fix: engine unmap uses write lock

[shuo-wu]

Which issue(s) this PR fixes:

Issue longhorn/longhorn#6406

What this PR does / why we need it:

Otherwise, there will be a race between unmap and write operations. See the ticket for details

Special notes for your reviewer:

Additional documentation or context

[coderabbitai]

Walkthrough

This pull request updates the UnmapAt method in the controller implementation by changing its locking mechanism. The method now acquires an exclusive write lock instead of a shared read lock, ensuring exclusive access to the controller’s state during unmapping operations. The corresponding unlocking call has been updated accordingly, while error logging and handling remain unchanged.

Changes

File	Change Summary
pkg/.../control.go	Updated UnmapAt method: switched from using RLock/RUnlock to Lock/Unlock for exclusive access during operations, with no change in logic.

Sequence Diagram(s)

sequenceDiagram
    participant C as Caller
    participant CT as Controller
    C->>CT: Invoke UnmapAt(length, off)
    CT->>CT: Acquire write lock (Lock)
    alt Valid conditions
        CT->>CT: Perform unmap operations
    else Invalid offset or state
        CT->>CT: Log error message
    end
    CT->>CT: Release write lock (Unlock)
    CT->>C: Return result/error

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• pkg/controller/control.go (3 hunks)

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🔇 Additional comments (1)

pkg/controller/control.go (1)

1118-1153: Approve lock mechanism change to prevent race condition.

The change from using a read lock (RLock) to a write lock (Lock) for the UnmapAt method is a crucial fix. This ensures exclusive access during unmap operations, preventing race conditions between unmap and write operations. All unlock calls have been consistently updated to match the new locking strategy.

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[shuo-wu]

@mergify backport v1.8.x

[shuo-wu]

@mergify backport v1.7.x

[mergify]

backport v1.8.x

✅ Backports have been created

• #1448 fix: engine unmap uses write lock (backport #1447) has been created for branch v1.8.x

[mergify]

backport v1.7.x

✅ Backports have been created

• #1449 fix: engine unmap uses write lock (backport #1447) has been created for branch v1.7.x

[PhanLe1010]

LGTM

[PhanLe1010]

Can we trigger a e2e CI run to see if this breaks anything?

[derekbit]

LGTM

[derekbit]

Can we trigger a e2e CI run to see if this breaks anything?

Running the regression test https://ci.longhorn.io/job/private/job/longhorn-tests-regression/