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

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Message-ID: <20250219221141.09f9fe48@gandalf.local.home>
Date: Wed, 19 Feb 2025 22:11:41 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Waiman Long <llong@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Andrew
 Morton <akpm@...ux-foundation.org>, Boqun Feng <boqun.feng@...il.com>, Joel
 Granados <joel.granados@...nel.org>, Anna Schumaker
 <anna.schumaker@...cle.com>, Lance Yang <ioworker0@...il.com>, Kent
 Overstreet <kent.overstreet@...ux.dev>, Yongliang Gao
 <leonylgao@...cent.com>, Tomasz Figa <tfiga@...omium.org>, Sergey
 Senozhatsky <senozhatsky@...omium.org>, linux-kernel@...r.kernel.org, Linux
 Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH 1/2] hung_task: Show the blocker task if the task is
 hung on mutex

On Thu, 20 Feb 2025 11:40:36 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> Hmm, right.
> Since the blocked_on must be NULL before setting flag, if we can ensure
> the writing order so that blocked_flags is always updated before
> blocked_on, may it be safe?
> 
> Or, (this may introduce more memory overhead) don't use union but
> use different blocked_on_mutex, blocked_on_rwsem, etc. 
> 
> Another idea is to make the owner offset same, like introducing
> 
> struct common_lock {
> 	atomic_long_t owner;
> };
> 
> But the problem is that rt_mutex does not use atomic for storing
> the owner. (we can make it atomic using wrapper)

Either that, or add to the task_struct:

	struct mutex	*blocked_on_mutex;
	struct rwsem	*blocked_on_rwsem;
	struct rtlock	*blocked_on_rtlock;

And just have each type assign to its own type. Then you only need to look
at each one. But yeah, this adds even more bloat to task_struct.

  :-/

-- Steve