[PATCH v2] hungtask: add filter kthread

[chenguanyou]

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

Signed-off-by: chenguanyou <chenguanyou@xxxxxxxxxx>
---
 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