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Message-ID: <906dd11d-26db-4570-840a-e4797748c05c@molgen.mpg.de> Date: Thu, 16 Oct 2025 14:47:51 +0200 From: Paul Menzel <pmenzel@...gen.mpg.de> To: Li RongQing <lirongqing@...du.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Lance Yang <lance.yang@...ux.dev>, Masami Hiramatsu <mhiramat@...nel.org>, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-aspeed@...ts.ozlabs.org, wireguard@...ts.zx2c4.com, netdev@...r.kernel.org, linux-kselftest@...r.kernel.org, Andrew Jeffery <andrew@...econstruct.com.au>, Anshuman Khandual <anshuman.khandual@....com>, Arnd Bergmann <arnd@...db.de>, David Hildenbrand <david@...hat.com>, Florian Wesphal <fw@...len.de>, Jakub Kacinski <kuba@...nel.org>, "Jason A . Donenfeld" <jason@...c4.com>, Joel Granados <joel.granados@...nel.org>, Joel Stanley <joel@....id.au>, Jonathan Corbet <corbet@....net>, Kees Cook <kees@...nel.org>, Liam Howlett <liam.howlett@...cle.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Paul E . McKenney" <paulmck@...nel.org>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Petr Mladek <pmladek@...e.com>, Phil Auld <pauld@...hat.com>, Randy Dunlap <rdunlap@...radead.org>, Russell King <linux@...linux.org.uk>, Shuah Khan <shuah@...nel.org>, Simon Horman <horms@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Steven Rostedt <rostedt@...dmis.org> Subject: Re: [PATCH][v4] hung_task: Panic when there are more than N hung tasks at the same time 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@...du.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@...du.com> > Cc: Andrew Jeffery <andrew@...econstruct.com.au> > Cc: Anshuman Khandual <anshuman.khandual@....com> > Cc: Arnd Bergmann <arnd@...db.de> > Cc: David Hildenbrand <david@...hat.com> > Cc: Florian Wesphal <fw@...len.de> > Cc: Jakub Kacinski <kuba@...nel.org> > Cc: Jason A. Donenfeld <jason@...c4.com> > Cc: Joel Granados <joel.granados@...nel.org> > Cc: Joel Stanley <joel@....id.au> > Cc: Jonathan Corbet <corbet@....net> > Cc: Kees Cook <kees@...nel.org> > Cc: Lance Yang <lance.yang@...ux.dev> > Cc: Liam Howlett <liam.howlett@...cle.com> > Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com> > Cc: "Masami Hiramatsu (Google)" <mhiramat@...nel.org> > Cc: "Paul E . McKenney" <paulmck@...nel.org> > Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> > Cc: Petr Mladek <pmladek@...e.com> > Cc: Phil Auld <pauld@...hat.com> > Cc: Randy Dunlap <rdunlap@...radead.org> > Cc: Russell King <linux@...linux.org.uk> > Cc: Shuah Khan <shuah@...nel.org> > Cc: Simon Horman <horms@...nel.org> > Cc: Stanislav Fomichev <sdf@...ichev.me> > Cc: Steven Rostedt <rostedt@...dmis.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
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