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SubjectMSI interrupt for xhci still lost on 5.6-rc6 after cpu hotplug
Date
Hi

I can reproduce the lost MSI interrupt issue on 5.6-rc6 which includes
the "Plug non-maskable MSI affinity race" patch.

I can see this on a couple platforms, I'm running a script that first generates
a lot of usb traffic, and then in a busyloop sets irq affinity and turns off
and on cpus:

for i in 1 3 5 7; do
echo "1" > /sys/devices/system/cpu/cpu$i/online
done
echo "A" > "/proc/irq/*/smp_affinity"
echo "A" > "/proc/irq/*/smp_affinity"
echo "F" > "/proc/irq/*/smp_affinity"
for i in 1 3 5 7; do
echo "0" > /sys/devices/system/cpu/cpu$i/online
done

I added some very simple debugging but I don't really know what to look for.
xhci interrupts (122) just stop after a setting msi affinity, it survived many
similar msi_set_affinity() calls before this.

I'm not that familiar with the inner workings of this, but I'll be happy to
help out with adding debugging and testing patches.

Details:

cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7
0: 26 0 0 0 0 0 0 0 IO-APIC 2-edge timer
1: 0 0 0 0 0 7 0 0 IO-APIC 1-edge i8042
4: 0 4 59941 0 0 0 0 0 IO-APIC 4-edge ttyS0
8: 0 0 0 0 0 0 1 0 IO-APIC 8-edge rtc0
9: 0 40 8 0 0 0 0 0 IO-APIC 9-fasteoi acpi
16: 0 0 0 0 0 0 0 0 IO-APIC 16-fasteoi i801_smbus
120: 0 0 293 0 0 0 0 0 PCI-MSI 32768-edge i915
121: 728 0 0 58 0 0 0 0 PCI-MSI 520192-edge enp0s31f6
122: 63575 2271 0 1957 7262 0 0 0 PCI-MSI 327680-edge xhci_hcd
123: 0 0 0 0 0 0 0 0 PCI-MSI 514048-edge snd_hda_intel:card0
NMI: 0 0 0 0 0 0 0 0 Non-maskable interrupts

trace snippet:
<idle>-0 [001] d.h. 129.676900: xhci_irq: xhci irq
<idle>-0 [001] d.h. 129.677507: xhci_irq: xhci irq
<idle>-0 [001] d.h. 129.677556: xhci_irq: xhci irq
<idle>-0 [001] d.h. 129.677647: xhci_irq: xhci irq
<...>-14 [001] d..1 129.679802: msi_set_affinity: direct update msi 122, vector 33 -> 33, apicid: 2 -> 6
<idle>-0 [003] d.h. 129.682639: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.682769: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.682908: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.683552: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.683677: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.683819: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.689017: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.689140: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.689307: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.689984: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.690107: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.690278: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.695541: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.695674: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.695839: xhci_irq: xhci irq
<idle>-0 [003] d.H. 129.696667: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.696797: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.696973: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.702288: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.702380: xhci_irq: xhci irq
<idle>-0 [003] d.h. 129.702493: xhci_irq: xhci irq
migration/3-24 [003] d..1 129.703150: msi_set_affinity: direct update msi 122, vector 33 -> 33, apicid: 6 -> 0
kworker/0:0-5 [000] d.h. 131.328790: msi_set_affinity: direct update msi 121, vector 34 -> 34, apicid: 0 -> 0
kworker/0:0-5 [000] d.h. 133.312704: msi_set_affinity: direct update msi 121, vector 34 -> 34, apicid: 0 -> 0
kworker/0:0-5 [000] d.h. 135.360786: msi_set_affinity: direct update msi 121, vector 34 -> 34, apicid: 0 -> 0
<idle>-0 [000] d.h. 137.344694: msi_set_affinity: direct update msi 121, vector 34 -> 34, apicid: 0 -> 0
kworker/0:0-5 [000] d.h. 139.128679: msi_set_affinity: direct update msi 121, vector 34 -> 34, apicid: 0 -> 0
kworker/0:0-5 [000] d.h. 141.312686: msi_set_affinity: direct update msi 121, vector 34 -> 34, apicid: 0 -> 0
kworker/0:0-5 [000] d.h. 143.360703: msi_set_affinity: direct update msi 121, vector 34 -> 34, apicid: 0 -> 0
kworker/0:0-5 [000] d.h. 145.344791: msi_set_affinity: direct update msi 121, vector 34 -> 34, apicid: 0 -> 0


--- a/arch/x86/kernel/apic/msi.c
+++ b/arch/x86/kernel/apic/msi.c
@@ -92,6 +92,10 @@ msi_set_affinity(struct irq_data *irqd, const struct cpumask *mask, bool force)
cfg->vector == old_cfg.vector ||
old_cfg.vector == MANAGED_IRQ_SHUTDOWN_VECTOR ||
cfg->dest_apicid == old_cfg.dest_apicid) {
+ trace_printk("direct update msi %u, vector %u -> %u, apicid: %u -> %u\n",
+ irqd->irq,
+ old_cfg.vector, cfg->vector,
+ old_cfg.dest_apicid, cfg->dest_apicid);
irq_msi_update_msg(irqd, cfg);
return ret;
}
@@ -134,7 +138,10 @@ msi_set_affinity(struct irq_data *irqd, const struct cpumask *mask, bool force)
*/
if (IS_ERR_OR_NULL(this_cpu_read(vector_irq[cfg->vector])))
this_cpu_write(vector_irq[cfg->vector], VECTOR_RETRIGGERED);
-
+ trace_printk("twostep update msi, irq %u, vector %u -> %u, apicid: %u -> %u\n",
+ irqd->irq,
+ old_cfg.vector, cfg->vector,
+ old_cfg.dest_apicid, cfg->dest_apicid);
/* Redirect it to the new vector on the local CPU temporarily */
old_cfg.vector = cfg->vector;
irq_msi_update_msg(irqd, &old_cfg);
Thanks
-Mathias

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