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Use flock to avoid races with systemd-udevd that cause loop device partitions to briefly disappear. (LP: #2045586)

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Michael Hudson-Doyle 2024-02-19 06:54:39 +13:00
parent eb987eae64
commit 11b5162b14
2 changed files with 23 additions and 4 deletions
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8
debian/changelog vendored
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@ -1,3 +1,11 @@
livecd-rootfs (2.765.39) UNRELEASED; urgency=medium
[ dann frazier ]
* Use flock to avoid races with systemd-udevd that cause loop device
partitions to briefly disappear. (LP: #2045586)
-- Michael Hudson-Doyle <michael.hudson@ubuntu.com> Thu, 25 Jan 2024 07:45:58 +1300
livecd-rootfs (2.765.38) jammy; urgency=medium
* Add a largemem subarch for ubuntu-server that ships a 64k kernel variant

19
live-build/functions
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@ -67,16 +67,23 @@ mount_image() {
exit 1
fi
# As explained in excruciating detail in LP: #2045586, losetup
# races with udev in a way that can cause partition device files
# to briefly vanish. systemd docs say we can hold udev off by using
# flocks: https://systemd.io/BLOCK_DEVICE_LOCKING/
# `udevadm lock` isn't yet usable in Ubuntu, so we'll use flock for now
# Find the rootfs location
rootfs_dev_mapper="${loop_device}p${rootpart}"
if [ ! -b "${rootfs_dev_mapper}" ]; then
if flock -x ${loop_device} [ ! -b "${rootfs_dev_mapper}" ]; then
echo "${rootfs_dev_mapper} is not a block device";
exit 1
fi
# Add some information to the debug logs
echo "Mounted disk image ${backing_img} to ${rootfs_dev_mapper}"
blkid ${rootfs_dev_mapper}
flock -x ${loop_device} blkid ${rootfs_dev_mapper} \
|| echo "blkid failed; continuing"
return 0
}
@ -206,10 +213,14 @@ mount_disk_image() {
mount_partition "${rootfs_dev_mapper}" $mountpoint
local uefi_dev="${loop_device}p15"
if [ -b ${uefi_dev} -a -e $mountpoint/boot/efi ]; then
mount "${uefi_dev}" $mountpoint/boot/efi
if flock -x ${loop_device} \
[ -b ${uefi_dev} -a -e $mountpoint/boot/efi ]; then
flock -x ${loop_device} mount "${uefi_dev}" $mountpoint/boot/efi
fi
# Having one partition mounted should avoid udev-triggered partition
# rescans on that device, so we no longer need to flock.
# This is needed to allow for certain operations
# such as updating grub and installing software
cat > $mountpoint/usr/sbin/policy-rc.d << EOF