Executive brief
The Linux kernel's Btrfs filesystem can experience a service-blocking deadlock during data relocation operations on zoned storage devices. The relocation process becomes stuck waiting for disk space that it cannot free because it is itself responsible for freeing that space, causing storage operations to hang indefinitely. This fix introduces a specialized handling path to prevent the deadlock and restore normal operation.
Technical details
A circular dependency deadlock occurs in handle_reserve_tickets() when Btrfs performs data relocation on zoned filesystems. The relocation process requests a space reservation ticket that cannot be satisfied because the relocation itself must complete to free that space. The fix introduces a new flush state, BTRFS_RESERVE_FLUSH_ZONED_RELOCATION, that applies priority_reclaim_data_space() instead of the standard flushing path, avoiding re-entry into the relocation code. This new flush state is applied specifically when the inode belongs to a data relocation root on a zoned filesystem, as determined in btrfs_alloc_data_chunk_ondemand(). The patch modifies fs/btrfs/delalloc-space.c, fs/btrfs/space-info.c, and fs/btrfs/space-info.h.
Affected products
- Linux Linux kernel multiple versions affecting zoned Btrfs filesystems
Timeline
- 2026-08-15: disclosed
- 2026-06-09: patched: upstream commit 814c3b4ea357297c507158bceb07bcdc5fbe9808