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x86/hotplug: Silence APIC only after all interrupts are migrated

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There is a race when taking a CPU offline. Current code looks like this:

native_cpu_disable()
{
	...
	apic_soft_disable();
	/*
	 * Any existing set bits for pending interrupt to
	 * this CPU are preserved and will be sent via IPI
	 * to another CPU by fixup_irqs().
	 */
	cpu_disable_common();
	{
		....
		/*
		 * Race window happens here. Once local APIC has been
		 * disabled any new interrupts from the device to
		 * the old CPU are lost
		 */
		fixup_irqs(); // Too late to capture anything in IRR.
		...
	}
}

The fix is to disable the APIC *after* cpu_disable_common().

Testing was done with a USB NIC that provided a source of frequent
interrupts. A script migrated interrupts to a specific CPU and
then took that CPU offline.

Fixes: 60dcaad5736f ("x86/hotplug: Silence APIC and NMI when CPU is dead")
Reported-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Tested-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Evan Green <evgreen@chromium.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/lkml/875zdarr4h.fsf@nanos.tec.linutronix.de/
Link: https://lore.kernel.org/r/1598501530-45821-1-git-send-email-ashok.raj@intel.com
This commit is contained in:
Ashok Raj 2020-08-26 21:12:10 -07:00 committed by Thomas Gleixner
parent d4f07268d0
commit 52d6b926aa
1 changed files with 20 additions and 6 deletions
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26
arch/x86/kernel/smpboot.c
View File

@ -1594,14 +1594,28 @@ int native_cpu_disable(void)
if (ret)
return ret;
/*
* Disable the local APIC. Otherwise IPI broadcasts will reach
* it. It still responds normally to INIT, NMI, SMI, and SIPI
* messages.
*/
apic_soft_disable();
cpu_disable_common();
/*
* Disable the local APIC. Otherwise IPI broadcasts will reach
* it. It still responds normally to INIT, NMI, SMI, and SIPI
* messages.
*
* Disabling the APIC must happen after cpu_disable_common()
* which invokes fixup_irqs().
*
* Disabling the APIC preserves already set bits in IRR, but
* an interrupt arriving after disabling the local APIC does not
* set the corresponding IRR bit.
*
* fixup_irqs() scans IRR for set bits so it can raise a not
* yet handled interrupt on the new destination CPU via an IPI
* but obviously it can't do so for IRR bits which are not set.
* IOW, interrupts arriving after disabling the local APIC will
* be lost.
*/
apic_soft_disable();
return 0;
}