Re: [RFC] sched: add sched_show_task() variant that accepts log level

[Tomasz Figa]

Hi Sergey,

On Mon, Mar 10, 2025 at 5:25 PM Sergey Senozhatsky
<senozhatsky@xxxxxxxxxxxx> wrote:
>
> Hi,
>
> A request for comments, not a formal patch.
>
> Is there any reason why hung-task watchdog prints error header
> with KERN_ERR log level while task's backtrace is printed with
> KERN_INFO?  Will it make sense to unify log levels and introduce
> sched_show_task() variant that accept log level param so that
> everything that hung-task watchdog prints becomes KERN_ERR?

Thanks a lot for looking into this.

Let me just add that I've been looking into ways to automatically
analyze kernel crash reports and I noticed that when I filter out
KERN_INFO and higher log levels, I end up losing useful information
for hung-task watchdog-kind of problems. This change would greatly
help in filtering out unnecessary noise from the logs.

By the way, if having it as KERN_INFO by default would still be
desirable, I suppose we could add a KConfig option to set the desired
log level?

Best regards,
Tomasz

>
> Something like this:
>
> ---
>  include/linux/sched/debug.h |  1 +
>  kernel/hung_task.c          |  4 ++--
>  kernel/sched/core.c         | 19 +++++++++++++------
>  3 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/sched/debug.h b/include/linux/sched/debug.h
> index b5035afa2396..8e46854d16fc 100644
> --- a/include/linux/sched/debug.h
> +++ b/include/linux/sched/debug.h
> @@ -34,6 +34,7 @@ extern void show_stack(struct task_struct *task, unsigned long *sp,
>                        const char *loglvl);
>
>  extern void sched_show_task(struct task_struct *p);
> +extern void sched_show_task_log_lvl(struct task_struct *p, const char *lvl);
>
>  #ifdef CONFIG_SCHED_DEBUG
>  struct seq_file;
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index ccd7217fcec1..23dec32a05f3 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -119,7 +119,7 @@ static void debug_show_blocker(struct task_struct *task)
>                 if ((unsigned long)t == owner) {
>                         pr_err("INFO: task %s:%d is blocked on a mutex likely owned by task %s:%d.\n",
>                                 task->comm, task->pid, t->comm, t->pid);
> -                       sched_show_task(t);
> +                       sched_show_task_log_lvl(t, KERN_ERR);
>                         return;
>                 }
>         }
> @@ -186,7 +186,7 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
>                         pr_err("      Blocked by coredump.\n");
>                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
>                         " disables this message.\n");
> -               sched_show_task(t);
> +               sched_show_task_log_lvl(t, KERN_ERR);
>                 debug_show_blocker(t);
>                 hung_task_show_lock = true;
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 00ea6f31973c..b6a5a41fbbfc 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7687,7 +7687,7 @@ void __sched io_schedule(void)
>  }
>  EXPORT_SYMBOL(io_schedule);
>
> -void sched_show_task(struct task_struct *p)
> +void sched_show_task_log_lvl(struct task_struct *p, const char *lvl)
>  {
>         unsigned long free;
>         int ppid;
> @@ -7695,7 +7695,8 @@ void sched_show_task(struct task_struct *p)
>         if (!try_get_task_stack(p))
>                 return;
>
> -       pr_info("task:%-15.15s state:%c", p->comm, task_state_to_char(p));
> +       printk("%stask:%-15.15s state:%c", lvl,
> +              p->comm, task_state_to_char(p));
>
>         if (task_is_running(p))
>                 pr_cont("  running task    ");
> @@ -7709,12 +7710,18 @@ void sched_show_task(struct task_struct *p)
>                 free, task_pid_nr(p), task_tgid_nr(p),
>                 ppid, p->flags, read_task_thread_flags(p));
>
> -       print_worker_info(KERN_INFO, p);
> -       print_stop_info(KERN_INFO, p);
> -       print_scx_info(KERN_INFO, p);
> -       show_stack(p, NULL, KERN_INFO);
> +       print_worker_info(lvl, p);
> +       print_stop_info(lvl, p);
> +       print_scx_info(lvl, p);
> +       show_stack(p, NULL, lvl);
>         put_task_stack(p);
>  }
> +EXPORT_SYMBOL_GPL(sched_show_task_log_lvl);
> +
> +void sched_show_task(struct task_struct *p)
> +{
> +       sched_show_task_log_lvl(p, KERN_INFO);
> +}
>  EXPORT_SYMBOL_GPL(sched_show_task);
>
>  static inline bool
> --
> 2.49.0.rc0.332.g42c0ae87b1-goog
>