On 17/03/2021 14:20, Johannes Thumshirn wrote: > On 17/03/2021 11:54, David Sterba wrote: >> On Wed, Mar 17, 2021 at 05:57:31PM +0900, Johannes Thumshirn wrote: >>> In btrfs_submit_direct() there's a WAN_ON_ONCE() that will trigger if >>> we're submitting a DIO write on a zoned filesystem but are not using >>> REQ_OP_ZONE_APPEND to submit the IO to the block device. >>> >>> This is a left over from a previous version where btrfs_dio_iomap_begin() >>> didn't use btrfs_use_zone_append() to check for sequential write only >>> zones. >> >> I can't identify the patch where this got changed. I've landed on >> 544d24f9de73 ("btrfs: zoned: enable zone append writing for direct IO") >> but that adds the btrfs_use_zone_append, the append flag and also the >> warning. >> > > It is an oversight from the development phase. In v11 (I think) I've added > 08f455593fff ("btrfs: zoned: cache if block group is on a sequential zone") > and forgot to remove the WARN_ON_ONCE() for 544d24f9de73 ("btrfs: zoned: > enable zone append writing for direct IO"). > > When developing auto relocation I got hit by the WARN as a block groups > where relocated to conventional zone and the dio code calls > btrfs_use_zone_append() introduced by 08f455593fff to check if it can use > zone append (a.k.a. if it's a sequential zone) or not and sets the appropriate > flags for iomap. > > I've never hit it in testing before, as I was relying on emulation to test > the conventional zones code but this one case wasn't hit, because on emulation > fs_info->max_zone_append_size is 0 and the WARN doesn't trigger either. >
I just realized that explanation should have gone into the commit message, do you want me to resend with a more elaborate commit message?