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partitioning: fix race condition on loop device allocation #6729

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Jun 22, 2024
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partitioning: fix race condition on loop device allocation #6729

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22 changes: 3 additions & 19 deletions lib/functions/image/partitioning.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -216,25 +216,9 @@ function prepare_partitions() {
flock -x $FD

declare -g LOOP
# replace losetup --find with own function and do 10 cycles
# losetup always return 1st free loop device and in parallel build,
# it often happens that same is found which resoults in:
# "failed to set up loop device: Device or resource busy"
# If we seek random way, chanches of allocating the same are significantly smaller.
FIND_LOOP_CYCLES=1
while : ; do
LOOP=$(find /dev/loop* | grep -Po "(\/dev\/loop\d|\/dev\/loop\d\d)$" | sort -R | head -1)
LOOP_COMPARE=$(losetup -l --noheadings --raw --output=NAME | grep $LOOP || true)
[[ -z $LOOP_COMPARE ]] && break
[[ $FIND_LOOP_CYCLES -gt 10 ]] && exit_with_error "Unable to find free loop device"
FIND_LOOP_CYCLES=$(( FIND_LOOP_CYCLES + 1 ))
done
display_alert "Allocated loop device" "LOOP=${LOOP} in cycle $FIND_LOOP_CYCLES"

CHECK_LOOP_FOR_SIZE="no" check_loop_device "$LOOP" # initially loop is zero sized, ignore it.

#--partscan is using to force the kernel for scaning partition table in preventing of partprobe errors
run_host_command_logged losetup --partscan "${LOOP}" "${SDCARD}".raw
#--partscan is using to force the kernel for scaning partition table in preventing of partprobe errors
LOOP=$(losetup --show --partscan --find "${SDCARD}".raw) || exit_with_error "Unable to find free loop device"
display_alert "Allocated loop device" "LOOP=${LOOP}"

# loop device was grabbed here, unlock
flock -u $FD
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