Re: [PATCH 2/4] arm64: hibernate: remove WARN_ON in save_processor_state

[Song Shuai]

在 2023/6/5 22:28, Will Deacon 写道:
> On Thu, May 25, 2023 at 10:55:53AM +0800, Song Shuai wrote:
> > During hibernation or restoration, freeze_secondary_cpus
> > checks num_online_cpus via BUG_ON, and the subsequent
> > save_processor_state also does the checking with WARN_ON.
> >
> > So remove the unnecessary checking in save_processor_state.
>
> This is a very terse summary of why this is safe.
>
> Looking at the code, freeze_secondary_cpus() does indeed check
> num_online_cpus(), or it returns an error which then causes the hibernation
> to fail. However, this is all in the CONFIG_PM_SLEEP_SMP=y case and it's
> far less clear whether your assertion is true if that option is disabled.
>
> Please can you describe your reasoning in more detail, and cover the case
> where CONFIG_PM_SLEEP_SMP=n as well, please?

With HIBERNATION enabled, the sole possible condition to disable 
CONFIG_PM_SLEEP_SMP
is !SMP where num_online_cpus is always 1. We also don't have to check 
it in save_processor_state.

> Will

--
Thanks
Song Shuai