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

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Message-ID: <oiyb3a2qmf4hgqfyoztipno3d6j22ew77s43adt4rfd6kqhqvn@pqzvbsxgj2cq>
Date: Wed, 30 Jul 2025 18:56:33 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	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>, 
	Waiman Long <longman@...hat.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>, 
	Steven Rostedt <rostedt@...dmis.org>, Tomasz Figa <tfiga@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] hung_task: Show the blocker task if the task is
 hung on mutex

On (25/07/30 17:51), Masami Hiramatsu wrote:
[..]
> > Notice how each task is backtraced twice.  I wonder if it's worth it
> > to de-dup the backtraces.  E.g. in
> > 
> > 	task cat:115 is blocked on a mutex likely owned by task cat:114
> > 
> > if we know that cat:114 is also blocked on a lock, then we probably
> > can just say "is blocked on a mutex likely owned by task cat:114" and
> > continue iterating through tasks.  That "cat:114" will be backtraced
> > individually later, as it's also blocked on a lock, owned by another
> > task.
> > 
> > Does this make any sense?
> 
> Hrm, OK. So what about dump the blocker task only if that task is
> NOT blocked? (because if the task is blocked, it should be dumped
> afterwards (or already))

Yes, I think this is precisely what I tried to suggest.

I'm not saying that we should fix it, I just noticed that while looking
at some crash reports I found this
   "wait.. how is this possible... aah, same PID, so I saw that
   backtrace already"
a little inconvenient.