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Date:   Thu, 8 Jun 2023 18:26:58 +0100
From:   Will Deacon <will@kernel.org>
To:     Song Shuai <songshuaishuai@tinylab.org>
Cc:     catalin.marinas@arm.com, paul.walmsley@sifive.com,
        palmer@dabbelt.com, aou@eecs.berkeley.edu, chris@zankel.net,
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        ajones@ventanamicro.com, conor.dooley@microchip.com,
        jeeheng.sia@starfivetech.com, leyfoon.tan@starfivetech.com,
        linux@armlinux.org.uk, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org
Subject: Re: [PATCH 2/4] arm64: hibernate: remove WARN_ON in
 save_processor_state
Message-ID: <20230608172656.GB1606@willie-the-truck>
References: <20230525025555.24104-1-songshuaishuai@tinylab.org>
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On Wed, Jun 07, 2023 at 11:00:08AM +0800, Song Shuai wrote:
> 
> 
> 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.

Thanks. Please add that to the commit message.

Will