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

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear RongQing,


Thank you for the patch. One minor comment regarding the Kconfig 
description.

Am 15.10.25 um 08:36 schrieb lirongqing:
> From: Li RongQing <lirongqing@baidu.com>
> 
> 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.
> 
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> Cc: Andrew Jeffery <andrew@codeconstruct.com.au>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Florian Wesphal <fw@strlen.de>
> Cc: Jakub Kacinski <kuba@kernel.org>
> Cc: Jason A. Donenfeld <jason@zx2c4.com>
> Cc: Joel Granados <joel.granados@kernel.org>
> Cc: Joel Stanley <joel@jms.id.au>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Kees Cook <kees@kernel.org>
> Cc: Lance Yang <lance.yang@linux.dev>
> Cc: Liam Howlett <liam.howlett@oracle.com>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
> Cc: "Paul E . McKenney" <paulmck@kernel.org>
> Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: Phil Auld <pauld@redhat.com>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Simon Horman <horms@kernel.org>
> Cc: Stanislav Fomichev <sdf@fomichev.me>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> ---
> 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/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
Why not leave the sentence about the uninterruptible "D" state in there?

Also, it sounds like, some are actually using this in production. Maybe 
it should be moved out of `Kconfig.debug` too?


Kind regards,

Paul