2023-04-02 10:53:33

by Uwe Kleine-König

Subject: [PATCH RFC] PM: runtime: Drop device usage only after remove is done

Many device drivers call one of the variants of pm_runtime_resume() in
their remove callback. So calling pm_runtime_put_sync() just before that
is ineffective as the suspend callback might just be called just to
resume the device directly afterwards again.

Signed-off-by: Uwe Kleine-König <[email protected]>
---
Hello,

this is a theoretical issue that I noticed while doing some research how
pm-runtime works. Not sure it makes sense, so I marked it as RFC.

Best regards
Uwe

drivers/base/dd.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 8def2ba08a82..6beac141d3d2 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -1235,10 +1235,10 @@ static void __device_release_driver(struct device *dev, struct device *parent)

bus_notify(dev, BUS_NOTIFY_UNBIND_DRIVER);

- pm_runtime_put_sync(dev);
-
device_remove(dev);

+ pm_runtime_put_sync(dev);
+
if (dev->bus && dev->bus->dma_cleanup)
dev->bus->dma_cleanup(dev);


base-commit: fe15c26ee26efa11741a7b632e9f23b01aca4cc6
--
2.39.2

2023-04-03 19:22:47

by Wysocki, Rafael J

Subject: Re: [PATCH RFC] PM: runtime: Drop device usage only after remove is done

CC-ing linux-pm would have been nice (done now).

On 4/2/2023 12:39 PM, Uwe Kleine-König wrote:
> Many device drivers call one of the variants of pm_runtime_resume() in
> their remove callback. So calling pm_runtime_put_sync() just before that
> is ineffective as the suspend callback might just be called just to
> resume the device directly afterwards again.
>
> Signed-off-by: Uwe Kleine-König <[email protected]>
> ---
> Hello,
>
> this is a theoretical issue that I noticed while doing some research how
> pm-runtime works. Not sure it makes sense, so I marked it as RFC.
>
> Best regards
> Uwe
>
> drivers/base/dd.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 8def2ba08a82..6beac141d3d2 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -1235,10 +1235,10 @@ static void __device_release_driver(struct device *dev, struct device *parent)
>
> bus_notify(dev, BUS_NOTIFY_UNBIND_DRIVER);
>
> - pm_runtime_put_sync(dev);
> -
> device_remove(dev);
>
> + pm_runtime_put_sync(dev);
> +
> if (dev->bus && dev->bus->dma_cleanup)
> dev->bus->dma_cleanup(dev);
>
>
> base-commit: fe15c26ee26efa11741a7b632e9f23b01aca4cc6