PM: sleep: Allow configuring the DPM watchdog to warn earlier than panic

Allow configuring the DPM watchdog to warn about slow suspend/resume
functions without causing a system panic(). This allows you to set the
DPM_WATCHDOG_WARNING_TIMEOUT to something like 5 or 10 seconds to get
warnings about slow suspend/resume functions that eventually succeed.

Signed-off-by: Douglas Anderson <[email protected]>
Reviewed-by: Tomasz Figa <[email protected]>
Link: https://patch.msgid.link/20250109125957.v2.1.I4554f931b8da97948f308ecc651b124338ee9603@changeid
[ rjw: Subject edit ]
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: dianders

drivers/base/power/main.c

@@ -496,6 +496,7 @@ struct dpm_watchdog {
 	struct device		*dev;
 	struct task_struct	*tsk;
 	struct timer_list	timer;
+	bool			fatal;
 };
 
 #define DECLARE_DPM_WATCHDOG_ON_STACK(wd) \
@@ -512,11 +513,23 @@ struct dpm_watchdog {
 static void dpm_watchdog_handler(struct timer_list *t)
 {
 	struct dpm_watchdog *wd = from_timer(wd, t, timer);
+	struct timer_list *timer = &wd->timer;
+	unsigned int time_left;
+
+	if (wd->fatal) {
+		dev_emerg(wd->dev, "**** DPM device timeout ****\n");
+		show_stack(wd->tsk, NULL, KERN_EMERG);
+		panic("%s %s: unrecoverable failure\n",
+			dev_driver_string(wd->dev), dev_name(wd->dev));
+	}
+
+	time_left = CONFIG_DPM_WATCHDOG_TIMEOUT - CONFIG_DPM_WATCHDOG_WARNING_TIMEOUT;
+	dev_warn(wd->dev, "**** DPM device timeout after %u seconds; %u seconds until panic ****\n",
+		 CONFIG_DPM_WATCHDOG_WARNING_TIMEOUT, time_left);
+	show_stack(wd->tsk, NULL, KERN_WARNING);
 
-	dev_emerg(wd->dev, "**** DPM device timeout ****\n");
-	show_stack(wd->tsk, NULL, KERN_EMERG);
-	panic("%s %s: unrecoverable failure\n",
-		dev_driver_string(wd->dev), dev_name(wd->dev));
+	wd->fatal = true;
+	mod_timer(timer, jiffies + HZ * time_left);
 }
 
 /**
@@ -530,10 +543,11 @@ static void dpm_watchdog_set(struct dpm_watchdog *wd, struct device *dev)
 
 	wd->dev = dev;
 	wd->tsk = current;
+	wd->fatal = CONFIG_DPM_WATCHDOG_TIMEOUT == CONFIG_DPM_WATCHDOG_WARNING_TIMEOUT;
 
 	timer_setup_on_stack(timer, dpm_watchdog_handler, 0);
 	/* use same timeout value for both suspend and resume */
-	timer->expires = jiffies + HZ * CONFIG_DPM_WATCHDOG_TIMEOUT;
+	timer->expires = jiffies + HZ * CONFIG_DPM_WATCHDOG_WARNING_TIMEOUT;
 	add_timer(timer);
 }
 

kernel/power/Kconfig

@@ -257,11 +257,30 @@ config DPM_WATCHDOG
 	  boot session.
 
 config DPM_WATCHDOG_TIMEOUT
-	int "Watchdog timeout in seconds"
+	int "Watchdog timeout to panic in seconds"
 	range 1 120
 	default 120
 	depends on DPM_WATCHDOG
 
+config DPM_WATCHDOG_WARNING_TIMEOUT
+	int "Watchdog timeout to warn in seconds"
+	range 1 DPM_WATCHDOG_TIMEOUT
+	default DPM_WATCHDOG_TIMEOUT
+	depends on DPM_WATCHDOG
+	help
+	  If the DPM watchdog warning timeout and main timeout are
+	  different then a non-fatal warning (with a stack trace of
+	  the stuck suspend routine) will be printed when the warning
+	  timeout expires. If the suspend routine gets un-stuck
+	  before the main timeout expires then no other action is
+	  taken. If the routine continues to be stuck and the main
+	  timeout expires then an emergency-level message and stack
+	  trace will be printed and the system will panic.
+
+	  If the warning timeout is equal to the main timeout (the
+	  default) then the warning will never happen and the system
+	  will jump straight to panic when the main timeout expires.
+
 config PM_TRACE
 	bool
 	help