linux-kernel - Re: [PATCH v3 04/15] arm: Don't use disable_nonboot

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Message-ID: <20200320134129.5udel4nplzgcfzwc@e107158-lin.cambridge.arm.com>
Date:   Fri, 20 Mar 2020 13:41:29 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 04/15] arm: Don't use disable_nonboot_cpus()

On 03/20/20 13:07, Russell King - ARM Linux admin wrote:
> On Fri, Mar 20, 2020 at 11:04:31AM +0000, Qais Yousef wrote:
> > On 02/23/20 19:29, Qais Yousef wrote:
> > > disable_nonboot_cpus() is not safe to use when doing machine_down(),
> > > because it relies on freeze_secondary_cpus() which in turn is
> > > a suspend/resume related freeze and could abort if the logic detects any
> > > pending activities that can prevent finishing the offlining process.
> > > 
> > > Beside disable_nonboot_cpus() is dependent on CONFIG_PM_SLEEP_SMP which
> > > is an othogonal config to rely on to ensure this function works
> > > correctly.
> > > 
> > > Use `reboot_cpu` variable instead of hardcoding 0 as the reboot cpu.
> 
> I think that should be a separate change - you have two separate
> changes in this patch:
> 
> 1. to switch to using the new helper.
> 2. to change the CPU that we potentially use for the final steps of
>    shutdown
> 
> These should be two seperate changes, so if (2) causes a regression
> it can be reverted independently of (1).

Okay will do.

Thanks

--
Qais Yousef

> 
> > > 
> > > Signed-off-by: Qais Yousef <qais.yousef@....com>
> > > CC: Russell King <linux@...linux.org.uk>
> > > CC: linux-arm-kernel@...ts.infradead.org
> > > CC: linux-kernel@...r.kernel.org
> > > ---
> > 
> > Hi Russel
> > 
> > Does the updated version look good to you now?
> > 
> > Thanks
> > 
> > --
> > Qais Yousef
> > 
> > >  arch/arm/kernel/reboot.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/arch/arm/kernel/reboot.c b/arch/arm/kernel/reboot.c
> > > index bb18ed0539f4..0ce388f15422 100644
> > > --- a/arch/arm/kernel/reboot.c
> > > +++ b/arch/arm/kernel/reboot.c
> > > @@ -88,11 +88,11 @@ void soft_restart(unsigned long addr)
> > >   * to execute e.g. a RAM-based pin loop is not sufficient. This allows the
> > >   * kexec'd kernel to use any and all RAM as it sees fit, without having to
> > >   * avoid any code or data used by any SW CPU pin loop. The CPU hotplug
> > > - * functionality embodied in disable_nonboot_cpus() to achieve this.
> > > + * functionality embodied in smp_shutdown_nonboot_cpus() to achieve this.
> > >   */
> > >  void machine_shutdown(void)
> > >  {
> > > -	disable_nonboot_cpus();
> > > +	smp_shutdown_nonboot_cpus(reboot_cpu);
> > >  }
> > >  
> > >  /*
> > > -- 
> > > 2.17.1
> > > 
> > 
> 
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up