False For Equality | Atomic Test And Set Of Disk Block Returned

If a system is logging "Atomic Test and Set returned false" unexpectedly or excessively, the following issues should be investigated:

| Issue | Description | Review Recommendation | | :--- | :--- | :--- | | Lock Starvation | The thread holding the lock is taking too long (e.g., slow I/O, page fault). | Implement exponential backoff in the spin-loop or switch to a blocking semaphore if wait time exceeds a threshold. | | Deadlock | Thread A holds Lock X and waits for Lock Y; Thread B holds Y and returns false on X. | Review lock ordering policies. The false return is a symptom of a cyclical dependency. | | Forgotten Release | A thread acquired the lock but crashed or returned without releasing it. | The TS will return false indefinitely. Implement watchdog timers or recovery mechanisms to reset "stuck" locks. | | Priority Inversion | A high-priority thread spins on false returns, while the low-priority thread holding the lock is preempted and never runs. | Use priority inheritance protocols. | If a system is logging "Atomic Test and

Some storage engines store their replicated log as disk blocks. A leader might try to append a new log entry by performing a TAS on the next available log index block. If a follower (now acting as leader) has already written there, the TAS fails with this error. You may have computed the expected value incorrectly—for

Scenario: A node caches disk block values but fails to invalidate the cache after a write from another node.
Result: The node issues a test-and-set based on stale data, causing an unexpected failure.
Solution: Disable aggressive caching for shared block devices; use O_DIRECT or O_SYNC where appropriate. If a system is logging "Atomic Test and

For Pacemaker/Corosync:

pcs status
crm_verify -L -V
pcs cluster cib | grep reservation

You may have computed the expected value incorrectly—for example, using a stale version number. Recompute the expected value by re-reading the block immediately before TAS, not relying on cached data more than a few milliseconds old.