On 1/27/21 5:14 PM, JP Ertola wrote:
> If the watchdog timeout is set such that the crash kernel does not
> have time to collect a coredump and the crash kernel is not equipped to
> ping the watchdog timer itself, then a kernel coredump will not be collected
> before the watchdog fires. This change registers a panic notifier and
> callback so the watchdog timeout can be extended if a kernel panic occurs.
> This timeout extension would give the crash kernel enough time to collect
> a coredump before the CPU resets. The watchdog timeout is extended if and only
> if a crash kernel image is loaded in memory and the watchdog is active at the
> time of the panic.
>
> Drivers have the option of implementing their own platform-dependent (PD)
> callback at the same time they register their watchdog device (wdd) with the
> Linux kernel. By registering their own PD callback, the watchdog device
> can extend the watchdog timeout and perform other tasks in a panic context.
>
> This may be desireable when uncommon hardware platforms are used. For
> example, a power management subsystem controlled by an FPGA attached to
> the CPU.
This is only acceptable if there is an actual user for this callback.
I won't accept adding such a callback without a user. If you have one
in mind, please submit the patch adding it as part of a series.
That will let us evaluate if the callback is really needed and
what it is used for. Otherwise, please drop the callback.
>
> A Kconfig option has been added to configure the timeout duration at
> compile-time. Default is zero seconds.
>
> Signed-off-by: JP Ertola <jp.ertola@xxxxxxx>
> ---
Change log goes here, and I am not going back to v2 and v1 to try to figure
out what changed.
Guenter
> drivers/watchdog/Kconfig | 13 +++++
> drivers/watchdog/watchdog_dev.c | 84 ++++++++++++++++++++++++++++++++-
> include/linux/watchdog.h | 3 ++
> 3 files changed, 99 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index fd7968635e6d..f1055985e100 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -141,6 +141,19 @@ comment "Watchdog Device Drivers"
>
> # Architecture Independent
>
> +config DEFAULT_WATCHDOG_CRASH_KERNEL_TIMEOUT
> + int "Default timeout for watchdog timer before crash kernel starts (seconds)"
> + default 0
> + help
> + This option allows an extended timeout to be used for the watchdog when
> + the kernel panics and a crash kernel is about to start. This is helpful
> + when the existing WDT timeout value is less than the time required for
> + crash kernel to run and the crash kernel is unable to handle the
> + the watchdog itself. The timeout extension happens last in chain of
> + kernel panic handler callbacks just in case another panic handler
> + hangs unexpectedly. When this value is set to 0, the watchdog timeout
> + will not be changed.
> +
> config SOFT_WATCHDOG
> tristate "Software watchdog"
> select WATCHDOG_CORE
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 2946f3a63110..e2d056c70ca7 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -34,6 +34,7 @@
> #include <linux/init.h> /* For __init/__exit/... */
> #include <linux/hrtimer.h> /* For hrtimers */
> #include <linux/kernel.h> /* For printk/panic/... */
> +#include <linux/kexec.h> /* For checking if crash kernel is loaded */
> #include <linux/kthread.h> /* For kthread_work */
> #include <linux/miscdevice.h> /* For handling misc devices */
> #include <linux/module.h> /* For module stuff/... */
> @@ -82,6 +83,8 @@ static bool handle_boot_enabled =
>
> static unsigned open_timeout = CONFIG_WATCHDOG_OPEN_TIMEOUT;
>
> +static unsigned int wdt_panic_timeout = CONFIG_DEFAULT_WATCHDOG_CRASH_KERNEL_TIMEOUT;
> +
> static bool watchdog_past_open_deadline(struct watchdog_core_data *data)
> {
> return ktime_after(ktime_get(), data->open_deadline);
> @@ -658,6 +661,61 @@ static int watchdog_ioctl_op(struct watchdog_device *wdd, unsigned int cmd,
> * off the watchdog (if 'nowayout' is not set).
> */
>
> +static int watchdog_panic_notifier(struct notifier_block *nb,
> + unsigned long code, void *data)
> +{
> + struct watchdog_device *wdd;
> + int ret = 0;
> + unsigned int time_out = 0; // seconds
> +
> + if (wdt_panic_timeout == 0)
> + return NOTIFY_DONE;
> +
> + if (watchdog_timeout_invalid(wdt_panic_timeout)) {
> + time_out = min(wdt_panic_timeout, wdd->max_timeout);
> + pr_err("watchdog%d: timeout extension value "
> + " invalid. Falling back to %d seconds\n", time_out);
> + } else {
> + time_out = wdt_panic_timeout;
> + }
> +
> + wdd = container_of(nb, struct watchdog_device, panic_nb);
> +
> + if (kexec_crash_image && watchdog_active(wdd)) {
> + if (wdd->ops->panic_cb) {
> + ret = wdd->ops->panic_cb(wdd, time_out);
> + } else {
> + int ping_ret;
> +
> + pr_info("watchdog%d: Extending watchdog timeout to "
> + "%d seconds\n", wdd->id, time_out);
> +
> + ret = watchdog_set_timeout(wdd, time_out);
> +
> + /* Many watchdog implementations will reset the timer
> + * when the timeout is changed, but ping again to be
> + * safe.
> + */
> + if (wdd->ops->ping) {
> + ping_ret = wdd->ops->ping(wdd);
> + if (ping_ret) {
> + pr_warn("watchdog%d: Unable to ping "
> + "watchdog before starting "
> + "crash kernel (%d)\n",
> + wdd->id, ping_ret);
> + }
> + }
> + }
> + if (ret) {
> + pr_err("watchdog%d: Unable to extend watchdog timeout "
> + "before starting crash kernel (%d)",
> + wdd->id, ret);
> + }
> + }
> +
> + return notifier_from_errno(ret);
> +}
> +
> static ssize_t watchdog_write(struct file *file, const char __user *data,
> size_t len, loff_t *ppos)
> {
> @@ -1118,8 +1176,27 @@ int watchdog_dev_register(struct watchdog_device *wdd)
> return ret;
>
> ret = watchdog_register_pretimeout(wdd);
> - if (ret)
> + if (ret) {
> watchdog_cdev_unregister(wdd);
> + return ret;
> + }
> +
> + /*
> + * Setting panic_nb priority to minimum ensures the watchdog device
> + * panic callback runs last in the chain of kernel panic callbacks.
> + * This way, the watchdog device will fire in the event another
> + * panic callback hangs.
> + */
> + if (wdd->ops->panic_cb) {
> + wdd->panic_nb.priority = INT_MIN;
> + wdd->panic_nb.notifier_call = watchdog_panic_notifier;
> +
> + ret = atomic_notifier_chain_register(&panic_notifier_list,
> + &wdd->panic_nb);
> + if (ret)
> + pr_err("watchdog%d: Cannot register panic notifier (%d)\n",
> + wdd->id, ret);
> + }
>
> return ret;
> }
> @@ -1228,3 +1305,8 @@ module_param(open_timeout, uint, 0644);
> MODULE_PARM_DESC(open_timeout,
> "Maximum time (in seconds, 0 means infinity) for userspace to take over a running watchdog (default="
> __MODULE_STRING(CONFIG_WATCHDOG_OPEN_TIMEOUT) ")");
> +
> +module_param(wdt_panic_timeout, uint, 0444);
> +MODULE_PARM_DESC(wdt_panic_timeout,
> + "Watchdog timeout extension duration upon kernel panic. (default="
> + __MODULE_STRING(CONFIG_DEFAULT_WATCHDOG_CRASH_KERNEL_TIMEOUT) " seconds)");
> diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
> index 9b19e6bb68b5..f79f41cca156 100644
> --- a/include/linux/watchdog.h
> +++ b/include/linux/watchdog.h
> @@ -34,6 +34,7 @@ struct watchdog_governor;
> * @get_timeleft:The routine that gets the time left before a reset (in seconds).
> * @restart: The routine for restarting the machine.
> * @ioctl: The routines that handles extra ioctl calls.
> + * @panic_cb: The routine that extends the watchdog timeout before the crash kernel starts.
> *
> * The watchdog_ops structure contains a list of low-level operations
> * that control a watchdog device. It also contains the module that owns
> @@ -53,6 +54,7 @@ struct watchdog_ops {
> unsigned int (*get_timeleft)(struct watchdog_device *);
> int (*restart)(struct watchdog_device *, unsigned long, void *);
> long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
> + int (*panic_cb)(struct watchdog_device *, unsigned int);
> };
>
> /** struct watchdog_device - The structure that defines a watchdog device
> @@ -107,6 +109,7 @@ struct watchdog_device {
> unsigned int max_hw_heartbeat_ms;
> struct notifier_block reboot_nb;
> struct notifier_block restart_nb;
> + struct notifier_block panic_nb;
> void *driver_data;
> struct watchdog_core_data *wd_data;
> unsigned long status;
>
