This killed a CQ run: https://luci-milo.appspot.com/buildbot/chromeos/sentry-paladin/3540

Parallel mksquashfs: Using 32 processors
Creating 4.0 filesystem on /mnt/host/source/src/build/images/sentry/R69-10860.0.0-rc1/rootfs/opt/google/containers/android/system.raw.img, block size 131072.
[=============================================================-] 9391/9391 100%Write failed because Bad file descriptor
FATAL ERROR:Failed to write to output filesystem

I think that this is the first time that I've seen this. Cause unknown and no CL in the batch could be related.