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: <572e1211-79e2-4b8e-b36f-4eeca125427c@linux.dev>
Date: Thu, 6 Nov 2025 11:28:12 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: Feng Tang <feng.tang@...ux.alibaba.com>
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 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 ;)

With that, LGTM!

Reviewed-by: Lance Yang <lance.yang@...ux.dev>

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