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: <92c9b82b-2873-47af-a4ff-7e2f95f227d6@redhat.com>
Date: Wed, 19 Feb 2025 21:25:58 -0500
From: Waiman Long <llong@...hat.com>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
 Steven Rostedt <rostedt@...dmis.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 2/19/25 9:08 PM, Masami Hiramatsu (Google) wrote:
> On Wed, 19 Feb 2025 18:58:10 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
>
>> On Thu, 20 Feb 2025 08:09:08 +0900
>> Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
>>
>>> So something like this?
>>>
>>> unsigned int	block_flags;
>>> union {
>>> 	struct mutex	*mutex;
>>> 	struct rwsem	+rwsem;
>>> 	struct rtmutex	*rtmutex;
>>> } blocked_on;
>>>
>>> enum {
>>> 	BLOCKED_ON_MUTEX;
>>> 	BLOCKED_ON_RWSEM;
>>> 	BLOCKED_ON_RTMUTEX;
>>> 	BLOCKED_ON_IO;
>>> } block_reason;
>>>
>>> For the safety, we may anyway lock the task anyway, but that is the
>>> same as stacktrace.
>> Why not make it into a single entity?
>>
>> struct blocked_on {
>> 	unsigned int	flags;
>> 	union {
>> 		struct mutex	*mutex;
>> 		struct rwsem	*rwsem;
>> 		struct rtmutex	*rtmutex;
>> 	} blocked_on;
>> };
> Yes, and we also merge current mutex_waiter too.

I don't think we should merge mutex_waiter as it contains additional 
fields that are not useful to others. We don't want enlarge the size of 
task_struct unnecessarily.

Cheers,
Longman