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Date:   Wed, 7 Jun 2023 11:00:08 +0800
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Subject: Re: [PATCH 2/4] arm64: hibernate: remove WARN_ON in
 save_processor_state
To:     Will Deacon <will@kernel.org>
Cc:     catalin.marinas@arm.com, paul.walmsley@sifive.com,
        palmer@dabbelt.com, aou@eecs.berkeley.edu, chris@zankel.net,
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        jeeheng.sia@starfivetech.com, leyfoon.tan@starfivetech.com,
        linux@armlinux.org.uk, linux-arm-kernel@lists.infradead.org,
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References: <20230525025555.24104-1-songshuaishuai@tinylab.org>
 <20230525025555.24104-3-songshuaishuai@tinylab.org>
 <20230605142857.GE21212@willie-the-truck>
From:   Song Shuai <songshuaishuai@tinylab.org>
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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