Re: [PATCH][v4] hung_task: Panic when there are more than N hung tasks at the same time

On Wed, 15 Oct 2025 14:36:15 +0800
lirongqing <[email protected]> wrote:

> From: Li RongQing <[email protected]>
> 
> Currently, when 'hung_task_panic' is enabled, the kernel panics
> immediately upon detecting the first hung task. However, some hung
> tasks are transient and allow system recovery, while persistent hangs
> should trigger a panic when accumulating beyond a threshold.
> 
> Extend the 'hung_task_panic' sysctl to accept a threshold value
> specifying the number of hung tasks that must be detected before
> triggering a kernel panic. This provides finer control for environments
> where transient hangs may occur but persistent hangs should be fatal.
> 
> The sysctl now accepts:
> - 0: don't panic (maintains original behavior)
> - 1: panic on first hung task (maintains original behavior)
> - N > 1: panic after N hung tasks are detected in a single scan
> 
> This maintains backward compatibility while providing flexibility for
> different hang scenarios.

Looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <[email protected]>

Thank you,

> 
> Signed-off-by: Li RongQing <[email protected]>
> Cc: Andrew Jeffery <[email protected]>
> Cc: Anshuman Khandual <[email protected]>
> Cc: Arnd Bergmann <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Florian Wesphal <[email protected]>
> Cc: Jakub Kacinski <[email protected]>
> Cc: Jason A. Donenfeld <[email protected]>
> Cc: Joel Granados <[email protected]>
> Cc: Joel Stanley <[email protected]>
> Cc: Jonathan Corbet <[email protected]>
> Cc: Kees Cook <[email protected]>
> Cc: Lance Yang <[email protected]>
> Cc: Liam Howlett <[email protected]>
> Cc: Lorenzo Stoakes <[email protected]>
> Cc: "Masami Hiramatsu (Google)" <[email protected]>
> Cc: "Paul E . McKenney" <[email protected]>
> Cc: Pawan Gupta <[email protected]>
> Cc: Petr Mladek <[email protected]>
> Cc: Phil Auld <[email protected]>
> Cc: Randy Dunlap <[email protected]>
> Cc: Russell King <[email protected]>
> Cc: Shuah Khan <[email protected]>
> Cc: Simon Horman <[email protected]>
> Cc: Stanislav Fomichev <[email protected]>
> Cc: Steven Rostedt <[email protected]>
> ---
> diff with v3: comments modification, suggested by Lance, Masami, Randy and Petr
> diff with v2: do not add a new sysctl, extend hung_task_panic, suggested by Kees Cook
> 
>  Documentation/admin-guide/kernel-parameters.txt      | 20 +++++++++++++-------
>  Documentation/admin-guide/sysctl/kernel.rst          |  9 +++++----
>  arch/arm/configs/aspeed_g5_defconfig                 |  2 +-
>  kernel/configs/debug.config                          |  2 +-
>  kernel/hung_task.c                                   | 15 ++++++++++-----
>  lib/Kconfig.debug                                    |  9 +++++----
>  tools/testing/selftests/wireguard/qemu/kernel.config |  2 +-
>  7 files changed, 36 insertions(+), 23 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index a51ab46..492f0bc 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1992,14 +1992,20 @@
>  			the added memory block itself do not be affected.
>  
>  	hung_task_panic=
> -			[KNL] Should the hung task detector generate panics.
> -			Format: 0 | 1
> +			[KNL] Number of hung tasks to trigger kernel panic.
> +			Format: <int>
> +
> +			When set to a non-zero value, a kernel panic will be triggered if
> +			the number of detected hung tasks reaches this value.
> +
> +			0: don't panic
> +			1: panic immediately on first hung task
> +			N: panic after N hung tasks are detected in a single scan
>  
> -			A value of 1 instructs the kernel to panic when a
> -			hung task is detected. The default value is controlled
> -			by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
> -			option. The value selected by this boot parameter can
> -			be changed later by the kernel.hung_task_panic sysctl.
> +			The default value is controlled by the
> +			CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value
> +			selected by this boot parameter can be changed later by the
> +			kernel.hung_task_panic sysctl.
>  
>  	hvc_iucv=	[S390]	Number of z/VM IUCV hypervisor console (HVC)
>  				terminal devices. Valid values: 0..8
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index f3ee807..0065a55 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -397,13 +397,14 @@ a hung task is detected.
>  hung_task_panic
>  ===============
>  
> -Controls the kernel's behavior when a hung task is detected.
> +When set to a non-zero value, a kernel panic will be triggered if the
> +number of hung tasks found during a single scan reaches this value.
>  This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
>  
> -= =================================================
> += =======================================================
>  0 Continue operation. This is the default behavior.
> -1 Panic immediately.
> -= =================================================
> +N Panic when N hung tasks are found during a single scan.
> += =======================================================
>  
>  
>  hung_task_check_count
> diff --git a/arch/arm/configs/aspeed_g5_defconfig b/arch/arm/configs/aspeed_g5_defconfig
> index 61cee1e..c3b0d5f 100644
> --- a/arch/arm/configs/aspeed_g5_defconfig
> +++ b/arch/arm/configs/aspeed_g5_defconfig
> @@ -308,7 +308,7 @@ CONFIG_PANIC_ON_OOPS=y
>  CONFIG_PANIC_TIMEOUT=-1
>  CONFIG_SOFTLOCKUP_DETECTOR=y
>  CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC=y
> -CONFIG_BOOTPARAM_HUNG_TASK_PANIC=y
> +CONFIG_BOOTPARAM_HUNG_TASK_PANIC=1
>  CONFIG_WQ_WATCHDOG=y
>  # CONFIG_SCHED_DEBUG is not set
>  CONFIG_FUNCTION_TRACER=y
> diff --git a/kernel/configs/debug.config b/kernel/configs/debug.config
> index e81327d..9f6ab7d 100644
> --- a/kernel/configs/debug.config
> +++ b/kernel/configs/debug.config
> @@ -83,7 +83,7 @@ CONFIG_SLUB_DEBUG_ON=y
>  #
>  # Debug Oops, Lockups and Hangs
>  #
> -# CONFIG_BOOTPARAM_HUNG_TASK_PANIC is not set
> +CONFIG_BOOTPARAM_HUNG_TASK_PANIC=0
>  # CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC is not set
>  CONFIG_DEBUG_ATOMIC_SLEEP=y
>  CONFIG_DETECT_HUNG_TASK=y
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index b2c1f14..84b4b04 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -81,7 +81,7 @@ static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
>   * hung task is detected:
>   */
>  static unsigned int __read_mostly sysctl_hung_task_panic =
> -	IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
> +	CONFIG_BOOTPARAM_HUNG_TASK_PANIC;
>  
>  static int
>  hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
> @@ -218,8 +218,11 @@ static inline void debug_show_blocker(struct task_struct *task, unsigned long ti
>  }
>  #endif
>  
> -static void check_hung_task(struct task_struct *t, unsigned long timeout)
> +static void check_hung_task(struct task_struct *t, unsigned long timeout,
> +		unsigned long prev_detect_count)
>  {
> +	unsigned long total_hung_task;
> +
>  	if (!task_is_hung(t, timeout))
>  		return;
>  
> @@ -229,9 +232,10 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
>  	 */
>  	sysctl_hung_task_detect_count++;
>  
> +	total_hung_task = sysctl_hung_task_detect_count - prev_detect_count;
>  	trace_sched_process_hang(t);
>  
> -	if (sysctl_hung_task_panic) {
> +	if (sysctl_hung_task_panic && total_hung_task >= sysctl_hung_task_panic) {
>  		console_verbose();
>  		hung_task_show_lock = true;
>  		hung_task_call_panic = true;
> @@ -300,6 +304,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>  	int max_count = sysctl_hung_task_check_count;
>  	unsigned long last_break = jiffies;
>  	struct task_struct *g, *t;
> +	unsigned long prev_detect_count = sysctl_hung_task_detect_count;
>  
>  	/*
>  	 * If the system crashed already then all bets are off,
> @@ -320,7 +325,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>  			last_break = jiffies;
>  		}
>  
> -		check_hung_task(t, timeout);
> +		check_hung_task(t, timeout, prev_detect_count);
>  	}
>   unlock:
>  	rcu_read_unlock();
> @@ -389,7 +394,7 @@ static const struct ctl_table hung_task_sysctls[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec_minmax,
>  		.extra1		= SYSCTL_ZERO,
> -		.extra2		= SYSCTL_ONE,
> +		.extra2		= SYSCTL_INT_MAX,
>  	},
>  	{
>  		.procname	= "hung_task_check_count",
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 3034e294..3976c90 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1258,12 +1258,13 @@ config DEFAULT_HUNG_TASK_TIMEOUT
>  	  Keeping the default should be fine in most cases.
>  
>  config BOOTPARAM_HUNG_TASK_PANIC
> -	bool "Panic (Reboot) On Hung Tasks"
> +	int "Number of hung tasks to trigger kernel panic"
>  	depends on DETECT_HUNG_TASK
> +	default 0
>  	help
> -	  Say Y here to enable the kernel to panic on "hung tasks",
> -	  which are bugs that cause the kernel to leave a task stuck
> -	  in uninterruptible "D" state.
> +	  When set to a non-zero value, a kernel panic will be triggered
> +	  if the number of hung tasks found during a single scan reaches
> +	  this value.
>  
>  	  The panic can be used in combination with panic_timeout,
>  	  to cause the system to reboot automatically after a
> diff --git a/tools/testing/selftests/wireguard/qemu/kernel.config b/tools/testing/selftests/wireguard/qemu/kernel.config
> index 936b18b..0504c11 100644
> --- a/tools/testing/selftests/wireguard/qemu/kernel.config
> +++ b/tools/testing/selftests/wireguard/qemu/kernel.config
> @@ -81,7 +81,7 @@ CONFIG_WQ_WATCHDOG=y
>  CONFIG_DETECT_HUNG_TASK=y
>  CONFIG_BOOTPARAM_HARDLOCKUP_PANIC=y
>  CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC=y
> -CONFIG_BOOTPARAM_HUNG_TASK_PANIC=y
> +CONFIG_BOOTPARAM_HUNG_TASK_PANIC=1
>  CONFIG_PANIC_TIMEOUT=-1
>  CONFIG_STACKTRACE=y
>  CONFIG_EARLY_PRINTK=y
> -- 
> 2.9.4
> 


-- 
Masami Hiramatsu (Google) <[email protected]>