When mounting a btrfs file system on virtio-blk which supports native Zone Append there has been a WARN triggering in btrfs' space management code. Further looking into btrfs' zoned statistics uncovered the filesystem expecting the zones to be used, but the write pointers being 0: # cat /sys/fs/btrfs/8eabd2e7-3294-4f9e-9b58-7e64135c8bf4/zoned_stats active block-groups: 4 reclaimable: 0 unused: 0 need reclaim: false data relocation block-group: 1342177280 active zones: start: 1073741824, wp: 0 used: 0, reserved: 0, unusable: 0 start: 1342177280, wp: 0 used: 0, reserved: 0, unusable: 0 start: 1610612736, wp: 0 used: 16384, reserved: 0, unusable: 18446744073709535232 start: 1879048192, wp: 0 used: 131072, reserved: 0, unusable: 18446744073709420544 Looking at the blkzone report output for the zone in question (1610612736) the write pointer on the device moved, but the filesystem did not see a change on the write pointer: # blkzone report -c 1 -o 0x300000 /dev/vda start: 0x000300000, len 0x080000, cap 0x080000, wptr 0x000040 reset:0 non-seq:0, zcond: 2(oi) [type: 2(SEQ_WRITE_REQUIRED)] The zone write pointer is 0, because btrfs is using the cached version of blkdev_report_zones() and as virtio-blk is supporting native zone append, but blkdev_revalidate_zones() does not initialize the zone write plugs in this case. Not skipping the revalidate of sequential zones in blkdev_revalidate_zones() callchain fixes this issue. Signed-off-by: Johannes Thumshirn --- Note I'll also be sending a regression test to blktest for this issue. --- block/blk-zoned.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/blk-zoned.c b/block/blk-zoned.c index dcc295721c2c..831113667679 100644 --- a/block/blk-zoned.c +++ b/block/blk-zoned.c @@ -2096,7 +2096,7 @@ static int blk_revalidate_seq_zone(struct blk_zone *zone, unsigned int idx, * we have a zone write plug for such zone if the device has a zone * write plug hash table. */ - if (!queue_emulates_zone_append(disk->queue) || !disk->zone_wplugs_hash) + if (!disk->zone_wplugs_hash) return 0; wp_offset = disk_zone_wplug_sync_wp_offset(disk, zone); -- 2.52.0