From: "Paul E. McKenney" <paulmck@kernel•org>
To: Valentin Schneider <vschneid@redhat•com>
Cc: Peter Zijlstra <peterz@infradead•org>,
linux-kernel@vger•kernel.org, sfr@canb•auug.org.au,
linux-next@vger•kernel.org, kernel-team@meta•com
Subject: Re: [BUG almost bisected] Splat in dequeue_rt_stack() and build error
Date: Tue, 27 Aug 2024 11:35:02 -0700 [thread overview]
Message-ID: <103b1710-39ca-40d0-947d-fdac32d6e6a0@paulmck-laptop> (raw)
In-Reply-To: <c83028db-55ad-45b3-a27a-842ed665a882@paulmck-laptop>
On Tue, Aug 27, 2024 at 10:33:13AM -0700, Paul E. McKenney wrote:
> 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.
And of 50 runs of TREE03 on the "BROKEN?" commit resulted in 32 failures.
Of these, 29 were the dequeue_rt_stack() failure. Two more were RCU
CPU stall warnings, and the last one was an oddball "kernel BUG at
kernel/sched/rt.c:1714" followed by an equally oddball "Oops: invalid
opcode: 0000 [#1] PREEMPT SMP PTI".
Just to be specific, this is commit:
df8fe34bfa36 ("BROKEN? sched/fair: Dequeue sched_delayed tasks when switching from fair")
This commit's predecessor is this commit:
2f888533d073 ("sched/eevdf: Propagate min_slice up the cgroup hierarchy")
This predecessor commit passes 50 runs of TREE03 with no failures.
So that addition of that dequeue_task() call to the switched_from_fair()
function is looking quite suspicious to me. ;-)
Thanx, Paul
next prev parent reply other threads:[~2024-08-27 18:35 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-21 21:57 [BUG almost bisected] Splat in dequeue_rt_stack() and build error Paul E. McKenney
2024-08-22 23:01 ` Paul E. McKenney
2024-08-23 7:47 ` Peter Zijlstra
2024-08-23 12:46 ` Paul E. McKenney
2024-08-23 21:51 ` Paul E. McKenney
2024-08-24 6:54 ` Peter Zijlstra
2024-08-24 15:26 ` Paul E. McKenney
2024-08-25 2:10 ` Paul E. McKenney
2024-08-25 19:36 ` Paul E. McKenney
2024-08-26 11:44 ` Valentin Schneider
2024-08-26 16:31 ` Paul E. McKenney
2024-08-27 10:03 ` Valentin Schneider
2024-08-27 15:41 ` Valentin Schneider
2024-08-27 17:33 ` Paul E. McKenney
2024-08-27 18:35 ` Paul E. McKenney [this message]
2024-08-27 20:30 ` Valentin Schneider
2024-08-27 20:36 ` Paul E. McKenney
2024-08-28 12:35 ` Valentin Schneider
2024-08-28 13:03 ` Paul E. McKenney
2024-08-28 13:40 ` Paul E. McKenney
2024-08-28 13:44 ` Chen Yu
2024-08-28 14:32 ` Valentin Schneider
2024-08-28 16:35 ` Paul E. McKenney
2024-08-28 18:17 ` Valentin Schneider
2024-08-28 18:39 ` Paul E. McKenney
2024-08-29 10:28 ` Paul E. McKenney
2024-08-29 13:50 ` Valentin Schneider
2024-08-29 14:13 ` Paul E. McKenney
2024-09-08 16:32 ` Paul E. McKenney
2024-09-13 14:08 ` Paul E. McKenney
2024-09-13 16:55 ` Valentin Schneider
2024-09-13 18:00 ` Paul E. McKenney
2024-09-30 19:09 ` Paul E. McKenney
2024-09-30 20:44 ` Valentin Schneider
2024-10-01 10:10 ` Paul E. McKenney
2024-10-01 12:52 ` Valentin Schneider
2024-10-01 16:47 ` Paul E. McKenney
2024-10-02 9:01 ` Tomas Glozar
2024-10-02 12:07 ` Paul E. McKenney
2024-10-10 11:24 ` Tomas Glozar
2024-10-10 15:01 ` Paul E. McKenney
2024-10-10 23:28 ` Paul E. McKenney
2024-10-14 18:55 ` Paul E. McKenney
2024-10-21 19:25 ` Paul E. McKenney
2024-11-14 18:16 ` Paul E. McKenney
2024-12-15 18:31 ` Paul E. McKenney
2024-12-16 14:38 ` Tomas Glozar
2024-12-16 19:36 ` Paul E. McKenney
2024-12-17 16:42 ` Paul E. McKenney
2024-10-22 6:33 ` Tomas Glozar
2024-10-03 8:40 ` Peter Zijlstra
2024-10-03 8:47 ` Peter Zijlstra
2024-10-03 9:27 ` Peter Zijlstra
2024-10-03 12:28 ` Peter Zijlstra
2024-10-03 12:45 ` Paul E. McKenney
2024-10-03 14:22 ` Peter Zijlstra
2024-10-03 16:04 ` Paul E. McKenney
2024-10-03 18:50 ` Peter Zijlstra
2024-10-03 19:12 ` Paul E. McKenney
2024-10-04 13:22 ` Paul E. McKenney
2024-10-04 13:35 ` Peter Zijlstra
2024-10-06 20:44 ` Paul E. McKenney
2024-10-07 9:34 ` Peter Zijlstra
2024-10-08 11:11 ` Peter Zijlstra
2024-10-08 16:24 ` Paul E. McKenney
2024-10-08 22:34 ` Paul E. McKenney
2024-10-03 12:44 ` Paul E. McKenney
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