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: <20250220-112040-neomutt-senozhatsky@chromium.org>
Date: Thu, 20 Feb 2025 11:45:30 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, 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 (25/02/20 08:09), Masami Hiramatsu 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;

I totally like this and always wanted to have something simlar,
something for all "sleepable" synchronization primitives, lightweight
enough (memory and CPU usage wise) to run on consumer devices.  I was
thinking of a rhashtable where each entry represents "sleepable"
primitive with a "owner" pointer and a list of "blocked on" tasks.
But I'm sure you'll have a better idea.

If I may add a couple of "wishes", can we also add:
- completions (so that things like wait_for_completion and
  synchronize srcu get covered)
- wait on bit (so that things like lock_buffer and so on get covered)