From: Thomas Gleixner <tglx@linutronix.de>
To: Zhouyi Zhou <zhouzhouyi@gmail.com>,
fweisbec@gmail.com, mingo@kernel.org, dave@stgolabs.net,
paulmck@kernel.org, josh@joshtriplett.org, mpe@ellerman.id.au,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Cc: Zhouyi Zhou <zhouzhouyi@gmail.com>
Subject: Re: [PATCH linux-next][RFC]torture: avoid offline tick_do_timer_cpu
Date: Sat, 26 Nov 2022 18:05:05 +0100 [thread overview]
Message-ID: <87y1rxwsse.ffs@tglx> (raw)
In-Reply-To: <20221121035140.118651-1-zhouzhouyi@gmail.com>
On Mon, Nov 21 2022 at 11:51, Zhouyi Zhou wrote:
> During CPU-hotplug torture (CONFIG_NO_HZ_FULL=y), if we try to
> offline tick_do_timer_cpu, the operation will fail because in
> function tick_nohz_cpu_down:
> ```
> if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
> return -EBUSY;
> ```
> Above bug was first discovered in torture tests performed in PPC VM
How is this a bug?
> of Open Source Lab of Oregon State University, and reproducable in RISC-V
> and X86-64 (with additional kernel commandline cpu0_hotplug).
>
> In this patch, we avoid offline tick_do_timer_cpu by distribute
> the offlining cpu among remaining cpus.
Please read Documentation/process. Search for 'this patch'...
>
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
> ---
> include/linux/tick.h | 1 +
> kernel/time/tick-common.c | 1 +
> kernel/time/tick-internal.h | 1 -
> kernel/torture.c | 10 ++++++++++
> 4 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/tick.h b/include/linux/tick.h
> index bfd571f18cfd..23cc0b205853 100644
> --- a/include/linux/tick.h
> +++ b/include/linux/tick.h
> @@ -14,6 +14,7 @@
> #include <linux/rcupdate.h>
>
> #ifdef CONFIG_GENERIC_CLOCKEVENTS
> +extern int tick_do_timer_cpu __read_mostly;
> extern void __init tick_init(void);
> /* Should be core only, but ARM BL switcher requires it */
> extern void tick_suspend_local(void);
> diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
> index 46789356f856..87b9b9afa320 100644
> --- a/kernel/time/tick-common.c
> +++ b/kernel/time/tick-common.c
> @@ -48,6 +48,7 @@ ktime_t tick_next_period;
> * procedure also covers cpu hotplug.
> */
> int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
> +EXPORT_SYMBOL_GPL(tick_do_timer_cpu);
No. We are not exporting this just to make a bogus test case happy.
Fix the torture code to handle -EBUSY correctly.
Thanks,
tglx
next prev parent reply other threads:[~2022-11-26 17:05 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-21 3:51 [PATCH linux-next][RFC]torture: avoid offline tick_do_timer_cpu Zhouyi Zhou
2022-11-22 1:37 ` Paul E. McKenney
2022-11-23 2:23 ` Zhouyi Zhou
2022-11-23 18:49 ` Paul E. McKenney
2022-11-24 2:35 ` Zhouyi Zhou
2022-11-23 22:25 ` Frederic Weisbecker
2022-11-23 23:00 ` Paul E. McKenney
2022-11-23 22:36 ` Frederic Weisbecker
2022-11-24 2:18 ` Zhouyi Zhou
2022-11-26 17:05 ` Thomas Gleixner [this message]
2022-11-27 2:45 ` Zhouyi Zhou
2022-11-27 12:40 ` Thomas Gleixner
2022-11-27 17:53 ` Paul E. McKenney
2022-11-28 3:00 ` Zhouyi Zhou
2022-11-28 8:12 ` Thomas Gleixner
2022-11-28 15:16 ` Paul E. McKenney
2023-07-06 7:09 ` Christophe Leroy
2023-07-06 8:13 ` Zhouyi Zhou
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