From: Peter Zijlstra <peterz@infradead.org>
To: Heiko Carstens <hca@linux.ibm.com>
Cc: Mikhail Zaslonko <zaslonko@linux.ibm.com>,
linux-next@vger.kernel.org, linux-s390@vger.kernel.org,
Ingo Molnar <mingo@kernel.org>,
Alexander Egorenkov <egorenar@linux.ibm.com>,
Thomas Gleixner <tglx@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: [linux-next][s390] Boot hang after merge c50f05bd3c4e (sched/hrtick)
Date: Thu, 5 Mar 2026 13:35:05 +0100 [thread overview]
Message-ID: <20260305123505.GA1395416@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260305121201.GB596554@noisy.programming.kicks-ass.net>
On Thu, Mar 05, 2026 at 01:12:01PM +0100, Peter Zijlstra wrote:
> > Any idea?
>
> Well, that all looks like timers are going missing. Which matches with
> Sven saying that disabling HRTIMER_REARM_DEFERRED makes it go again.
>
> I'm just not sure I can see why things would break between
> sched/hrtick (GOOD) and 1b8b1bb2a2fa (BAD).
>
> Looking at the diff (eg git diff d50da4b5915f..c50f05bd3c4e) show some
> idle time changes to s390 and various kernel/ changes, but nothing that
> stands out to me :/
That s390 idle time code..
0d785e2c324c ("s390/idle: Fix cpu idle exit cpu time accounting")
That moves this_cpu_add() from inside irq_enter_rcu() / irq_exit_rcu()
to outside of it.
Your this_cpu_add() as preempt_enable(), which does a preemption check.
Moving that before irq_enter_rcu() means it doesn't see HARDIRQ_OFFSET
in preempt_count(). As such, it might actually call into schedule() from
hardirq context.
Or am I missing something?
next prev parent reply other threads:[~2026-03-05 12:35 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-03 18:31 [linux-next][s390] Boot hang after merge c50f05bd3c4e (sched/hrtick) Mikhail Zaslonko
2026-03-04 16:13 ` Mikhail Zaslonko
2026-03-05 7:49 ` Heiko Carstens
2026-03-05 12:12 ` Peter Zijlstra
2026-03-05 12:35 ` Peter Zijlstra [this message]
2026-03-05 12:45 ` Peter Zijlstra
2026-03-05 13:07 ` Peter Zijlstra
2026-03-05 15:02 ` Heiko Carstens
2026-03-05 17:24 ` Mikhail Zaslonko
2026-03-05 19:48 ` Heiko Carstens
2026-03-06 8:41 ` Peter Zijlstra
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