Build a per-CPU detector coverage map before interpreting the absence of a lockup warning. Confirm the selected detector backend, runtime enablement, online CPUs and watchdog CPU mask. A latency-sensitive isolated CPU can be outside the default observation set even while the rest of the machine reports healthy progress. This guide uses upstream Linux v6.12. It…
Before stopping Linux in KGDB, identify everything that does not stop with the CPUs. A debugger can freeze software progress while a watchdog, DMA engine, peripheral or remote peer continues to advance. The resulting timeout, buffer change or reset may be caused by the debugging session rather than the original defect. This guide uses upstream…
Check return-probe instance capacity and missed-entry accounting before interpreting a missing return as a stuck function. A kretprobe needs state for each admitted in-flight invocation. If that state is exhausted, the observation can omit an invocation even though the function itself later returns normally. The baseline is upstream Linux v6.12 and the kernel kretprobe API….
Qualify the capture before using a missing trace event to explain a product failure. Save per-CPU loss statistics, enabled event filters, clock selection and reader behavior with the trace. A gap can mean the operation never happened, but it can also mean the recorder did not retain or deliver it. This guide uses upstream Linux…
Use irqsoff tracing to identify the beginning and end of an interrupt-disabled interval, then inspect the work performed inside it. A device missing its deadline does not by itself prove interrupts were masked. The diagnostic needs to connect a particular CPU, critical section and workload phase to the response requirement. The baseline is upstream Linux…
Start from the running kernel’s dynamic-debug catalog, select the few call sites that answer one question, and save their original flags before enabling them. A source file containing debug statements is not proof that those statements are available in the deployed image. A successful control-file write is not proof that the intended path executed. This…
Qualify netconsole as a complete sender-to-collector path before using its silence as evidence about a crash. Confirm the network device, destination addressing, receiver socket, capture format and loss accounting under an ordinary workload first. Then state which of those components can still operate during the failure being investigated. This guide uses upstream Linux v6.12. Netconsole…
Inject a failure at each relevant user-memory access and check the interface’s state-transition contract, not only whether it returns an error. A failed input copy must not leave unvalidated data published. A failed output copy needs a deliberate policy for work already committed, because returning an error cannot automatically undo a device operation. This article…
Use a controlled allocation-failure sweep to connect each observed failed allocation with the resources already acquired and the cleanup that follows. The pass condition is not merely an error return. The driver must preserve its contract, release partial state exactly once, and allow the next valid operation to succeed. This guide is pinned to upstream…
Choose Page Table Check when the hypothesis concerns an illegal userspace page mapping or a checked page-table flag combination, and when the target can run the required diagnostic kernel. It is most useful when a mapping mistake should be caught near the mapping update, before later application activity makes the failure difficult to attribute. The…