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SubjectRe: pm_runtime_resume_and_get in .remove callbacks
On Wed, Jul 13, 2022 at 10:47 AM Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> wrote:
>
> Hello,
>
> there is a big bunch of kernel drivers (here:
> drivers/i2c/busses/i2c-sprd.c) that have a remove callback that looks as
> follows:
>
> static int sprd_i2c_remove(struct platform_device *pdev)
> {
> struct sprd_i2c *i2c_dev = platform_get_drvdata(pdev);
> int ret;
>
> ret = pm_runtime_resume_and_get(i2c_dev->dev);
> if (ret < 0)
> return ret;
>
> i2c_del_adapter(&i2c_dev->adap);
> clk_disable_unprepare(i2c_dev->clk);
>
> pm_runtime_put_noidle(i2c_dev->dev);
> pm_runtime_disable(i2c_dev->dev);
>
> return 0;
> }
>
> If pm_runtime_resume_and_get fails, the i2c adapter isn't removed, but
> as the memory backing i2c_dev goes away---it was allocated using
> devm_kzalloc in .probe()---the next i2c action will probably access
> freed memory.
>
> I'm not familiar enough with pm-runtime stuff, but wonder what
> can/should be done about that. The obvious (to me) candidates are:
>
> - log an error if pm_runtime_resume_and_get() fails, but continue to
> clean up
> - don't check the return value at all
>
> What do you think?

(1) Use pm_runtime_get_sync() instead of pm_runtime_resume_and_get()
and don't check its return value,

or if that is not viable, because something really can run if and only
if the device is operational,

(2) do something like

ret = pm_runtime_resume_and_get(i2c_dev->dev);
i2c_del_adapter(&i2c_dev->adap);
if (ret >= 0)
clk_disable_unprepare(i2c_dev->clk);

pm_runtime_put_noidle(i2c_dev->dev);
pm_runtime_disable(i2c_dev->dev);

Thanks!

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