A deadlock occurs when Btrfs performs a reflink operation while a writeback flush is in progress on a filesystem mounted with the flushoncommit option. The bug appears when an inline extent is copied to a destination file at a non‑zero offset. The failure to update the destination file size that should have happened after the copy creates a circular wait between the transaction commit and the writeback work queue, causing the associated kworker to block indefinitely. The hang can exhaust kernel resources, potentially causing a denial of service for all tasks on the system. This deadlock exemplifies resource contention (CWE‑833) and improper synchronization.

Any system running a Linux kernel that contains the Btrfs filesystem and is using the flushoncommit mount option. No specific kernel release is listed in the data, so the vulnerability applies to all kernel versions before the commit that implements the described fix.

The CVSS score is 5.5, and the EPSS score is less than 1%. Based on the description, the attack vector is likely local or only achievable with elevated (root) privileges, as the exploit requires manipulating Btrfs reflink and transaction commit behavior. The risk is primarily a denial of service that manifests as a hung kworker and potentially system‑wide instability. No remote code execution or data exfiltration is implied. The vulnerability is a classic deadlock issue (CWE‑833).