Timer race condition results in firmware crash

A use-after-free condition may occur due to scheduler contention between the EipTimer_Delete() function and an already-enqueued EipTimer_SlowExpiry() job. Under this race condition, a timer that has been deleted may still fire, leading to invalid memory access within the timer expiry handler and ultimately causing a firmware crash.

The issue occurs when EipTimer_Delete() removes a timer object while a corresponding EipTimer_SlowExpiry() job remains queued in the scheduler, under certain further conditions.

If the queued expiry job executes after the timer has been freed, under ceratin conditions, a use-after-free situation arises. This behavior has been observed for the TX timer during FwOpen/FwClose long-term testing of both, the netX90 and netX51/52 targets.

ETM tracing on netX51 revealed a coding error related to mutex handling in the timer module as the cause, which can lead to spurious executions of already deleted timers.