Re: [PATCH] hung_task: Panic after fixed number of hung tasks

Lance Yang
2025-09-27T02:39:17Z

On 2025/9/25 14:06, lirongqing wrote:
> From: Li RongQing <lirongqing@baidu.com>
>
> Currently, when hung_task_panic is enabled, kernel will panic immediately
> upon detecting the first hung task. However, some hung tasks are transient
> and the system can recover fully, while others are unrecoverable and
> trigger consecutive hung task reports, and a panic is expected.
>
> This commit adds a new sysctl parameter hung_task_count_to_panic to allows
> specifying the number of consecutive hung tasks that must be detected
> before triggering a kernel panic. This provides finer control for
> environments where transient hangs maybe happen but persistent hangs should
> still be fatal.
>
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> ---
> Documentation/admin-guide/sysctl/kernel.rst | 6 ++++++
> kernel/hung_task.c | 14 +++++++++++++-
> 2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index 8b49eab..4240e7b 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -405,6 +405,12 @@ This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
> 1 Panic immediately.
> = =================================================
>
> +hung_task_count_to_panic
> +=====================
> +
> +When set to a non-zero value, after the number of consecutive hung task
> +occur, the kernel will triggers a panic

Hmm... the documentation here seems a bit misleading.

hung_task_panic=1 will always cause an immediate panic, regardless of
the hung_task_count_to_panic setting, right?

Perhaps something like this would be more accurate?

```
hung_task_count_to_panic
========================

When set to a non-zero value, a kernel panic will be triggered if
the number of detected hung tasks reaches this value.

Note that setting hung_task_panic=1 will still cause an immediate
panic on the first hung task, overriding this setting.
```

>
> hung_task_check_count
> =====================
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 8708a12..87a6421 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -83,6 +83,8 @@ static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
> static unsigned int __read_mostly sysctl_hung_task_panic =
> IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
>
> +static unsigned int __read_mostly sysctl_hung_task_count_to_panic;

Nit: while static variables are guaranteed to be zero-initialized, it's
a good practice and clearer for readers to initialize them explicitly.

static unsigned int __read_mostly sysctl_hung_task_count_to_panic = 0;

Otherwise, this patch looks good to me!
Acked-by: Lance Yang <lance.yang@linux.dev>

> +
> static int
> hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
> {
> @@ -219,7 +221,9 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
>
> trace_sched_process_hang(t);
>
> - if (sysctl_hung_task_panic) {
> + if (sysctl_hung_task_panic ||
> + (sysctl_hung_task_count_to_panic &&
> + (sysctl_hung_task_detect_count >= sysctl_hung_task_count_to_panic))) {
> console_verbose();
> hung_task_show_lock = true;
> hung_task_call_panic = true;
> @@ -388,6 +392,14 @@ static const struct ctl_table hung_task_sysctls[] = {
> .extra2 = SYSCTL_ONE,
> },
> {
> + .procname = "hung_task_count_to_panic",
> + .data = &sysctl_hung_task_count_to_panic,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = SYSCTL_ZERO,
> + },
> + {
> .procname = "hung_task_check_count",
> .data = &sysctl_hung_task_check_count,
> .maxlen = sizeof(int),