From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Phil Auld <pauld@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
x86@kernel.org
Subject: Re: [tip: sched/urgent] sched/isolation: Fix boot crash when maxcpus < first housekeeping CPU
Date: Sun, 28 Apr 2024 15:16:45 +0200 [thread overview]
Message-ID: <20240428131645.GA20436@redhat.com> (raw)
In-Reply-To: <Zi4FHsc51wNhdSW4@gmail.com>
On 04/28, Ingo Molnar wrote:
>
> * tip-bot2 for Oleg Nesterov <tip-bot2@linutronix.de> wrote:
>
> > Another corner case is "nohz_full=0" on a machine with a single CPU or with
> > the maxcpus=1 kernel argument. In this case non_housekeeping_mask is empty
> > and tick_nohz_full_setup() makes no sense. And indeed, the kernel hits the
> > WARN_ON(tick_nohz_full_running) in tick_sched_do_timer().
> >
> > And how should the kernel interpret the "nohz_full=" parameter? It should
> > be silently ignored, but currently cpulist_parse() happily returns the
> > empty cpumask and this leads to the same problem.
> >
> > Change housekeeping_setup() to check cpumask_empty(non_housekeeping_mask)
> > and do nothing in this case.
>
> So arguably the user meant NOHZ_FULL to be turned off - but it is de-facto
> already turned off by the fact that there's only a single CPU available,
> right?
Or the user passes the empty "nohz_full=" mask on a multi-CPU machine.
In both cases (before this patch) housekeeping_setup() calls
tick_nohz_full_setup(non_housekeeping_mask) which sets
tick_nohz_full_running = true even if tick_nohz_full_mask is empty.
This doesn't look right to me and triggers the "this should not happen"
warning in tick_sched_do_timer().
But let me repeat, I know nothing about nohz/etc.
Oleg.
next prev parent reply other threads:[~2024-04-28 13:18 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-30 1:00 [PATCH v2 1/1] wq: Avoid using isolated cpus' timers on queue_delayed_work Leonardo Bras
2024-01-30 1:22 ` Tejun Heo
2024-01-30 2:58 ` Leonardo Bras
2024-04-02 10:58 ` Oleg Nesterov
2024-04-03 19:12 ` Tejun Heo
2024-04-03 20:38 ` Oleg Nesterov
2024-04-05 14:04 ` Oleg Nesterov
2024-04-05 15:38 ` Tejun Heo
2024-04-05 22:03 ` Frederic Weisbecker
2024-04-05 21:52 ` Nohz_full on boot CPU is broken (was: Re: [PATCH v2 1/1] wq: Avoid using isolated cpus' timers on queue_delayed_work) Frederic Weisbecker
2024-04-07 13:09 ` Oleg Nesterov
2024-04-07 13:52 ` Oleg Nesterov
2024-04-09 12:05 ` Frederic Weisbecker
2024-04-09 12:04 ` Frederic Weisbecker
2024-04-09 13:07 ` Oleg Nesterov
2024-04-09 13:59 ` Frederic Weisbecker
2024-04-10 4:26 ` Nicholas Piggin
2024-04-10 13:55 ` Oleg Nesterov
2024-04-11 13:41 ` Oleg Nesterov
2024-04-11 14:39 ` [PATCH] sched/isolation: fix boot crash when the boot CPU is nohz_full Oleg Nesterov
2024-04-11 16:59 ` Oleg Nesterov
2024-04-13 14:17 ` [PATCH] sched/isolation: fix boot crash when maxcpus < first-housekeeping-cpu Oleg Nesterov
2024-04-18 14:54 ` Phil Auld
2024-04-18 15:40 ` Frederic Weisbecker
2024-04-24 20:05 ` [tip: sched/urgent] sched/isolation: Fix boot crash when maxcpus < first housekeeping CPU tip-bot2 for Oleg Nesterov
2024-04-28 8:13 ` Ingo Molnar
2024-04-28 13:16 ` Oleg Nesterov [this message]
2024-04-28 8:24 ` tip-bot2 for Oleg Nesterov
2024-04-15 21:37 ` [PATCH] sched/isolation: fix boot crash when the boot CPU is nohz_full Frederic Weisbecker
2024-04-18 14:50 ` Phil Auld
2024-04-22 18:50 ` Oleg Nesterov
2024-04-24 14:42 ` Phil Auld
2024-04-24 20:05 ` [tip: sched/urgent] sched/isolation: {revent " tip-bot2 for Oleg Nesterov
2024-04-24 20:41 ` Phil Auld
2024-04-28 8:14 ` Ingo Molnar
2024-04-29 11:50 ` Phil Auld
2024-04-28 8:24 ` [tip: sched/urgent] sched/isolation: Prevent " tip-bot2 for Oleg Nesterov
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