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image: no hot-add rule for memory, which the kernel onlines itself #238

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Merged
aledbf merged 1 commit into from
Nov 12, 2026
Merged

image: no hot-add rule for memory, which the kernel onlines itself #238

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4 changes: 2 additions & 2 deletions image/mkosi.extra/usr/local/lib/spin-base/optimize-systemd.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -26,8 +26,8 @@ MASK_UNITS=(
# What masking cost was everything that needs a .device unit to exist.
#
# * serial-getty@ttyS0 carries BindsTo=dev-%i.device and could not start.
# * A hot-plugged CPU or memory block never produced an add event, so nothing could
# act on one — see 40-spin-hotadd.rules, which is the thing that acts on it.
# * A hot-plugged CPU never produced an add event, so nothing could act on one —
# see 40-spin-hotadd.rules, which is the thing that acts on it.

# Time sync - handled by host
systemd-timesyncd.service
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12 changes: 6 additions & 6 deletions image/mkosi.extra/usr/local/lib/spin-base/rootfs/etc/udev/rules.d/40-spin-hotadd.rules
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@@ -1,4 +1,4 @@
# Bring a hot-plugged CPU or memory block online, on this machine.
# Bring a hot-plugged CPU online, on this machine.
#
# The distribution ships a rule for exactly this, 40-vm-hotadd.rules, and it does nothing
# here: it opens by checking the DMI vendor for Microsoft Hyper-V or Xen and jumps past
Expand All @@ -15,9 +15,9 @@
# reach into the guest over RPC to online each core it just attached, which is a second
# mechanism doing what the guest's own event handling does, and one that stops being
# reachable the moment the guest's init hands over to something else.
#
# Memory has no rule: the kernel onlines each block itself, because memhp_default_state=online
# is always on the command line (machine/cmdline.go). The block's add uevent leaves before the
# kernel onlines it, so a rule here reads it offline, writes after the kernel has, and udevd
# logs EINVAL for every block a workspace grows by.
SUBSYSTEM=="cpu", ACTION=="add", DEVPATH=="/devices/system/cpu/cpu[0-9]*", TEST=="online", ATTR{online}!="1", ATTR{online}="1"

# Memory arrives through virtio-mem rather than as ACPI DIMMs, and the kernel command line
# already carries memhp_default_state=online — so this is the belt to that braces: a block
# the kernel did not online for itself still gets onlined here.
SUBSYSTEM=="memory", ACTION=="add", DEVPATH=="/devices/system/memory/memory[0-9]*", TEST=="state", ATTR{state}!="online", ATTR{state}="online"
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