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Message-ID: <aRVI4EcFu83Lx3TE@U-2FWC9VHC-2323.local>
Date: Thu, 13 Nov 2025 10:56:32 +0800
From: Feng Tang <feng.tang@...ux.alibaba.com>
To: Petr Mladek <pmladek@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Lance Yang <ioworker0@...il.com>, paulmck@...nel.org,
Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] hung_task: Add hung_task_sys_info sysctl to dump sys
info on task-hung
On Wed, Nov 12, 2025 at 03:44:09PM +0100, Petr Mladek wrote:
> On Wed 2025-11-12 19:25:27, Feng Tang wrote:
> > On Mon, Nov 10, 2025 at 06:55:57PM +0100, Petr Mladek wrote:
> > > On Thu 2025-11-06 10:30:31, Feng Tang wrote:
> > [...]
> > > @@ -315,8 +295,10 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> > > {
> > > int max_count = sysctl_hung_task_check_count;
> > > unsigned long last_break = jiffies;
> > > + unsigned long total_hung_task;
> > > struct task_struct *g, *t;
> > > unsigned long prev_detect_count = sysctl_hung_task_detect_count;
> > > + unsigned long si_mask;
> > >
> > > /*
> > > * If the system crashed already then all bets are off,
> > > @@ -325,6 +307,14 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> > > if (test_taint(TAINT_DIE) || did_panic)
> > > return;
> > >
> > > + si_mask = hung_task_si_mask;
> > > + if (sysctl_hung_task_warnings || hung_task_call_panic) {
> > > + si_mask |= SYS_INFO_LOCKS;
> > > +
> > > + if (sysctl_hung_task_all_cpu_backtrace)
> > > + si_mask |= SYS_INFO_ALL_BT;
> > > + }
> >
> > This probably needs to be moved to after the loop check of
> > check_hung_task().
>
> I did it on purpose because "sysctl_hung_task_warnings" might get
> decremented down to "0" in the loop below. But IMHO, we need to print
> the information if it was non-zero at the beginning.
>
> It might be worth to add a comment why it has to be done
> before the cycle.
I see your point. Yes, that could happen and should be handled.
My concern was:
1. 'hung_task_call_panic' is actually set in the following loop of
checking, and should be checked after the loop
2. when 'sysctl_hung_task_warnings' is not 0 (likely), the
si_mask |= SYS_INFO_LOCKS
will make it always call sys_info() will non-zero value, while the
'hung_task_si_mask' could be pre-set. I just run a simple hung task
test and can confirm this.
So I made some small changes based on your patches, please help to
review.
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 5f0275b2c742..5b3a7785d3a2 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -71,12 +71,6 @@ static struct task_struct *watchdog_task;
*/
static unsigned long hung_task_si_mask;
-/*
- * There are several sysctl knobs, and this serves as the runtime
- * effective sys_info knob
- */
-static unsigned long cur_si_mask;
-
#ifdef CONFIG_SMP
/*
* Should we dump all CPUs backtraces in a hung task event?
@@ -229,11 +223,8 @@ 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,
- unsigned long prev_detect_count)
+static void check_hung_task(struct task_struct *t, unsigned long timeout)
{
- unsigned long total_hung_task;
-
if (!task_is_hung(t, timeout))
return;
@@ -243,21 +234,13 @@ 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);
- cur_si_mask = hung_task_si_mask;
- if (sysctl_hung_task_panic && total_hung_task >= sysctl_hung_task_panic) {
- console_verbose();
- cur_si_mask |= SYS_INFO_LOCKS;
- hung_task_call_panic = true;
- }
-
/*
* Ok, the task did not get scheduled for more than 2 minutes,
* complain:
*/
- if (sysctl_hung_task_warnings || hung_task_call_panic) {
+ if (sysctl_hung_task_warnings) {
if (sysctl_hung_task_warnings > 0)
sysctl_hung_task_warnings--;
pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
@@ -272,10 +255,7 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout,
" disables this message.\n");
sched_show_task(t);
debug_show_blocker(t, timeout);
- cur_si_mask |= SYS_INFO_LOCKS;
- if (sysctl_hung_task_all_cpu_backtrace)
- cur_si_mask |= SYS_INFO_ALL_BT;
if (!sysctl_hung_task_warnings)
pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
}
@@ -315,8 +295,11 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
{
int max_count = sysctl_hung_task_check_count;
unsigned long last_break = jiffies;
+ unsigned long total_hung_task;
struct task_struct *g, *t;
unsigned long prev_detect_count = sysctl_hung_task_detect_count;
+ int need_warning = sysctl_hung_task_warnings;
+ unsigned long si_mask = hung_task_si_mask;
/*
* If the system crashed already then all bets are off,
@@ -325,6 +308,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
if (test_taint(TAINT_DIE) || did_panic)
return;
+
rcu_read_lock();
for_each_process_thread(g, t) {
@@ -336,16 +320,29 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
last_break = jiffies;
}
- check_hung_task(t, timeout, prev_detect_count);
+ check_hung_task(t, timeout);
}
unlock:
rcu_read_unlock();
- if (unlikely(cur_si_mask)) {
- sys_info(cur_si_mask);
- cur_si_mask = 0;
+ total_hung_task = sysctl_hung_task_detect_count - prev_detect_count;
+ if (!total_hung_task)
+ return;
+
+ if (sysctl_hung_task_panic && total_hung_task >= sysctl_hung_task_panic) {
+ console_verbose();
+ hung_task_call_panic = true;
}
+ if (need_warning || hung_task_call_panic) {
+ si_mask |= SYS_INFO_LOCKS;
+
+ if (sysctl_hung_task_all_cpu_backtrace)
+ si_mask |= SYS_INFO_ALL_BT;
+ }
+
+ sys_info(si_mask);
+
if (hung_task_call_panic)
panic("hung_task: blocked tasks");
}
Thanks,
Feng
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