Re: [PATCH v11 1/2] hung_task: Reset warning budget when problem gets resolved

[Bradley Morgan <brads@mainlining.org>]

On 4 October 2026 17:36:09 BST, Aaron Tomlin <atomlin@atomlin.com> wrote:
>The sysctl hung_task_warnings currently holds both the configured warning
>limit and the remaining budget. Each detailed report decrements the
>sysctl, so once it reaches zero, the configured limit is lost and cannot
>be restored automatically.
>
>Keep sysctl_hung_task_warnings as the configured warning limit and make
>khungtaskd the sole owner of the remaining budget. A check that finds no
>hung tasks reloads the budget directly from the configured limit. A
>successful sysctl write publishes an atomic reset request, which
>khungtaskd consumes at the start of the next check.
>
>Suggested-by: Petr Mladek <pmladek@suse.com>
>Suggested-by: Lance Yang <lance.yang@linux.dev>
>Tested-by: Lance Yang <lance.yang@linux.dev>
>Reviewed-by: Lance Yang <lance.yang@linux.dev>

LGTM:

Reviewed-by: Bradley Morgan <brads@mainlining.org>

>Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
>---
> Documentation/admin-guide/sysctl/kernel.rst |  5 ++-
> kernel/hung_task.c                          | 49 +++++++++++++++++----
> 2 files changed, 44 insertions(+), 10 deletions(-)
>
>diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
>index ffea61d448eb..c03369e234a9 100644
>--- a/Documentation/admin-guide/sysctl/kernel.rst
>+++ b/Documentation/admin-guide/sysctl/kernel.rst
>@@ -459,8 +459,9 @@ hung_task_warnings
> ==================
> 
> The maximum number of warnings to report. During a check interval
>-if a hung task is detected, this value is decreased by 1.
>-When this value reaches 0, no more warnings will be reported.
>+if a hung task is detected, the internal warning budget is decreased by 1.
>+When this budget reaches 0, no more detailed warnings will be reported. The
>+warning budget is reset to the configured limit when no hung task is found.
> This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
> 
> -1: report an infinite number of warnings.
>diff --git a/kernel/hung_task.c b/kernel/hung_task.c
>index 6fcc94ce4ca9..a5043188456d 100644
>--- a/kernel/hung_task.c
>+++ b/kernel/hung_task.c
>@@ -57,8 +57,20 @@ unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_
>  */
> static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
> 
>+/*
>+ * Limit the number of printed hung tasks to prevent printing
>+ * the same or similar backtraces repeatedly.
>+ */
> static int __read_mostly sysctl_hung_task_warnings = 10;
> 
>+/*
>+ * The number of hung tasks which still can be reported.
>+ * The budget gets restored to the original limit when
>+ * the previous stall is resolved.
>+ */
>+static int hung_task_warnings_budget = 10;
>+static atomic_t reset_hung_task_warnings = ATOMIC_INIT(0);
>+
> static int __read_mostly did_panic;
> static bool hung_task_call_panic;
> 
>@@ -245,11 +257,11 @@ static void hung_task_info(struct task_struct *t, unsigned long timeout,
> 	/*
> 	 * The given task did not get scheduled for more than
> 	 * CONFIG_DEFAULT_HUNG_TASK_TIMEOUT. Therefore, complain
>-	 * accordingly
>+	 * accordingly with full details if the budget is not exhausted.
> 	 */
>-	if (sysctl_hung_task_warnings || hung_task_call_panic) {
>-		if (sysctl_hung_task_warnings > 0)
>-			sysctl_hung_task_warnings--;
>+	if (hung_task_warnings_budget || hung_task_call_panic) {
>+		if (hung_task_warnings_budget > 0)
>+			hung_task_warnings_budget--;
> 		pr_err("INFO: task %s:%d blocked%s for more than %ld seconds.\n",
> 		       t->comm, t->pid, t->in_iowait ? " in I/O wait" : "",
> 		       (jiffies - t->last_switch_time) / HZ);
>@@ -264,7 +276,7 @@ static void hung_task_info(struct task_struct *t, unsigned long timeout,
> 		sched_show_task(t);
> 		debug_show_blocker(t, timeout);
> 
>-		if (!sysctl_hung_task_warnings)
>+		if (!hung_task_warnings_budget)
> 			pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
> 	}
> 
>@@ -304,7 +316,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> 	unsigned long last_break = jiffies;
> 	struct task_struct *g, *t;
> 	unsigned long this_round_count;
>-	int need_warning = sysctl_hung_task_warnings;
>+	int need_warning;
> 	unsigned long si_mask = hung_task_si_mask;
> 
> 	/*
>@@ -314,6 +326,11 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> 	if (test_taint(TAINT_DIE) || did_panic)
> 		return;
> 
>+	if (atomic_xchg_acquire(&reset_hung_task_warnings, 0))
>+		hung_task_warnings_budget =
>+			READ_ONCE(sysctl_hung_task_warnings);
>+	need_warning = hung_task_warnings_budget;
>+
> 	this_round_count = 0;
> 	rcu_read_lock();
> 	for_each_process_thread(g, t) {
>@@ -340,8 +357,11 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>  unlock:
> 	rcu_read_unlock();
> 
>-	if (!this_round_count)
>+	if (!this_round_count) {
>+		hung_task_warnings_budget =
>+			READ_ONCE(sysctl_hung_task_warnings);
> 		return;
>+	}
> 
> 	if (need_warning || hung_task_call_panic) {
> 		si_mask |= SYS_INFO_LOCKS;
>@@ -425,6 +445,19 @@ static int proc_dohung_task_timeout_secs(const struct ctl_table *table, int writ
> 	return ret;
> }
> 
>+static int proc_dohung_task_warnings(const struct ctl_table *table, int write,
>+				     void *buffer,
>+				     size_t *lenp, loff_t *ppos)
>+{
>+	int ret;
>+
>+	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
>+	if (!ret && write)
>+		atomic_set_release(&reset_hung_task_warnings, 1);
>+
>+	return ret;
>+}
>+
> /*
>  * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
>  * and hung_task_check_interval_secs
>@@ -480,7 +513,7 @@ static const struct ctl_table hung_task_sysctls[] = {
> 		.data		= &sysctl_hung_task_warnings,
> 		.maxlen		= sizeof(int),
> 		.mode		= 0644,
>-		.proc_handler	= proc_dointvec_minmax,
>+		.proc_handler	= proc_dohung_task_warnings,
> 		.extra1		= SYSCTL_NEG_ONE,
> 	},
> 	{
>


--- Thanks!
"I'm not a very positive person" - Linus torvalds