linux-kernel - Re: [PATCH v5 1/3] hung_task: replace blocker

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Message-Id: <20250414143637.a1ae89d6b46c13f195e9210e@linux-foundation.org>
Date: Mon, 14 Apr 2025 14:36:37 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Lance Yang <ioworker0@...il.com>
Cc: will@...nel.org, peterz@...radead.org, mingo@...hat.com,
 longman@...hat.com, mhiramat@...nel.org, anna.schumaker@...cle.com,
 boqun.feng@...il.com, joel.granados@...nel.org, kent.overstreet@...ux.dev,
 leonylgao@...cent.com, linux-kernel@...r.kernel.org, rostedt@...dmis.org,
 senozhatsky@...omium.org, tfiga@...omium.org, amaindex@...look.com,
 jstultz@...gle.com, Mingzhe Yang <mingzhe.yang@...com>
Subject: Re: [PATCH v5 1/3] hung_task: replace blocker_mutex with encoded
 blocker

On Mon, 14 Apr 2025 22:59:43 +0800 Lance Yang <ioworker0@...il.com> wrote:

> This patch replaces 'struct mutex *blocker_mutex' with 'unsigned long
> blocker', as only one blocker is active at a time.
> 
> The blocker filed can store both the lock addrees and the lock type, with
> LSB used to encode the type as Masami suggested, making it easier to extend
> the feature to cover other types of locks.
> 
> Also, once the lock type is determined, we can directly extract the address
> and cast it to a lock pointer ;)
> 
> ...
>
>  static void debug_show_blocker(struct task_struct *task)
>  {
>  	struct task_struct *g, *t;
> -	unsigned long owner;
> -	struct mutex *lock;
> +	unsigned long owner, blocker;
>  
>  	RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "No rcu lock held");
>  
> -	lock = READ_ONCE(task->blocker_mutex);
> -	if (!lock)
> +	blocker = READ_ONCE(task->blocker);
> +	if (!blocker ||
> +	    hung_task_get_blocker_type(blocker) != BLOCKER_TYPE_MUTEX)
>  		return;
>  
> -	owner = mutex_get_owner(lock);
> +	owner = mutex_get_owner(
> +		(struct mutex *)hung_task_blocker_to_lock(blocker));

typecast is unneeded?