RE: [外部邮件] Re: [PATCH][v3] hung_task: Panic after fixed number of hung tasks
Li,Rongqing
lirongqing at baidu.com
Tue Oct 14 16:33:07 AEDT 2025
>
> I noticed the implementation panics only when N tasks are detected within a
> single scan, because total_hung_task is reset for each
> check_hung_uninterruptible_tasks() run.
>
> So some suggestions to align the documentation with the code's behavior
> below :)
>
True, I will change the comments as your suggestion, thanks
-Li
> On 2025/10/12 19:50, lirongqing wrote:
> > From: Li RongQing <lirongqing at 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 the system can recover, while others are
> > persistent and may accumulate progressively.
> >
> > This patch extends the 'hung_task_panic' sysctl to allow 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 still be fatal.
> >
> > The sysctl can be set to:
> > - 0: disabled (never panic)
> > - 1: original behavior (panic on first hung task)
> > - N: panic when N hung tasks are detected
> >
> > This maintains backward compatibility while providing more flexibility
> > for handling different hang scenarios.
> >
> > Signed-off-by: Li RongQing <lirongqing at baidu.com>
> > ---
> > Diff with v2: not add new sysctl, extend hung_task_panic
> >
> > Documentation/admin-guide/kernel-parameters.txt | 20
> +++++++++++++-------
> > Documentation/admin-guide/sysctl/kernel.rst | 3 ++-
> > arch/arm/configs/aspeed_g5_defconfig | 2 +-
> > kernel/configs/debug.config | 2 +-
> > kernel/hung_task.c | 16
> +++++++++++-----
> > lib/Kconfig.debug | 10
> ++++++----
> > tools/testing/selftests/wireguard/qemu/kernel.config | 2 +-
> > 7 files changed, 35 insertions(+), 20 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt
> > b/Documentation/admin-guide/kernel-parameters.txt
> > index a51ab46..7d9a8ee 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>
> > +
> > + Set this to the number of hung tasks that must be
> > + detected before triggering a kernel panic.
> > +
> > + 0: don't panic
> > + 1: panic immediately on first hung task
> > + N: panic after N hung tasks are detect
>
> The description should be more specific :)
>
> N: panic after N hung tasks are detected in a single scan
>
> Would it be better and cleaner?
>
> >
> > - 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..0a8dfab 100644
> > --- a/Documentation/admin-guide/sysctl/kernel.rst
> > +++ b/Documentation/admin-guide/sysctl/kernel.rst
> > @@ -397,7 +397,8 @@ 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 detected hung tasks reaches this value
>
> Hmm... that is also ambiguous ...
>
> +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.
> >
> > = =================================================
> > 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..3929ed9 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 +232,11 @@ 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 +305,7 @@ 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
> > +326,7 @@ 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 +395,7 @@ 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..077b9e4 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -1258,12 +1258,14 @@ 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.
> > + The number of hung tasks must be detected to trigger kernel panic.
> > +
> > + - 0: Don't trigger panic
> > + - N: Panic when N hung tasks are detected
>
> + - N: Panic when N hung tasks are detected in a single scan
>
> With these documentation changes, this patch would accurately describe its
> behavior, IMHO.
>
> >
> > 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
>
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