Re: [RFC] btrfs: zoned: reset stale zones in unallocated device space

[Johannes Thumshirn <johannes.thumshirn@wdc.com>]

On 10/27/26 3:48 PM, Марк Коренберг wrote:
> Hi Johannes,
>
> I rebased your patch onto current master and found a few problems in
> review, so I reworked it. v2 is attached. Main issues:
>
> 1) Data loss during device replace: the replace target has no chunk
>     stripes until the replace finishes, so all data already copied to
>     it was reset, and the resumed replace never copies it again.
>     Trigger: start a replace, umount or remount,ro, then mount rw.
>     v2 skips the pass while a replace is ongoing.
>
> 2) Races: chunks can be allocated (data reloc bg, transaction kthread)
>     and removed (relocating repair after a read error) while the pass
>     runs, and the removal is not committed yet. v2 takes
>     reclaim_bgs_lock, commits, and holds chunk_mutex.
>
> 3) Used zones: v1 marked only the zone where each stripe starts. Today
>     stripes are exactly one zone long, but mount does not enforce that,
>     so a longer stripe would get its other zones reset. v2 checks
>     device->alloc_state instead, the allocator's own record of which
>     ranges belong to chunks, over the full stripe length. This also
>     drops the bitmap allocation that could fail the mount.
>
> 4) Zones that must not be reset: zones beyond total_bytes, read-only
>     devices, offline and read-only zones. v2 skips them.
>
> 5) v2 resets adjacent zones in one call and logs each reset range.
>
> The commit message also now says why the existing code does not help:
> btrfs_find_allocatable_zones() skips non-empty zones, so leaked zones
> are never reused. And the typo in your Signed-off-by is fixed.
>
> I used an AI assistant (Claude) for the review and for v2. v2 is build
> tested and checkpatch clean, not runtime tested yet.
>
> Please check that it still covers the case you hit, and tell me if you
> prefer to fold it into your patch or keep it as a fix on top.
Feel free to take over the patch, I have enough patches in flight atm 
that I need to get in, so one less on the plate is fine for me.