Re: [PATCH v3 1/3] leds: triggers: Allow to switch the trigger to "panic" on a kernel panic

[Jacek Anaszewski]

On 04/29/2016 09:20 AM, Jacek Anaszewski wrote:
> Hi Ezequiel,
>
> Thanks for the update. It's indeed reasonable to have all the
> switching infrastructure in ledtrig-panic.c.
>
> I've noticed two minor issues below.

Since the merge window is imminent, I've addressed those issues by
myself and applied the patch set to the for-next branch
of linux-leds.git.

Thanks,
Jacek Anaszewski

> On 04/29/2016 12:03 AM, Ezequiel Garcia wrote:
> > This commit adds a new led_cdev flag LED_PANIC_INDICATOR, which
> > allows to mark a specific LED to be switched to the "panic"
> > trigger, on a kernel panic.
> >
> > This is useful to allow the user to assign a regular trigger
> > to a given LED, and still blink that LED on a kernel panic.
> >
> > Signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/leds/led-triggers.c          |  2 +-
> >   drivers/leds/leds.h                  |  1 +
> >   drivers/leds/trigger/Kconfig         |  3 +++
> >   drivers/leds/trigger/ledtrig-panic.c | 47
> > ++++++++++++++++++++++++++++++++++++
> >   include/linux/leds.h                 |  1 +
> >   5 files changed, 53 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
> > index 2181581795d3..55fa65e1ae03 100644
> > --- a/drivers/leds/led-triggers.c
> > +++ b/drivers/leds/led-triggers.c
> > @@ -26,7 +26,7 @@
> >    * Nests outside led_cdev->trigger_lock
> >    */
> >   static DECLARE_RWSEM(triggers_list_lock);
> > -static LIST_HEAD(trigger_list);
> > +LIST_HEAD(trigger_list);
> >
> >    /* Used by LED Class */
> >
> > diff --git a/drivers/leds/leds.h b/drivers/leds/leds.h
> > index db3f20da7221..7d38e6b9a740 100644
> > --- a/drivers/leds/leds.h
> > +++ b/drivers/leds/leds.h
> > @@ -30,5 +30,6 @@ void led_set_brightness_nosleep(struct led_classdev
> > *led_cdev,
> >
> >   extern struct rw_semaphore leds_list_lock;
> >   extern struct list_head leds_list;
> > +extern struct list_head trigger_list;
> >
> >   #endif    /* __LEDS_H_INCLUDED */
> > diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
> > index beac8c31c51b..4e4521c9072a 100644
> > --- a/drivers/leds/trigger/Kconfig
> > +++ b/drivers/leds/trigger/Kconfig
> > @@ -121,6 +121,9 @@ config LEDS_TRIGGER_PANIC
> >       depends on LEDS_TRIGGERS
> >       help
> >         This allows LEDs to be configured to blink on a kernel panic.
> > +      Enabling this option will allow to mark certain LEDs as
> > 'panic-indicators',
>
> s/"panic-indicators"/panic indicators/
>
> I understand that you referred here to the DT property name, but this
> is not obvious at first glance, and it is an implementation detail.
>
> > +      allowing to blink them on a kernel panic, even if they are set to
> > +      a different trigger.
> >         If unsure, say Y.
> >
> >   endif # LEDS_TRIGGERS
> > diff --git a/drivers/leds/trigger/ b/drivers/leds/trigger/ledtrig-panic.c
> > index 627b350c5ec3..3e447bd2064a 100644
> > --- a/drivers/leds/trigger/ledtrig-panic.c
> > +++ b/drivers/leds/trigger/ledtrig-panic.c
> > @@ -11,10 +11,54 @@
> >
> >   #include <linux/kernel.h>
> >   #include <linux/init.h>
> > +#include <linux/notifier.h>
> >   #include <linux/leds.h>
> > +#include "../leds.h"
> >
> >   static struct led_trigger *trigger;
> >
> > +/*
> > + * This is a called in a special context by the atomic panic
>
> s/is a/is/
>
> > + * notifier. This means the trigger can be changed without
> > + * worrying about locking.
> > + */
> > +static void led_trigger_set_panic(struct led_classdev *led_cdev)
> > +{
> > +    struct led_trigger *trig;
> > +
> > +    list_for_each_entry(trig, &trigger_list, next_trig) {
> > +        if (strcmp("panic", trig->name))
> > +            continue;
> > +        if (led_cdev->trigger)
> > +            list_del(&led_cdev->trig_list);
> > +        list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
> > +
> > +        /* Avoid the delayed blink path */
> > +        led_cdev->blink_delay_on = 0;
> > +        led_cdev->blink_delay_off = 0;
> > +
> > +        led_cdev->trigger = trig;
> > +        if (trig->activate)
> > +            trig->activate(led_cdev);
> > +        break;
> > +    }
> > +}
> > +
> > +static int led_trigger_panic_notifier(struct notifier_block *nb,
> > +                      unsigned long code, void *unused)
> > +{
> > +    struct led_classdev *led_cdev;
> > +
> > +    list_for_each_entry(led_cdev, &leds_list, node)
> > +        if (led_cdev->flags & LED_PANIC_INDICATOR)
> > +            led_trigger_set_panic(led_cdev);
> > +    return NOTIFY_DONE;
> > +}
> > +
> > +static struct notifier_block led_trigger_panic_nb = {
> > +    .notifier_call = led_trigger_panic_notifier,
> > +};
> > +
> >   static long led_panic_blink(int state)
> >   {
> >       led_trigger_event(trigger, state ? LED_FULL : LED_OFF);
> > @@ -23,6 +67,9 @@ static long led_panic_blink(int state)
> >
> >   static int __init ledtrig_panic_init(void)
> >   {
> > +    atomic_notifier_chain_register(&panic_notifier_list,
> > +                       &led_trigger_panic_nb);
> > +
> >       led_trigger_register_simple("panic", &trigger);
> >       panic_blink = led_panic_blink;
> >       return 0;
> > diff --git a/include/linux/leds.h b/include/linux/leds.h
> > index 19eb10278bea..7e9fb00e15e8 100644
> > --- a/include/linux/leds.h
> > +++ b/include/linux/leds.h
> > @@ -50,6 +50,7 @@ struct led_classdev {
> >   #define LED_SYSFS_DISABLE    (1 << 22)
> >   #define LED_DEV_CAP_FLASH    (1 << 23)
> >   #define LED_HW_PLUGGABLE    (1 << 24)
> > +#define LED_PANIC_INDICATOR    (1 << 25)
> >
> >       /* Set LED brightness level
> >        * Must not sleep. Use brightness_set_blocking for drivers