Existing documentation has a write of "1" to clear/reset all the
WARN_ONCE and similar to the as-booted state, so they can possibly
be re-triggered again during debugging/testing.
But having them auto-reset once a day, or once a week, might shed
valuable information to a sysadmin on what the system is doing.
Here we extend the existing debugfs variable to bind a timer to the
written value N, so that it will reset every N seconds, for N>1.
Writing a zero will clear any previously set timer value.
The pre-existing behaviour of writing N=1 will do a one-shot clear.
Cc: Andi Kleen <a...@linux.intel.com>
Cc: Petr Mladek <pmla...@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: John Ogness <john.ogn...@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortma...@windriver.com>
---
.../admin-guide/clearing-warn-once.rst | 9 ++++++
kernel/panic.c | 32 +++++++++++++++++++
2 files changed, 41 insertions(+)
diff --git a/Documentation/admin-guide/clearing-warn-once.rst
b/Documentation/admin-guide/clearing-warn-once.rst
index 211fd926cf00..93cf3ba0b57d 100644
--- a/Documentation/admin-guide/clearing-warn-once.rst
+++ b/Documentation/admin-guide/clearing-warn-once.rst
@@ -7,3 +7,12 @@ echo 1 > /sys/kernel/debug/clear_warn_once
clears the state and allows the warnings to print once again.
This can be useful after test suite runs to reproduce problems.
+
+Values greater than one set a timer for a periodic state reset; e.g.
+
+echo 3600 > /sys/kernel/debug/clear_warn_once
+
+will establish an hourly state reset, effectively turning WARN_ONCE
+into a long period rate-limited warning.
+
+Writing a value of zero (or one) will remove any previously set timer.
diff --git a/kernel/panic.c b/kernel/panic.c
index 1d425970a50c..a23eb239fb17 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -655,6 +655,7 @@ EXPORT_SYMBOL(__warn_printk);
/* Support resetting WARN*_ONCE state */
static u64 warn_once_reset;
+static bool warn_timer_active;
static void do_clear_warn_once(void)
{
@@ -662,6 +663,14 @@ static void do_clear_warn_once(void)
memset(__start_once, 0, __end_once - __start_once);
}
+static void timer_warn_once(struct timer_list *timer)
+{
+ do_clear_warn_once();
+ timer->expires = jiffies + warn_once_reset * HZ;
+ add_timer(timer);
+}
+static DEFINE_TIMER(warn_reset_timer, timer_warn_once);
+
static int warn_once_get(void *data, u64 *val)
{
*val = warn_once_reset;
@@ -672,6 +681,29 @@ static int warn_once_set(void *data, u64 val)
{
warn_once_reset = val;
+ if (val > 1) { /* set/reset new timer */
+ unsigned long expires = jiffies + val * HZ;
+
+ if (warn_timer_active) {
+ mod_timer(&warn_reset_timer, expires);
+ } else {
+ warn_timer_active = 1;
+ warn_reset_timer.expires = expires;
+ add_timer(&warn_reset_timer);
+ }
+ return 0;
+ }
+
+ if (warn_timer_active) {
+ del_timer_sync(&warn_reset_timer);
+ warn_timer_active = 0;
+ }
+ warn_once_reset = 0;
+
+ if (val == 0) /* cleared timer, we are done */
+ return 0;
+
+ /* Getting here means val == 1 ---> so clear existing data */
do_clear_warn_once();
return 0;
}
--
2.25.1
