linux-kernel - Re: [BUG almost bisected] Splat in dequeue_rt

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Message-ID: <c83028db-55ad-45b3-a27a-842ed665a882@paulmck-laptop>
Date: Tue, 27 Aug 2024 10:33:13 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Valentin Schneider <vschneid@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
	sfr@...b.auug.org.au, linux-next@...r.kernel.org,
	kernel-team@...a.com
Subject: Re: [BUG almost bisected] Splat in dequeue_rt_stack() and build error

On Tue, Aug 27, 2024 at 05:41:52PM +0200, Valentin Schneider wrote:
> On 27/08/24 12:03, Valentin Schneider wrote:
> > On 26/08/24 09:31, Paul E. McKenney wrote:
> >> On Mon, Aug 26, 2024 at 01:44:35PM +0200, Valentin Schneider wrote:
> >>>
> >>> Woops...
> >>
> >> On the other hand, removing that dequeue_task() makes next-20240823
> >> pass light testing.
> >>
> >> I have to ask...
> >>
> >> Does it make sense for Valentin to rearrange those commits to fix
> >> the two build bugs and remove that dequeue_task(), all in the name of
> >> bisectability.  Or is there something subtle here so that only Peter
> >> can do this work, shoulder and all?
> >>
> >
> > I suppose at the very least another pair of eyes on this can't hurt, let me
> > get untangled from some other things first and I'll take a jab at it.
> 
> I've taken tip/sched/core and shuffled hunks around; I didn't re-order any
> commit. I've also taken out the dequeue from switched_from_fair() and put
> it at the very top of the branch which should hopefully help bisection.
> 
> The final delta between that branch and tip/sched/core is empty, so it
> really is just shuffling inbetween commits.
> 
> Please find the branch at:
> 
> https://gitlab.com/vschneid/linux.git -b mainline/sched/eevdf-complete-builderr
> 
> I'll go stare at the BUG itself now.

Thank you!

I have fired up tests on the "BROKEN?" commit.  If that fails, I will
try its predecessor, and if that fails, I wlll bisect from e28b5f8bda01
("sched/fair: Assert {set_next,put_prev}_entity() are properly balanced"),
which has stood up to heavy hammering in earlier testing.

							Thanx, Paul