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 13:19:46 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Waiman Long <llong@...hat.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Steven Rostedt <rostedt@...dmis.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>, 
	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>, 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 (25/02/19 22:49), Waiman Long wrote:
> On 2/19/25 9:45 PM, Sergey Senozhatsky wrote:
> > 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)
> 
> Bit lock doesn't have a owner field to track the owning task.

Right, so that's why I was thinking about keeping it outside in
a hashtable.  A list of owners plus a list of blocked_on per "lock",
be it a rwsem, or a mutex, or a bit.