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

[Lance Yang]

On 2025/9/25 14:06, lirongqing wrote:
> From: Li RongQing <lirongqing@xxxxxxxxx>
>
> 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@xxxxxxxxx>
> ---
>   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@xxxxxxxxx>

> +
>   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),