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 while trying to debug an issue. Here we extend the existing debugfs variable to bind a timer to the written value N, so that it will reset every N minutes, 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. Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Paul Gortmaker <[email protected]> --- .../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..8d058bbc0859 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 60 > /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 53088219d7df..e3a462e39062 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -636,6 +636,7 @@ EXPORT_SYMBOL(__warn_printk); /* Support resetting WARN*_ONCE state */ static u64 clear_warn_once; +static bool warn_timer_active; static void do_clear_warn_once(void) { @@ -643,6 +644,14 @@ 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 + clear_warn_once * HZ * 60; + add_timer(timer); +} +static DEFINE_TIMER(warn_reset_timer, timer_warn_once); + static int warn_once_get(void *data, u64 *val) { *val = clear_warn_once; @@ -653,6 +662,29 @@ static int warn_once_set(void *data, u64 val) { clear_warn_once = val; + if (val > 1) { /* set/reset new timer */ + unsigned long expires = jiffies + val * HZ * 60; + + 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; + } + clear_warn_once = 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; } -- 2.17.1
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