linux-kernel - Re: [PATCH v6 1/5] kernel/reboot: emergency_restart: set correct system

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Date:   Wed, 14 Jun 2023 19:06:50 -0500
From:   Nishanth Menon <nm@...com>
To:     Benjamin Bara <bbara93@...il.com>
CC:     Wolfram Sang <wsa@...nel.org>, Lee Jones <lee@...nel.org>,
        <rafael.j.wysocki@...el.com>, <dmitry.osipenko@...labora.com>,
        <peterz@...radead.org>, <jonathanh@...dia.com>,
        <richard.leitner@...ux.dev>, <treding@...dia.com>,
        <linux-kernel@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>,
        Benjamin Bara <benjamin.bara@...data.com>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH v6 1/5] kernel/reboot: emergency_restart: set correct
 system_state

On 21:02-20230509, 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.
> 
> Since bae1d3a05a8b, this 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.
> 
> Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
> Cc: stable@...r.kernel.org # v5.2+
> 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);
> 
> -- 
> 2.34.1
> 

Tested-by: Nishanth Menon <nm@...com>

This in addition to a deeper bug in our driver seems to have helped
resolve a report we had been looking at. Tested on beagleplay platform

https://lore.kernel.org/all/ZGeHMjlnob2GFyHF@francesco-nb.int.toradex.com/

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D