Re: [PATCH v4 1/2] hung_task: Show the blocker task if the task is hung on mutex

[Andrew Morton]

On Tue, 25 Feb 2025 16:02:34 +0900 "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> 
> The "hung_task" shows a long-time uninterruptible slept task, but most
> often, it's blocked on a mutex acquired by another task. Without
> dumping such a task, investigating the root cause of the hung task
> problem is very difficult.
> 
> This introduce task_struct::blocker_mutex to point the mutex lock
> which this task is waiting for. Since the mutex has "owner"
> information, we can find the owner task and dump it with hung tasks.
> 
> Note: the owner can be changed while dumping the owner task, so
> this is "likely" the owner of the mutex.
> 
> With this change, the hung task shows blocker task's info like below;

Seems useful.

> ...
>
> +static void debug_show_blocker(struct task_struct *task)
> +{
>
> ...
>
> +}
> +#else
> +#define debug_show_blocker(t)	do {} while (0)
> +#endif
> +

Nit. It's unpleasing to have one side a C function and the other a
macro.  Plus C functions are simply better - only use a macro if one
has to!

So,

--- a/kernel/hung_task.c~hung_task-show-the-blocker-task-if-the-task-is-hung-on-mutex-fix
+++ a/kernel/hung_task.c
@@ -125,7 +125,9 @@ static void debug_show_blocker(struct ta
 	}
 }
 #else
-#define debug_show_blocker(t)	do {} while (0)
+static inline void debug_show_blocker(struct task_struct *task)
+{
+}
 #endif
 
 static void check_hung_task(struct task_struct *t, unsigned long timeout)
_