Re: [RFC PATCHv2 2/2] PM: compile-time configuration of devicesuspend/resume watchdogs.

[Colin Cross]

On Fri, May 10, 2013 at 2:28 PM, Zoran Markovic
<zoran.markovic@xxxxxxxxxx> wrote:
> Power management debug option to configure device suspend/resume watchdogs.
> Available options are:
>   1. Enable/disable the feature.
>   2. Select triggered watchdog action between:
>         - system panic (default)
>         - dump stacktrace
>         - log event

I don't see much point to logging the event but not printing the stack
trace, you can just disable the feature if you don't want your logs
cluttered, and this shouldn't fire very often.

>   3. Select timeout value for the watchdog(s).
>
> Minor changes were made to watchdog code to accommodate this feature.
>
> Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx>
> Cc: Colin Cross <ccross@xxxxxxxxxxx>
> Cc: Todd Poynor <toddpoynor@xxxxxxxxxx>
> Cc: San Mehat <san@xxxxxxxxxx>
> Cc: Benoit Goby <benoit@xxxxxxxxxxx>
> Cc: John Stultz <john.stultz@xxxxxxxxxx>
> Cc: Pavel Machek <pavel@xxxxxx>
> Cc: Rafael J. Wysocki <rjw@xxxxxxx>
> Cc: Len Brown <len.brown@xxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Zoran Markovic <zoran.markovic@xxxxxxxxxx>

This whole patch is linked enough with the previous one that I suggest
squashing them together, and expanding your comments above your signed
off by to say you added configuration options.

> ---
>  drivers/base/power/main.c |   37 ++++++++++++++++++++++++++--------
>  kernel/power/Kconfig      |   48 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 77 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index a6a02c0..8e0bb33 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -392,6 +392,26 @@ static int dpm_run_callback(pm_callback_t cb, struct device *dev,
>         return error;
>  }
>
> +#ifdef CONFIG_DPM_WD
> +/**
> + * dpm_wd_action - recovery from suspend/resume watchdog timeout
> + * @wd: Watchdog. Must be allocated on the stack.
> + */
> +#if defined(CONFIG_DPM_WD_ACTION_STACKTRACE)
> +static inline void dpm_wd_action(struct dpm_watchdog *wd)
> +{
> +       show_stack(wd->tsk, NULL);
> +}
> +#elif defined(CONFIG_DPM_WD_ACTION_PANIC)
> +static inline void dpm_wd_action(struct dpm_watchdog *wd)
> +{
> +       panic("%s: unrecoverable failure\n", dev_name(wd->dev));

The panic here is not very useful, it's going to print the stack of
the task that was running when the timer fired which is likely to be
the idle task if the suspend task is deadlocked.  This should call
show_stack and panic.  If you take out the log action, then all this
can stay inline with the handler and be:

dev_emerg(wd->dev, "**** DPM device timeout ****\n");
show_stack(wd->tsk, NULL);
#ifdef CONFIG_DPM_WD_ACTION_PANIC
panic("%s: unrecoverable failure\n", dev_name(wd->dev));
#endif

Also, and this is a problem with the existing patch and not your
modifications, the format devname: error in the log is usually printed
by the device driver, which may cause confusion for someone who sees
this error and tries to grep for it in the mentioned driver.  Maybe a
better format for the pr_emerg and the panic would be:
   PM: **** DPM device timeout suspending devname ****
Ideally the message would specify if the error happened while
suspending or resuming.

> +}
> +#else /* CONFIG_DPM_WD_ACTION_LOG */
> +/* event already logged in dpm_wd_handler() */
> +#define dpm_wd_action(x)
> +#endif
> +
>  /**
>   * dpm_wd_handler - Driver suspend / resume watchdog handler.
>   *
> @@ -402,13 +422,9 @@ static int dpm_run_callback(pm_callback_t cb, struct device *dev,
>  static void dpm_wd_handler(unsigned long data)
>  {
>         struct dpm_watchdog *wd = (void *)data;
> -       struct device *dev      = wd->dev;
> -       struct task_struct *tsk = wd->tsk;
> -
> -       dev_emerg(dev, "**** DPM device timeout ****\n");
> -       show_stack(tsk, NULL);
>
> -       BUG();
> +       dev_emerg(wd->dev, "**** DPM device timeout ****\n");
> +       dpm_wd_action(wd);
>  }
>
>  /**
> @@ -424,14 +440,15 @@ static void dpm_wd_set(struct dpm_watchdog *wd, struct device *dev)
>         wd->tsk = get_current();
>
>         init_timer_on_stack(timer);
> -       timer->expires = jiffies + HZ * 12;
> +       /* use same timeout value for both suspend and resume */
> +       timer->expires = jiffies + HZ * CONFIG_DPM_WD_TIMEOUT;
>         timer->function = dpm_wd_handler;
>         timer->data = (unsigned long)wd;
>         add_timer(timer);
>  }
>
>  /**
> - * dpm_wd_clear - Disable pm watchdog.
> + * dpm_wd_clear - Disable suspend/resume watchdog.
>   * @wd: Watchdog to disable.
>   */
>  static void dpm_wd_clear(struct dpm_watchdog *wd)
> @@ -441,6 +458,10 @@ static void dpm_wd_clear(struct dpm_watchdog *wd)
>         del_timer_sync(timer);
>         destroy_timer_on_stack(timer);
>  }
> +#else
> +#define dpm_wd_set(x, y)
> +#define dpm_wd_clear(x)
> +#endif
>
>  /*------------------------- Resume routines -------------------------*/
>
> diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
> index edc8bdd..339caa1 100644
> --- a/kernel/power/Kconfig
> +++ b/kernel/power/Kconfig
> @@ -179,6 +179,54 @@ config PM_SLEEP_DEBUG
>         def_bool y
>         depends on PM_DEBUG && PM_SLEEP
>
> +config DPM_WD
> +       bool "Device suspend/resume watchdog"
> +       depends on PM_DEBUG
> +       ---help---
> +         Sets up a watchdog timer to capture drivers that are
> +         locked up attempting to suspend/resume a device.
> +         A detected lockup causes a configurable watchdog action,
> +         such as logging the event, dumping the stack trace or
> +         kernel panic.
> +
> +choice
> +       prompt "Watchdog recovery action"
> +       default DPM_WD_ACTION_PANIC
> +       depends on DPM_WD
> +       ---help---
> +         Select recovery action triggered by suspend/resume watchdog.
> +
> +config DPM_WD_ACTION_PANIC
> +       bool "System panic"
> +       ---help---
> +         When selected, a lockup during device's suspend or
> +         resume would cause a system panic. This would immediately
> +         capture user's attention. Panic message can be observed in
> +         subsequent boot session using pstore.
> +
> +config DPM_WD_ACTION_STACKTRACE
> +       bool "Dump stack"
> +       ---help---
> +         When selected, a lockup during device's suspend or
> +         resume would cause the caller's stack to be
> +         captured in the system log. The stack trace shows
> +         which driver call caused a lockup.
> +
> +config DPM_WD_ACTION_LOG
> +       bool "Log event"
> +       ---help---
> +         When selected, a lockup during device's suspend or
> +         resume would cause the watchdog timeout event to be
> +         logged in the system log.
> +
> +endchoice
> +
> +config DPM_WD_TIMEOUT
> +       int "Watchdog timeout in seconds"
> +       range 1 120
> +       default 12
> +       depends on DPM_WD
> +
>  config PM_TRACE
>         bool
>         help
> --
> 1.7.9.5
>
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