Re: [PATCH v3] PM: sleep: core: Avoid setting power.must_resume to false
From: Greg KH
Date: Fri Aug 13 2021 - 03:23:45 EST
On Tue, Aug 10, 2021 at 01:05:38PM -0700, Prasad Sodagudi wrote:
> There are variables(power.may_skip_resume and dev->power.must_resume)
> and DPM_FLAG_MAY_SKIP_RESUME flags to control the resume of devices after
> a system wide suspend transition.
>
> Setting the DPM_FLAG_MAY_SKIP_RESUME flag means that the driver allows
> its "noirq" and "early" resume callbacks to be skipped if the device
> can be left in suspend after a system-wide transition into the working
> state. PM core determines that the driver's "noirq" and "early" resume
> callbacks should be skipped or not with dev_pm_skip_resume() function by
> checking power.may_skip_resume variable.
>
> power.must_resume variable is getting set to false in __device_suspend()
> function without checking device's DPM_FLAG_MAY_SKIP_RESUME and
> dev->power.usage_count variables. In problematic scenario, where
> all the devices in the suspend_late stage are successful and some
> device can fail to suspend in suspend_noirq phase. So some devices
> successfully suspended in suspend_late stage are not getting chance
> to execute __device_suspend_noirq() to set dev->power.must_resume
> variable to true and not getting resumed in early_resume phase.
>
> Add a check for device's DPM_FLAG_MAY_SKIP_RESUME flag before
> setting power.must_resume variable in __device_suspend function.
>
> Fixes: 6e176bf8d461 ("PM: sleep: core: Do not skip callbacks in the resume phase")
> Signed-off-by: Prasad Sodagudi <psodagud@xxxxxxxxxxxxxx>
> ---
> V2 -> V3: Format issues patch posting
> V1 -> V2: Fixed indentation and commit text to include scenario
> drivers/base/power/main.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index d568772..9ee6987 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -1642,7 +1642,11 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
> }
>
> dev->power.may_skip_resume = true;
> - dev->power.must_resume = false;
> + if ((atomic_read(&dev->power.usage_count) <= 1) &&
> + (dev_pm_test_driver_flags(dev, DPM_FLAG_MAY_SKIP_RESUME)))
> + dev->power.must_resume = false;
> + else
> + dev->power.must_resume = true;
Again, what happens if the usage_count changes right after reading the
value? What protects that from happening?
thanks,
greg k-h