The Linux kernel vulnerability CVE-2026-45895 involves a livelock between quotactl_block() and freeze_super() during filesystem freeze operations. When the filesystem is frozen, quotactl_block() retries waiting for the thaw by acquiring and releasing locks and performing sb_start_write() - sb_end_write() calls. On kernels with disabled preemption, this retry loop spins without yielding the CPU, preventing the CPU from reaching an RCU quiescent state. Meanwhile, freeze_super() calls sb_wait_write(), which triggers synchronize_rcu() waiting for that quiescent state. The spin loop and RCU synchronization wait on each other indefinitely, causing a hang and 100% CPU usage. The issue is reproducible on multi-core systems when freeze and quota operations run on the same CPU. The fix involves inserting cond_resched() in the retry loop to allow RCU progress.

This vulnerability causes a hang of the freezer process and 100% CPU usage by the quota process, leading to denial of service on affected systems. There is no impact on confidentiality or integrity. The issue is triggered under specific kernel configurations (preemption disabled) and workload conditions involving filesystem freeze and quota toggling on the same CPU.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The described fix involves adding cond_resched() to the retry loop in quotactl_block() to allow RCU quiescent states and prevent livelock. Until an official patch is available, avoid running freeze and quota toggle operations concurrently on the same CPU with preemption disabled kernels.