netdev - Re: [PATCH V3 01/11] ARM: Disable FIQs (but not IRQs) on CPUs shutdown paths

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Date:   Mon, 17 Oct 2022 15:17:35 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, will@...nel.org,
        Mark Rutland <mark.rutland@....com>, arnd@...db.de,
        Catalin Marinas <catalin.marinas@....com>,
        kexec@...ts.infradead.org, pmladek@...e.com, bhe@...hat.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
        x86@...nel.org, kernel-dev@...lia.com, kernel@...ccoli.net,
        halves@...onical.com, fabiomirmar@...il.com,
        alejandro.j.jimenez@...cle.com, andriy.shevchenko@...ux.intel.com,
        bp@...en8.de, corbet@....net, d.hatayama@...fujitsu.com,
        dave.hansen@...ux.intel.com, dyoung@...hat.com,
        feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        xuqiang36@...wei.com
Subject: Re: [PATCH V3 01/11] ARM: Disable FIQs (but not IRQs) on CPUs
 shutdown paths

On Mon, Oct 17, 2022 at 11:00:46AM -0300, Guilherme G. Piccoli wrote:
> On 18/09/2022 10:58, Guilherme G. Piccoli wrote:
> > On 19/08/2022 19:17, Guilherme G. Piccoli wrote:
> >> Currently the regular CPU shutdown path for ARM disables IRQs/FIQs
> >> in the secondary CPUs - smp_send_stop() calls ipi_cpu_stop(), which
> >> is responsible for that. IRQs are architecturally masked when we
> >> take an interrupt, but FIQs are high priority than IRQs, hence they
> >> aren't masked. With that said, it makes sense to disable FIQs here,
> >> but there's no need for (re-)disabling IRQs.
> >>
> >> More than that: there is an alternative path for disabling CPUs,
> >> in the form of function crash_smp_send_stop(), which is used for
> >> kexec/panic path. This function relies on a SMP call that also
> >> triggers a busy-wait loop [at machine_crash_nonpanic_core()], but
> >> without disabling FIQs. This might lead to odd scenarios, like
> >> early interrupts in the boot of kexec'd kernel or even interrupts
> >> in secondary "disabled" CPUs while the main one still works in the
> >> panic path and assumes all secondary CPUs are (really!) off.
> >>
> >> So, let's disable FIQs in both paths and *not* disable IRQs a second
> >> time, since they are already masked in both paths by the architecture.
> >> This way, we keep both CPU quiesce paths consistent and safe.
> >>
> >> Cc: Marc Zyngier <maz@...nel.org>
> >> Cc: Michael Kelley <mikelley@...rosoft.com>
> >> Cc: Russell King <linux@...linux.org.uk>
> >> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
> >>
> 
> Monthly ping - let me know if there's something I should improve in
> order this fix is considered!

Patches don't get applied unless they end up in the patch system.
Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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