[PATCH 3/3] Test softlockup

[Petr Mladek]

Trigger busy loop by:
$> cat /proc/version

Stop the busy loop by:
$> cat /proc/console

The code also shows the first touch*watchdog() function that hides
softlockup on a "well known" location.

Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
---
 fs/proc/consoles.c |  5 +++++
 fs/proc/version.c  |  7 +++++++
 kernel/watchdog.c  | 25 ++++++++++++++++++++++++-
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/fs/proc/consoles.c b/fs/proc/consoles.c
index 954caf0b7fee..288ac1ab33c6 100644
--- a/fs/proc/consoles.c
+++ b/fs/proc/consoles.c
@@ -10,6 +10,8 @@
 #include <linux/seq_file.h>
 #include <linux/tty_driver.h>
 
+extern volatile bool proc_version_wait;
+
 /*
  * This is handler for /proc/consoles
  */
@@ -31,6 +33,9 @@ static int show_console_dev(struct seq_file *m, void *v)
 	unsigned int a;
 	dev_t dev = 0;
 
+	printk("%s: Going to break /proc/version infinite loop\n", __func__);
+	proc_version_wait = false;
+
 	if (con->device) {
 		const struct tty_driver *driver;
 		int index;
diff --git a/fs/proc/version.c b/fs/proc/version.c
index b449f186577f..15ec6a502589 100644
--- a/fs/proc/version.c
+++ b/fs/proc/version.c
@@ -6,8 +6,15 @@
 #include <linux/seq_file.h>
 #include <linux/utsname.h>
 
+volatile bool proc_version_wait;
+
 static int version_proc_show(struct seq_file *m, void *v)
 {
+	printk("%s: Going to wait until stopped\n", __func__);
+	proc_version_wait = true;
+	while (proc_version_wait)
+		cpu_relax();
+
 	seq_printf(m, linux_proc_banner,
 		utsname()->sysname,
 		utsname()->release,
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 2058229ed398..3bfe6fbc468b 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -172,6 +172,7 @@ static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
 static DEFINE_PER_CPU(unsigned long, watchdog_period_ts);
 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 static DEFINE_PER_CPU(bool, watchdog_restart_period);
+static DEFINE_PER_CPU(bool, watchdog_report_restart_period);
 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
@@ -259,6 +260,7 @@ static void __restart_watchdog_period(void)
 {
 	__this_cpu_write(watchdog_period_ts, get_timestamp());
 	__this_cpu_write(watchdog_restart_period, false);
+	__this_cpu_write(watchdog_report_restart_period, false);
 }
 
 /* Commands for resetting the watchdog */
@@ -283,6 +285,13 @@ notrace void touch_softlockup_watchdog_sched(void)
 	 * period gets restarted here, so use the raw_ operation.
 	 */
 	raw_cpu_write(watchdog_restart_period, true);
+
+	if (raw_cpu_read(watchdog_report_restart_period)) {
+		printk_deferred("Softlockup watchdog need reset from %s\n",
+			__func__);
+		trace_dump_stack(0);
+		raw_cpu_write(watchdog_report_restart_period, false);
+	}
 }
 
 notrace void touch_softlockup_watchdog(void)
@@ -305,8 +314,15 @@ void touch_all_softlockup_watchdogs(void)
 	 * update as well, the only side effect might be a cycle delay for
 	 * the softlockup check.
 	 */
-	for_each_cpu(cpu, &watchdog_allowed_mask)
+	for_each_cpu(cpu, &watchdog_allowed_mask) {
 		per_cpu(watchdog_restart_period, cpu) = true;
+
+		if (per_cpu(watchdog_report_restart_period, cpu) == true) {
+			WARN(1, "Softlockup watchdog need reset\n");
+			per_cpu(watchdog_report_restart_period, cpu) = false;
+		}
+	}
+
 	wq_watchdog_touch(-1);
 }
 
@@ -314,6 +330,11 @@ void touch_softlockup_watchdog_sync(void)
 {
 	__this_cpu_write(softlockup_touch_sync, true);
 	__this_cpu_write(watchdog_restart_period, true);
+
+	if (raw_cpu_read(watchdog_report_restart_period)) {
+		WARN(1, "Softlockup watchdog need reset\n");
+		raw_cpu_write(watchdog_report_restart_period, false);
+	}
 }
 
 static int is_softlockup(unsigned long touch_ts, unsigned long period_ts)
@@ -461,6 +482,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 		if (softlockup_panic)
 			panic("softlockup: hung tasks");
+
+		__this_cpu_write(watchdog_report_restart_period, true);
 	}
 
 	return HRTIMER_RESTART;
-- 
2.16.4