The deadlock in CVE-2026-74572 occurs because zoned_meta_io_lock is held across a blocking wait on transaction state in the tree-log block group path within check_bg_is_active(). The lock protects fs_info->active_meta_bg and fs_info->active_system_bg, but this code path doesn't actually touch those fields—it uses ctx->zoned_bg as its synchronization boundary instead. The lock was being held unnecessarily, and worse, across a call (btrfs_zone_finish_one_bg()) that can wait for transaction commit, creating a classic lock-induced deadlock. The fix drops the lock before the blocking operation and re-acquires after. What makes this analytically significant is that the sibling branch in check_bg_is_active() already implements this pattern correctly. That means the invariant was already understood and implemented in one code path but wasn't applied to another—likely when the tree-log path was added or refactored after the sibling pattern existed. The lock's scope was determined by call-site convention (held at function entry) rather than by what the lock actually protects at each point in the function. This is a structural pattern in kernel lock bugs: the fix is mechanically simple, but the existence of the bug reveals that lock scope decisions weren't intentional—they were inherited from the call site. For defenders, the implication is that zoned btrfs deployments with heavy metadata writeback and concurrent transaction commits are vulnerable, but the triggering conditions are narrow. The deeper lesson is that wherever zoned_meta_io_lock is held across a call that might indirectly wait on transaction state, the pattern needs review—and the invariant (what fields the lock actually protects) should be documented, because the code itself doesn't make that clear.
CVE-2026-74572
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIn 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisA detailed technical summary for this CVE is being prepared.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataThere is no version to upgrade to and no patch to apply. Every affected install stays exposed until the vendor ships a fix — or somebody else builds one.
Free. We build fixes in the order the community asks for them — and we’ll tell you the moment this one lands.
We develop and verify an original fix where the vendor hasn’t, from $4,900. Deployed to your staging first — never straight to production.
Scope it with usSee what else the community needs solved on the solutions-needed board.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-74572 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesThe deadlock in CVE-2026-74572 occurs because zoned_meta_io_lock is held across a blocking wait on transaction state in the tree-log block group path within check_bg_is_active(). The lock protects fs_info->active_meta_bg and fs_info->active_system_bg, but this code path doesn't actually touch those fields—it uses ctx->zoned_bg as its synchronization boundary instead. The lock was being held unnecessarily, and worse, across a call (btrfs_zone_finish_one_bg()) that can wait for transaction commit, creating a classic lock-induced deadlock. The fix drops the lock before the blocking operation and re-acquires after. What makes this analytically significant is that the sibling branch in check_bg_is_active() already implements this pattern correctly. That means the invariant was already understood and implemented in one code path but wasn't applied to another—likely when the tree-log path was added or refactored after the sibling pattern existed. The lock's scope was determined by call-site convention (held at function entry) rather than by what the lock actually protects at each point in the function. This is a structural pattern in kernel lock bugs: the fix is mechanically simple, but the existence of the bug reveals that lock scope decisions weren't intentional—they were inherited from the call site. For defenders, the implication is that zoned btrfs deployments with heavy metadata writeback and concurrent transaction commits are vulnerable, but the triggering conditions are narrow. The deeper lesson is that wherever zoned_meta_io_lock is held across a call that might indirectly wait on transaction state, the pattern needs review—and the invariant (what fields the lock actually protects) should be documented, because the code itself doesn't make that clear.
Practitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-74572 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data