linux-kernel - Re: [tip: timers/urgent] tick/nohz_full: Don't abuse smp_call_function_single() in tick_setup

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Message-ID: <ZmdXEDOdM8Oe4gl_@pavilion.home>
Date: Mon, 10 Jun 2024 21:42:08 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: linux-tip-commits@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org,
	x86@...nel.org
Subject: Re: [tip: timers/urgent] tick/nohz_full: Don't abuse
 smp_call_function_single() in tick_setup_device()

Le Mon, Jun 10, 2024 at 06:26:21PM -0000, tip-bot2 for Oleg Nesterov a écrit :
> The following commit has been merged into the timers/urgent branch of tip:
> 
> Commit-ID:     07c54cc5988f19c9642fd463c2dbdac7fc52f777
> Gitweb:        https://git.kernel.org/tip/07c54cc5988f19c9642fd463c2dbdac7fc52f777
> Author:        Oleg Nesterov <oleg@...hat.com>
> AuthorDate:    Tue, 28 May 2024 14:20:19 +02:00
> Committer:     Thomas Gleixner <tglx@...utronix.de>
> CommitterDate: Mon, 10 Jun 2024 20:18:13 +02:00
> 
> tick/nohz_full: Don't abuse smp_call_function_single() in tick_setup_device()
> 
> After the recent commit 5097cbcb38e6 ("sched/isolation: Prevent boot crash
> when the boot CPU is nohz_full") the kernel no longer crashes, but there is
> another problem.
> 
> In this case tick_setup_device() calls tick_take_do_timer_from_boot() to
> update tick_do_timer_cpu and this triggers the WARN_ON_ONCE(irqs_disabled)
> in smp_call_function_single().
> 
> Kill tick_take_do_timer_from_boot() and just use WRITE_ONCE(), the new
> comment explains why this is safe (thanks Thomas!).
> 
> Fixes: 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full")
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: stable@...r.kernel.org
> Link: https://lore.kernel.org/r/20240528122019.GA28794@redhat.com
> Link: https://lore.kernel.org/all/20240522151742.GA10400@redhat.com

I think we agreed on that version actually:

https://lore.kernel.org/all/20240603153557.GA8311@redhat.com/

Thanks.