[PATCH] kernel/hung_task: add option to ignore task

[Kassey Li]

By default, hung_task will iterate the tasklist and check
state in TASK_UNINTERRUPTIBLE with a given timeout value.

Some tasks may in this state as expected but reported by hung_task.
An example task and trace:

    [khungtaskd]Task SettingsProvide:2954 blocked for 90s is causing
    panic

     [<ffffffd6602f7470>] __switch_to+0x334
     [<ffffffd661c2f5b8>] __schedule+0x5e8
     [<ffffffd661c2f9f0>] schedule+0x9c
     [<ffffffd661c33da8>] schedule_hrtimeout_range_clock+0xd0
     [<ffffffd6605ef390>] do_epoll_wait+0x3c0
     [<ffffffd6605edd64>] __arm64_sys_epoll_pwait+0x48
     [<ffffffd660307494>] el0_svc_common+0xb4
     [<ffffffd6603073c4>] el0_svc_handler+0x6c
     [<ffffffd660084988>] el0_svc+0x8

Here we add an option for task_struct so it can be ignored.
Set this flag to default true, it do not break the origin desgin.

Suggested-by: Naman Jain <quic_namajain@xxxxxxxxxxx>
Signed-off-by: Kassey Li <quic_yingangl@xxxxxxxxxxx>
---
 include/linux/sched.h | 1 +
 kernel/fork.c         | 1 +
 kernel/hung_task.c    | 3 ++-
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e7b2f8a5c711..7c8596fea1f6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1071,6 +1071,7 @@ struct task_struct {
 #ifdef CONFIG_DETECT_HUNG_TASK
 	unsigned long			last_switch_count;
 	unsigned long			last_switch_time;
+	bool			hung_task_detect;
 #endif
 	/* Filesystem information: */
 	struct fs_struct		*fs;
diff --git a/kernel/fork.c b/kernel/fork.c
index 90c85b17bf69..5c461a37a26e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1552,6 +1552,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
 #ifdef CONFIG_DETECT_HUNG_TASK
 	tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
 	tsk->last_switch_time = 0;
+	tsk->hung_task_detect = 1;
 #endif
 
 	tsk->mm = NULL;
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index bb2354f73ded..74bf4cef857f 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -119,7 +119,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 	if (sysctl_hung_task_panic) {
 		console_verbose();
 		hung_task_show_lock = true;
-		hung_task_call_panic = true;
+		if (t->hung_task_detect)
+			hung_task_call_panic = true;
 	}
 
 	/*
-- 
2.17.1