linux-kernel - Re: [PATCH 2/3] hung_task: Add hung_task_sys_info sysctl to dump sys info on task-hung

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Message-ID: <aQwoukY-yU0bSX5f@U-2FWC9VHC-2323.local>
Date: Thu, 6 Nov 2025 12:48:58 +0800
From: Feng Tang <feng.tang@...ux.alibaba.com>
To: Lance Yang <lance.yang@...ux.dev>
Cc: paulmck@...nel.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lance Yang <ioworker0@...il.com>, Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH 2/3] hung_task: Add hung_task_sys_info sysctl to dump sys
 info on task-hung

On Thu, Nov 06, 2025 at 11:28:12AM +0800, Lance Yang wrote:
> 
> 
> On 2025/11/6 10:30, Feng Tang wrote:
> > When task-hung happens, developers may need different kinds of system
> > information (call-stacks, memory info, locks, etc.) to help debugging.
> > 
> > Add 'hung_task_sys_info' sysctl knob to take human readable string like
> > "tasks,mem,timers,locks,ftrace,...", and when task-hung happens, all
> > requested information will be dumped. (refer kernel/sys_info.c for more
> > details).
> > 
> > Meanwhile, the newly introduced sys_info() call is used to unify some
> > existing info-dumping knobs.
> 
> Thanks! Just one nit below.
> 
> > 
> > Signed-off-by: Feng Tang <feng.tang@...ux.alibaba.com>
> > ---
> >   Documentation/admin-guide/sysctl/kernel.rst |  5 +++
> >   kernel/hung_task.c                          | 39 +++++++++++++++------
> >   2 files changed, 33 insertions(+), 11 deletions(-)
> > 
> > diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> > index a397eeccaea7..45b4408dad31 100644
> > --- a/Documentation/admin-guide/sysctl/kernel.rst
> > +++ b/Documentation/admin-guide/sysctl/kernel.rst
> > @@ -422,6 +422,11 @@ the system boot.
> >   This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
> > +hung_task_sys_info
> > +==================
> > +A comma separated list of extra system information to be dumped when
> > +hung task is detected, for example, "tasks,mem,timers,locks,...".
> > +Refer 'panic_sys_info' section below for more details.
> >   hung_task_timeout_secs
> >   ======================
> > diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> > index 84b4b049faa5..102be5a8e75a 100644
> > --- a/kernel/hung_task.c
> > +++ b/kernel/hung_task.c
> > @@ -24,6 +24,7 @@
> >   #include <linux/sched/sysctl.h>
> >   #include <linux/hung_task.h>
> >   #include <linux/rwsem.h>
> > +#include <linux/sys_info.h>
> >   #include <trace/events/sched.h>
> > @@ -60,12 +61,23 @@ static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
> >   static int __read_mostly sysctl_hung_task_warnings = 10;
> >   static int __read_mostly did_panic;
> > -static bool hung_task_show_lock;
> >   static bool hung_task_call_panic;
> > -static bool hung_task_show_all_bt;
> >   static struct task_struct *watchdog_task;
> > +/*
> > + * A bitmask to control what kinds of system info to be printed when
> > + * a hung task is detected, it could be task, memory, lock etc. Refer
> > + * include/linux/sys_info.h for detailed bit definition.
> > + */
> > +static unsigned long hung_task_si_mask;
> > +
> > +/*
> > + * There are several sysctl knobs, and this serves as the runtime
> > + * effective sys_info knob
> > + */
> 
> Nit: let's make the comment for cur_si_mask even more explicit.
> +/*
> + * The effective sys_info mask for the current detection cycle. It
> + * aggregates the base hung_task_si_mask and any flags triggered
> + * by other conditions within this cycle. It is cleared after use.
> + */
> > +static unsigned long cur_si_mask;
> 
> That makes its lifecycle (aggregate, use, and clear) super obvious ;)

Yep. Thanks for the imporovement! Will take.

> With that, LGTM!
> 
> Reviewed-by: Lance Yang <lance.yang@...ux.dev>
Thanks!

- Feng