On Aug 25, 2025 / 09:10, Bart Van Assche wrote:

Hi,

If I run blktests test zbd/009 on top of Jens' for-next branch
(commit 6763582c1263 ("Merge branch 'block-6.17' into for-next")) then
the test triggers a hang in btrfs_writepages(). The same test zbd/009
passes with older kernel versions (v6.16 and before). Other ZBD tests
pass with the same kernel. Could this indicate a BTRFS regression?

I hit the hang also, and identified the trigger commit 04147d8394e8 ("btrfs:
zoned: limit active zones to max_open_zones"), which is in the kernel tag
v6.17-rc3. Zoned btrfs requires max active zones limit of zoned block devices
to be at least 11 or greater. The commit applies the same requirement to
max_open_zones also. On the other hand, the default max_open_zones limit of
scsi_debug is 8. Hence the requirement is not met, and resulted in the hang.

On the blktests side, I will post a patch soon to set max_open_zones limit
larger than 11. I expect the limitation of zoned-btrfs to be checked by mkfs or
mount to avoid confusions.