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: <20250219212303.6a49c011@gandalf.local.home>
Date: Wed, 19 Feb 2025 21:23:03 -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 11:07:07 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> On Wed, 19 Feb 2025 18:55:31 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Thu, 20 Feb 2025 07:56:39 +0900
> > Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
> >   
> > > > >> this field, we don't need to take lock, though taking the wait_lock may
> > > > >> still be needed to examine other information inside the mutex.    
> > > 
> > > Do we need to take it just for accessing owner, which is in an atomic?  
> > 
> > Updating the task_struct would be in the same location as the blocked_on is
> > anyway. I would make it into a wrapper function that is a nop when disabled.  
> 
> Should we make it depends on DEBUG_MUTEXES too? I think no. We can introduce
> a different kconfig and wrapper function which calls debug_mutex_*().

No it should only depend on HUNG_TASKS.

> 
> >   
> > >   
> > > > > But perhaps if we add a new config option for this feature, we could just
> > > > > add the lock that a task is blocked on before it goes to sleep and
> > > > > reference that instead. That would be easier than trying to play games
> > > > > getting the lock owner from the blocked_on field.    
> > > > 
> > > > Yes, it could be a new config option. This will be a useful feature that 
> > > > I believe most distros will turn it on. Or we may just include that in 
> > > > the core code without any option.    
> > > 
> > > Do we need another option? or just extend DETECT_HUNG_TASK?  
> > 
> > DETECT_HUNG_TASK is just that, for detecting hung tasks. This adds more
> > information to that, which increases the size of the task_struct not to
> > mention adds code in the mutex/rwsem handlers.
> > 
> > I would definitely make it a separate config that may depend on
> > DETECT_HUNG_TASK.  
> 
> OK, what about CONFIG_TASK_BLOCKER?

I'm fine with whatever color you would like the bikeshed to be ;-)

-- Steve