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

lirongqing
2025-11-19T21:44:57Z

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/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