On Wed, Oct 2, 2019 at 12:27 PM Anand Jain <anand.j...@oracle.com> wrote: > > > > I am looking for systemd part of the answers to understand what > is triggering a strange problem. Any help is appreciated. > > After mkfs.btrfs creates btrfs filesystem it scans to register the > device in btrfs.ko. > And we have 'btrfs dev scan --forget' command to undo the process of > register. > > But the problem is - immediately after 'btrfs dev scan --forget' the > systemd-udevd scans the device again, defeating the purpose of the > forget as show below (scanned-by). > > mkfs.btrfs -fq /dev/sdc && btrfs dev scan --forget /dev/sdc > > ------------------- > kernel: BTRFS: device fsid 8ea20bb2-888a-4b3b-9f4c-1db9117dc219 devid 1 > transid 5 /dev/sdc scanned-by mkfs.btrfs > kernel: BTRFS: device fsid 8ea20bb2-888a-4b3b-9f4c-1db9117dc219 devid 1 > transid 5 /dev/sdc scanned-by systemd-udevd > ------------------- > > And the problem does _not_ happen if there is a sleep of 3 secs after > the mkfs.btrfs, as below. > > mkfs.btrfs -fq /dev/sdc && sleep 3 && btrfs dev scan --forget /dev/sdc > > ------------------ > kernel: BTRFS: device fsid 601bd01a-5e6b-488a-b020-0e7556c83087 devid 1 > transid 5 /dev/sdc scanned-by mkfs.btrfs > ------------------ > > Any idea what happening from the systemd point of view? >
run udevadm monitor -ku in both cases and post results. My educated guess is that udev scan is in response to mkfs and you have unfortunate race condition here.
