linux-kernel - Re: [PATCH v2] x86/hotplug: Silence APIC only after all irq's are migrated

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Message-ID: <595d331e-59f3-309c-a25d-f92c8aafb812@infradead.org>
Date:   Thu, 20 Aug 2020 20:16:29 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Ashok Raj <ashok.raj@...el.com>, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Sukumar Ghorai <sukumar.ghorai@...el.com>,
        Srikanth Nandamuri <srikanth.nandamuri@...el.com>,
        Evan Green <evgreen@...omium.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] x86/hotplug: Silence APIC only after all irq's are
 migrated

On 8/20/20 5:42 PM, Ashok Raj wrote:
> When offlining CPUs, fixup_irqs() migrates all interrupts away from the
> outgoing CPU to an online CPU. It's always possible the device sent an
> interrupt to the previous CPU destination. Pending interrupt bit in IRR in
> LAPIC identifies such interrupts. apic_soft_disable() will not capture any
> new interrupts in IRR. This causes interrupts from device to be lost during
> CPU offline. The issue was found when explicitly setting MSI affinity to a
> CPU and immediately offlining it. It was simple to recreate with a USB
> ethernet device and doing I/O to it while the CPU is offlined. Lost
> interrupts happen even when Interrupt Remapping is enabled.
> 
> Current code does apic_soft_disable() before migrating interrupts.
> 
> native_cpu_disable()
> {
> 	...
> 	apic_soft_disable();
> 	cpu_disable_common();
> 	  --> fixup_irqs(); // Too late to capture anything in IRR.
> }
> 
> Just flipping the above call sequence seems to hit the IRR checks
> and the lost interrupt is fixed for both legacy MSI and when
> interrupt remapping is enabled.
> 
> Fixes: 60dcaad5736f ("x86/hotplug: Silence APIC and NMI when CPU is dead")
> Link: https://lore.kernel.org/lkml/875zdarr4h.fsf@nanos.tec.linutronix.de/
> Reported-by: Evan Green <evgreen@...omium.org>
> Tested-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
> Tested-by: Evan Green <evgreen@...omium.org>
> Reviewed-by: Evan Green <evgreen@...omium.org>
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> ---
> v2:
> - Typos and fixes suggested by Randy Dunlap

Those all look good now.  Thanks for the update.

> To: linux-kernel@...r.kernel.org
> To: Thomas Gleixner <tglx@...utronix.de>
> Cc: Sukumar Ghorai <sukumar.ghorai@...el.com>
> Cc: Srikanth Nandamuri <srikanth.nandamuri@...el.com>
> Cc: Evan Green <evgreen@...omium.org>
> Cc: Mathias Nyman <mathias.nyman@...ux.intel.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: stable@...r.kernel.org
> ---
>  arch/x86/kernel/smpboot.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)


-- 
~Randy