Atomic Test And Set Of Disk Block Returned False For Equality

Scenario: A process issues test-and-set without holding a prior persistent reservation.
Result: The storage target rejects the command.
Solution: Ensure the initiator has an active, registered reservation key before issuing atomic updates.

Scenario: One driver assumes 512-byte blocks; another uses 4096-byte blocks (4K native).
Result: Test-and-set on overlapping block regions fails repeatedly.
Solution: Standardize block size across all access paths (use blockdev --getbsz and --setbsz).

sg_persist -o -C /dev/sdX

Caution: Only clear reservations if you are certain no active node holds them. Scenario: A process issues test-and-set without holding a

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.

For Pacemaker/Corosync:

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

Some advanced storage controllers support atomic operations directly on hardware sectors. Caution: Only clear reservations if you are certain

The most poignant part of the prompt is the specific phrasing: "returned false for equality." In the context of a test-and-set, the "equality" in question is the match between the expected state (free/zero) and the actual state found.

If the instruction returns false, the equality has been rejected. The expected reality and the actual reality are out of sync. This is a fundamental rupture in the cognitive model of the software. The program operates under a linear assumption: "I checked the block; it appeared free; therefore, I will take it." The atomic test-and-set is the harsh correction to this assumption. It forces the software to confront the truth that looking is not touching, and seeing is not holding.

On a disk block, this rejection is even more profound. A disk is a medium of persistence; it is the long-term memory of the system. Unlike volatile RAM, which is fleeting, a disk block carries the weight of history. When a test-and-set fails on a disk block, it is often evidence of a "write-after-write" hazard or a stale read. The program held a cached image of the block as "free," but the persistent reality of the disk had already been altered by another agent. The "false for equality" is the disk asserting its autonomy. It refuses to be overwritten by a ghost—a process acting on outdated information. it appeared free

This failure acts as a boundary condition for the selfhood of a process. In concurrent programming, a process defines itself by its resources. "I am the process that owns Block X." When the test-and-set returns false, the process is stripped of that potential identity. It is told, "You are not the one. You do not own this. You are equal to the task, but the world does not match your view of it."

Engineers building high-performance LSM-trees or B-tree storage engines sometimes use block-level TAS to avoid finer-grained locks. This error indicates that a concurrent write or a partial block update corrupted the expected state.