From: Phil Auld <pauld@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Frederic Weisbecker <frederic@kernel.org>,
Nicholas Piggin <npiggin@gmail.com>,
Leonardo Bras <leobras@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
linux-kernel@vger.kernel.org, Junyao Zhao <junzhao@redhat.com>,
Chris von Recklinghausen <crecklin@redhat.com>
Subject: Re: [PATCH] sched/isolation: fix boot crash when maxcpus < first-housekeeping-cpu
Date: Thu, 18 Apr 2024 10:54:40 -0400 [thread overview]
Message-ID: <20240418145440.GD29188@lorien.usersys.redhat.com> (raw)
In-Reply-To: <20240413141746.GA10008@redhat.com>
On Sat, Apr 13, 2024 at 04:17:46PM +0200 Oleg Nesterov wrote:
> housekeeping_setup() checks cpumask_intersects(present, online) to ensure
> that the kernel will have at least one housekeeping CPU after smp_init(),
> but this doesn't work if the maxcpus= kernel parameter limits the number
> of processors available after bootup.
>
> For example, the kernel with "maxcpus=2 nohz_full=0-2" parameters crashes
> at boot time on my virtual machine with 4 CPUs.
>
> Change housekeeping_setup() to use cpumask_first_and() and check that the
> returned cpu number is valid and less than setup_max_cpus.
>
> 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 IIUC 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? I think
> 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.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Looks good to me. One less footgun.
Reviewed-by: Phil Auld <pauld@redhat.com>
> ---
> kernel/sched/isolation.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 2a262d3ecb3d..5891e715f00d 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -118,6 +118,7 @@ static void __init housekeeping_setup_type(enum hk_type type,
> static int __init housekeeping_setup(char *str, unsigned long flags)
> {
> cpumask_var_t non_housekeeping_mask, housekeeping_staging;
> + unsigned int first_cpu;
> int err = 0;
>
> if ((flags & HK_FLAG_TICK) && !(housekeeping.flags & HK_FLAG_TICK)) {
> @@ -138,7 +139,8 @@ static int __init housekeeping_setup(char *str, unsigned long flags)
> cpumask_andnot(housekeeping_staging,
> cpu_possible_mask, non_housekeeping_mask);
>
> - if (!cpumask_intersects(cpu_present_mask, housekeeping_staging)) {
> + first_cpu = cpumask_first_and(cpu_present_mask, housekeeping_staging);
> + if (first_cpu >= nr_cpu_ids || first_cpu >= setup_max_cpus) {
> __cpumask_set_cpu(smp_processor_id(), housekeeping_staging);
> __cpumask_clear_cpu(smp_processor_id(), non_housekeeping_mask);
> if (!housekeeping.flags) {
> @@ -147,6 +149,9 @@ static int __init housekeeping_setup(char *str, unsigned long flags)
> }
> }
>
> + if (cpumask_empty(non_housekeeping_mask))
> + goto free_housekeeping_staging;
> +
> if (!housekeeping.flags) {
> /* First setup call ("nohz_full=" or "isolcpus=") */
> enum hk_type type;
> --
> 2.25.1.362.g51ebf55
>
>
>
--
next prev parent reply other threads:[~2024-04-18 14:54 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 [this message]
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
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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