linux-kernel - Re: [PATCH v2 02/12] reboot: reboot, not shutdown, on hw_protection

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Message-ID: <de781a07-d209-4bbe-8945-efcb4490f604@pengutronix.de>
Date: Mon, 17 Feb 2025 21:22:06 +0100
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Matti Vaittinen <mazziesaccount@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Fabio Estevam
 <festevam@...x.de>, "Rafael J. Wysocki" <rafael@...nel.org>,
 Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>,
 Jonathan Corbet <corbet@....net>, Serge Hallyn <serge@...lyn.com>,
 Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 Benson Leung <bleung@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>,
 Guenter Roeck <groeck@...omium.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-security-module@...r.kernel.org,
 chrome-platform@...ts.linux.dev, devicetree@...r.kernel.org,
 kernel@...gutronix.de
Subject: Re: [PATCH v2 02/12] reboot: reboot, not shutdown, on
 hw_protection_reboot timeout

Hello Matti,

On 22.01.25 12:28, Matti Vaittinen wrote:
> On 13/01/2025 18:25, Ahmad Fatoum wrote:
>> hw_protection_shutdown() will kick off an orderly shutdown and if that
>> takes longer than a configurable amount of time, an emergency shutdown
>> will occur.
>>
>> Recently, hw_protection_reboot() was added for those systems that don't
>> implement a proper shutdown and are better served by rebooting and
>> having the boot firmware worry about doing something about the critical
>> condition.
>>
>> On timeout of the orderly reboot of hw_protection_reboot(), the system
>> would go into shutdown, instead of reboot. This is not a good idea, as
>> going into shutdown was explicitly not asked for.
>>
>> Fix this by always doing an emergency reboot if hw_protection_reboot()
>> is called and the orderly reboot takes too long.
>>
>> Fixes: 79fa723ba84c ("reboot: Introduce thermal_zone_device_critical_reboot()")
>> Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
>> ---
>>   kernel/reboot.c | 70 ++++++++++++++++++++++++++++++++++++++++-----------------
>>   1 file changed, 49 insertions(+), 21 deletions(-)
>>
>> diff --git a/kernel/reboot.c b/kernel/reboot.c
>> index 847ac5d17a659981c6765699eac323f5e87f48c1..222b63dfd31020d0e2bc1b1402dbfa82adc71990 100644
>> --- a/kernel/reboot.c
>> +++ b/kernel/reboot.c
>> @@ -932,48 +932,76 @@ void orderly_reboot(void)
>>   }
>>   EXPORT_SYMBOL_GPL(orderly_reboot);
>>   +static const char *hw_protection_action_str(enum hw_protection_action action)
>> +{
>> +    switch (action) {
>> +    case HWPROT_ACT_SHUTDOWN:
>> +        return "shutdown";
>> +    case HWPROT_ACT_REBOOT:
>> +        return "reboot";
>> +    default:
>> +        return "undefined";
>> +    }
>> +}
>> +
>> +static enum hw_protection_action hw_failure_emergency_action;
> 
> nit: Do we have a (theoretical) possibility that two emergency restarts get scheduled with different actions? Should the action be allocated (maybe not) for each caller, or should there be a check if an operation with conflicting action is already scheduled?
> 
> If this was already considered and thought it is not an issue:
> 
> Reviewed-by: Matti Vaittinen <mazziesaccount@...il.com>

__hw_protection_trigger (née __hw_protection_shutdown) has this at its start:

 static atomic_t allow_proceed = ATOMIC_INIT(1);

 /* Shutdown should be initiated only once. */
 if (!atomic_dec_and_test(&allow_proceed))
         return;

It's thus not possible to have a later emergency restart race against the first.

Thanks for your R-b,
Ahmad

> 
> 
> Yours,
>     -- Matti
> 


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