linux-kernel - Re: [paulmck-rcu:dev.2023.11.08a] [EXP locktorture] 1254a620b4: WARNING:at_kernel/rcu/tree_stall.h:#rcu_stall_chain_notifier

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Message-ID: <4be82070-4cd5-4f31-8eb4-b38853fad865@paulmck-laptop>
Date:   Mon, 11 Dec 2023 20:26:12 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Oliver Sang <oliver.sang@...el.com>
Cc:     oe-lkp@...ts.linux.dev, lkp@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [paulmck-rcu:dev.2023.11.08a] [EXP locktorture] 1254a620b4:
 WARNING:at_kernel/rcu/tree_stall.h:#rcu_stall_chain_notifier_register

On Tue, Dec 12, 2023 at 10:06:36AM +0800, Oliver Sang wrote:
> hi, Paul,
> 
> On Mon, Dec 11, 2023 at 08:59:16AM -0800, Paul E. McKenney wrote:
> > On Thu, Dec 07, 2023 at 04:19:56PM +0800, kernel test robot wrote:
> > > 
> > > 
> > > Hello,
> > > 
> > > kernel test robot noticed "WARNING:at_kernel/rcu/tree_stall.h:#rcu_stall_chain_notifier_register" on:
> > > 
> > > commit: 1254a620b4a3832e65ac01bcef769b99e34515b2 ("EXP locktorture: Add RCU CPU stall-warning notifier stub")
> > > https://git.kernel.org/cgit/linux/kernel/git/paulmck/linux-rcu.git dev.2023.11.08a
> > 
> > Thank you for your testing efforts!
> > 
> > This one is expected behavior by explicit request from Linus Torvalds.
> > The concern is that people might use this hook without understanding
> > the risks of losing RCU CPU stall warnings.
> > 
> > One fix would be to never specify the rcupdate.rcu_cpu_stall_notifiers
> > kernel boot parameter.  Another would be to forgive this warning when
> > that boot parameter was specified.  Your choice!  ;-)
> 
> Thanks a lot for information!
> 
> this commit (1254a620b4) is a test for this warning, am I right?
> when this warning mechanism goes into upstream, do you want us still report
> for similar cases? or we could just ignore them? Thanks!

This 1254a620b4 ("EXP locktorture: Add RCU CPU stall-warning notifier
stub") commit is a debug-only use of this facility that will never go
upstream, as signified by the "EXP" at the beginning of the subject line.

Or is there some better way than "EXP" to mark commits that are not
intended for mainline?

							Thanx, Paul