linux-kernel - Re: [PATCH] kernel/reboot: emergency_restart: set correct system

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Date:   Tue, 21 Mar 2023 05:12:19 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Benjamin Bara <bbara93@...il.com>, rafael.j.wysocki@...el.com,
        pmladek@...e.com
Cc:     mcgrof@...nel.org, paulmck@...nel.org, kai.heng.feng@...onical.com,
        tangmeng@...ontech.com, john.ogness@...utronix.de,
        yuehaibing@...wei.com, benjamin.bara@...data.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/reboot: emergency_restart: set correct
 system_state

On 3/21/23 00:32, Benjamin Bara wrote:
> From: Benjamin Bara <benjamin.bara@...data.com>
> 
> As the emergency restart does not call kernel_restart_prepare(),
> the system_state stays in SYSTEM_RUNNING.
> 
> This e.g. hinders i2c_in_atomic_xfer_mode() from becoming active,
> and therefore might lead to avoidable warnings in the restart handlers,
> e.g.:
> [   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
> [   12.676926] Voluntary context switch within RCU read-side critical section!
> ...
> [   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
> [   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
> ...
> [   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
> [   13.001050]  machine_restart from panic+0x2a8/0x32c
> 
> Avoid these by setting the correct system_state.
> 
> Signed-off-by: Benjamin Bara <benjamin.bara@...data.com>
> ---
>  kernel/reboot.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index 3bba88c7ffc6..6ebef11c8876 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -74,6 +74,7 @@ void __weak (*pm_power_off)(void);
>  void emergency_restart(void)
>  {
>  	kmsg_dump(KMSG_DUMP_EMERG);
> +	system_state = SYSTEM_RESTART;
>  	machine_emergency_restart();
>  }
>  EXPORT_SYMBOL_GPL(emergency_restart);

This patch needs to be paired with the i2c_in_atomic_xfer_mode() change.
Please also add the v5.2+ stable tag to the commit messages.

-- 
Best regards,
Dmitry