lib/logstorage: prevent delete tasks from merging replaced parts

[func25]

Deletion searches for matching parts outside partsLock. But there is a race window that a part can be merged and replaced after the search finishes but right before the deletion task claims it, this causes a panic as we are trying to merge (of deletion) a suppose-to-delete part.

// check matching part
if !pw.p.hasMatchingRows(pso, stopCh) {
	continue
}

// --- RACE window

// claim
ddb.partsLock.Lock()
if !pw.isInMerge {
	pw.isInMerge = true
	pwsToMerge = append(pwsToMerge, pw)
} else {
	needRepeat = true
}
ddb.partsLock.Unlock()

Move mustDrop marking under partsLock and check it before the deletion task claims a part, so replaced parts are retried instead.

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}