and so it will attempt to suspend it with the help of its runtime PM
> callbacks which may not be ready for that.  As it turns out, this
> causes simple_pm_bus_runtime_suspend() to crash due to a NULL pointer
> dereference.
> 
> Another problem related to the above commit and simple_pm_bus_pm_ops is
> that setting runtime PM status of a device handled by the latter to
> RPM_ACTIVE will actually prevent it from being resumed because
> pm_runtime_force_resume() only resumes devices with runtime PM status
> set to RPM_SUSPENDED.
> 
> To mitigate these issues, do not allow power.set_active to propagate
> beyond the parent of the device with DPM_FLAG_SMART_SUSPEND set that
> will need to be resumed, which should be a sufficient stop-gap for the
> time being, but they will need to be properly addressed in the future
> because in general during system-wide resume it is necessary to resume
> all devices in a dependency chain in which at least one device is going
> to be resumed.
> 
> Fixes: 3775fc538f53 ("PM: sleep: core: Synchronize runtime PM status of parents and children")
> Closes: https://lore.kernel.org/linux-pm/1c2433d4-7e0f-4395-b841-b8eac7c25651@nvidia.com/
> Reported-by: Jon Hunter <jonathanh@nvidia.com>
> Tested-by: Johan Hovold <johan+linaro@kernel.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>   drivers/base/power/main.c |   21 +++++++++------------
>   1 file changed, 9 insertions(+), 12 deletions(-)
> 
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -1191,24 +1191,18 @@
>   	return PMSG_ON;
>   }
>   
> -static void dpm_superior_set_must_resume(struct device *dev, bool set_active)
> +static void dpm_superior_set_must_resume(struct device *dev)
>   {
>   	struct device_link *link;
>   	int idx;
>   
> -	if (dev->parent) {
> +	if (dev->parent)
>   		dev->parent->power.must_resume = true;
> -		if (set_active)
> -			dev->parent->power.set_active = true;
> -	}
>   
>   	idx = device_links_read_lock();
>   
> -	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node) {
> +	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
>   		link->supplier->power.must_resume = true;
> -		if (set_active)
> -			link->supplier->power.set_active = true;
> -	}
>   
>   	device_links_read_unlock(idx);
>   }
> @@ -1287,9 +1281,12 @@
>   		dev->power.must_resume = true;
>   
>   	if (dev->power.must_resume) {
> -		dev->power.set_active = dev->power.set_active ||
> -			dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND);
> -		dpm_superior_set_must_resume(dev, dev->power.set_active);
> +		if (dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND)) {
> +			dev->power.set_active = true;
> +			if (dev->parent && !dev->parent->power.ignore_children)
> +				dev->parent->power.set_active = true;
> +		}
> +		dpm_superior_set_must_resume(dev);
>   	}
>   
>   Complete:
> 

Thanks for fixing!

Tested-by: Jon Hunter <jonathanh@nvidia.com>

Jon

-- 
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