Date:   Fri, 29 Apr 2022 11:34:51 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Helge Deller <deller@....de>, akpm@...ux-foundation.org,
        bhe@...hat.com, pmladek@...e.com, kexec@...ts.infradead.org
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        linux-edac@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-leds@...r.kernel.org, linux-mips@...r.kernel.org,
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        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>
Subject: Re: [PATCH 12/30] parisc: Replace regular spinlock with spin_trylock
 on panic path

On 28/04/2022 13:55, Helge Deller wrote:
> [...]
> You may add:
> Acked-by: Helge Deller <deller@....de> # parisc
> 
> Helge

Thanks Helge, added!
Cheers,


Guilherme

> 
> 
>> ---
>>  arch/parisc/include/asm/pdc.h |  1 +
>>  arch/parisc/kernel/firmware.c | 27 +++++++++++++++++++++++----
>>  drivers/parisc/power.c        | 17 ++++++++++-------
>>  3 files changed, 34 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/parisc/include/asm/pdc.h b/arch/parisc/include/asm/pdc.h
>> index b643092d4b98..7a106008e258 100644
>> --- a/arch/parisc/include/asm/pdc.h
>> +++ b/arch/parisc/include/asm/pdc.h
>> @@ -83,6 +83,7 @@ int pdc_do_firm_test_reset(unsigned long ftc_bitmap);
>>  int pdc_do_reset(void);
>>  int pdc_soft_power_info(unsigned long *power_reg);
>>  int pdc_soft_power_button(int sw_control);
>> +int pdc_soft_power_button_panic(int sw_control);
>>  void pdc_io_reset(void);
>>  void pdc_io_reset_devices(void);
>>  int pdc_iodc_getc(void);
>> diff --git a/arch/parisc/kernel/firmware.c b/arch/parisc/kernel/firmware.c
>> index 6a7e315bcc2e..0e2f70b592f4 100644
>> --- a/arch/parisc/kernel/firmware.c
>> +++ b/arch/parisc/kernel/firmware.c
>> @@ -1232,15 +1232,18 @@ int __init pdc_soft_power_info(unsigned long *power_reg)
>>  }
>>
>>  /*
>> - * pdc_soft_power_button - Control the soft power button behaviour
>> - * @sw_control: 0 for hardware control, 1 for software control
>> + * pdc_soft_power_button{_panic} - Control the soft power button behaviour
>> + * @sw_control: 0 for hardware control, 1 for software control
>>   *
>>   *
>>   * This PDC function places the soft power button under software or
>>   * hardware control.
>> - * Under software control the OS may control to when to allow to shut
>> - * down the system. Under hardware control pressing the power button
>> + * Under software control the OS may control to when to allow to shut
>> + * down the system. Under hardware control pressing the power button
>>   * powers off the system immediately.
>> + *
>> + * The _panic version relies in spin_trylock to prevent deadlock
>> + * on panic path.
>>   */
>>  int pdc_soft_power_button(int sw_control)
>>  {
>> @@ -1254,6 +1257,22 @@ int pdc_soft_power_button(int sw_control)
>>  	return retval;
>>  }
>>
>> +int pdc_soft_power_button_panic(int sw_control)
>> +{
>> +	int retval;
>> +	unsigned long flags;
>> +
>> +	if (!spin_trylock_irqsave(&pdc_lock, flags)) {
>> +		pr_emerg("Couldn't enable soft power button\n");
>> +		return -EBUSY; /* ignored by the panic notifier */
>> +	}
>> +
>> +	retval = mem_pdc_call(PDC_SOFT_POWER, PDC_SOFT_POWER_ENABLE, __pa(pdc_result), sw_control);
>> +	spin_unlock_irqrestore(&pdc_lock, flags);
>> +
>> +	return retval;
>> +}
>> +
>>  /*
>>   * pdc_io_reset - Hack to avoid overlapping range registers of Bridges devices.
>>   * Primarily a problem on T600 (which parisc-linux doesn't support) but
>> diff --git a/drivers/parisc/power.c b/drivers/parisc/power.c
>> index 456776bd8ee6..8512884de2cf 100644
>> --- a/drivers/parisc/power.c
>> +++ b/drivers/parisc/power.c
>> @@ -37,7 +37,6 @@
>>  #include <linux/module.h>
>>  #include <linux/init.h>
>>  #include <linux/kernel.h>
>> -#include <linux/notifier.h>
>>  #include <linux/panic_notifier.h>
>>  #include <linux/reboot.h>
>>  #include <linux/sched/signal.h>
>> @@ -175,16 +174,21 @@ static void powerfail_interrupt(int code, void *x)
>>
>>
>>
>> -/* parisc_panic_event() is called by the panic handler.
>> - * As soon as a panic occurs, our tasklets above will not be
>> - * executed any longer. This function then re-enables the
>> - * soft-power switch and allows the user to switch off the system
>> +/*
>> + * parisc_panic_event() is called by the panic handler.
>> + *
>> + * As soon as a panic occurs, our tasklets above will not
>> + * be executed any longer. This function then re-enables
>> + * the soft-power switch and allows the user to switch off
>> + * the system. We rely in pdc_soft_power_button_panic()
>> + * since this version spin_trylocks (instead of regular
>> + * spinlock), preventing deadlocks on panic path.
>>   */
>>  static int parisc_panic_event(struct notifier_block *this,
>>  		unsigned long event, void *ptr)
>>  {
>>  	/* re-enable the soft-power switch */
>> -	pdc_soft_power_button(0);
>> +	pdc_soft_power_button_panic(0);
>>  	return NOTIFY_DONE;
>>  }
>>
>> @@ -193,7 +197,6 @@ static struct notifier_block parisc_panic_block = {
>>  	.priority	= INT_MAX,
>>  };
>>
>> -
>>  static int __init power_init(void)
>>  {
>>  	unsigned long ret;
> 

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