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Date: Thu, 5 Aug 2021 16:11:11 +0200
From: Michal Hocko <mhocko@...e.com>
To: chenguanyou <chenguanyou9338@...il.com>
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
keescook@...omium.org, lukas.bulwahn@...il.com, vbabka@...e.cz,
gpiccoli@...onical.com, chenguanyou <chenguanyou@...omi.com>
Subject: Re: [PATCH v2] hungtask: add filter kthread
On Thu 05-08-21 21:47:47, chenguanyou wrote:
> Some kernel threads are always in D state, when we enable hung_task,
> it will misjudge, we should skip these to narrow the scope.
>
> exp mediatek:
> root 435 435 2 0 0 mtk_lpm_monitor_thread 0 D LPM-0
> root 436 436 2 0 0 mtk_lpm_monitor_thread 0 D LPM-1
> root 437 437 2 0 0 mtk_lpm_monitor_thread 0 D LPM-2
> root 438 438 2 0 0 mtk_lpm_monitor_thread 0 D LPM-3
> root 439 439 2 0 0 mtk_lpm_monitor_thread 0 D LPM-4
> root 440 440 2 0 0 mtk_lpm_monitor_thread 0 D LPM-5
> root 441 441 2 0 0 mtk_lpm_monitor_thread 0 D LPM-6
> root 442 442 2 0 0 mtk_lpm_monitor_thread 0 D LPM-7
A similar approch has been proposed in the past (sorry I do not have
links handy) and always deemed a wrong way to approach the problem.
Either those kernel threads should be fixed to use less sleep or
annotate the sleep properly (TASK_IDLE).
> Signed-off-by: chenguanyou <chenguanyou@...omi.com>
> ---
> Documentation/admin-guide/sysctl/kernel.rst | 10 ++++++++++
> include/linux/sched/sysctl.h | 1 +
> kernel/hung_task.c | 8 ++++++++
> kernel/sysctl.c | 9 +++++++++
> lib/Kconfig.debug | 15 +++++++++++++++
> 5 files changed, 43 insertions(+)
>
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index 68b21395a743..3c7c74b26d95 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -405,6 +405,16 @@ This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
>
> -1: report an infinite number of warnings.
>
> +hung_task_filter_kthread
> +========================
> +
> +We should skip kthread when a hung task is detected.
> +This file shows up if ``CONFIG_DEFAULT_HUNG_TASK_FILTER_KTHREAD`` is enabled.
> +
> += =========================================================
> +0 Not skip detect kthread.
> +1 Skip detect kthread.
> += =========================================================
>
> hyperv_record_panic_msg
> =======================
> diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
> index db2c0f34aaaf..2b8b01b57559 100644
> --- a/include/linux/sched/sysctl.h
> +++ b/include/linux/sched/sysctl.h
> @@ -19,6 +19,7 @@ extern unsigned int sysctl_hung_task_panic;
> extern unsigned long sysctl_hung_task_timeout_secs;
> extern unsigned long sysctl_hung_task_check_interval_secs;
> extern int sysctl_hung_task_warnings;
> +extern unsigned int sysctl_hung_task_filter_kthread;
> int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
> void *buffer, size_t *lenp, loff_t *ppos);
> #else
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 396ebaebea3f..74ad75c2dde8 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -48,6 +48,11 @@ unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_
> */
> unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
>
> +/*
> + * Non-zero means no checking kthread
> + */
> +unsigned int __read_mostly sysctl_hung_task_filter_kthread = CONFIG_DEFAULT_HUNG_TASK_FILTER_KTHREAD;
> +
> int __read_mostly sysctl_hung_task_warnings = 10;
>
> static int __read_mostly did_panic;
> @@ -88,6 +93,9 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
> {
> unsigned long switch_count = t->nvcsw + t->nivcsw;
>
> + if (unlikely(sysctl_hung_task_filter_kthread && t->flags & PF_KTHREAD))
> + return;
> +
> /*
> * Ensure the task is not frozen.
> * Also, skip vfork and any other user process that freezer should skip.
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index d4a78e08f6d8..62067b9db486 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2513,6 +2513,15 @@ static struct ctl_table kern_table[] = {
> .proc_handler = proc_dointvec_minmax,
> .extra1 = &neg_one,
> },
> + {
> + .procname = "hung_task_filter_kthread",
> + .data = &sysctl_hung_task_filter_kthread,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = SYSCTL_ZERO,
> + .extra2 = SYSCTL_ONE,
> + },
> #endif
> #ifdef CONFIG_RT_MUTEXES
> {
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 678c13967580..d7063f955987 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1110,6 +1110,21 @@ config DEFAULT_HUNG_TASK_TIMEOUT
> A timeout of 0 disables the check. The default is two minutes.
> Keeping the default should be fine in most cases.
>
> +config DEFAULT_HUNG_TASK_FILTER_KTHREAD
> + int "Default filter kthread for hung task"
> + depends on DETECT_HUNG_TASK
> + range 0 1
> + default 0
> + help
> + This option controls filter kthread uses to determine when
> + a kernel task has become "state=TASK_UNINTERRUPTIBLE" and should be skipped.
> +
> + It can be adjusted at runtime via the kernel.hung_task_filter_kthread
> + sysctl or by writing a value to
> + /proc/sys/kernel/hung_task_filter_kthread.
> +
> + A filter of 1 disables the check.
> +
> config BOOTPARAM_HUNG_TASK_PANIC
> bool "Panic (Reboot) On Hung Tasks"
> depends on DETECT_HUNG_TASK
> --
> 2.17.1
--
Michal Hocko
SUSE Labs
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