RTEMS | score: A time of day set dispatches inside the watchdog tickle (#5756)

[Sebastian Huber (@sebhub)]

Issue created by Sebastian Huber: https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5756



`_TOD_Set()` expires every realtime watchdog which the new time of day
reaches. It runs in the task which calls `rtems_clock_set()` or
`clock_settime()`. The only lock which that task holds is an API mutex,
so the task stays preemptible.

`_Watchdog_Do_tickle()` calls a service routine outside the lock of the
collection and with interrupts enabled. The service routine of a task
based timer sends an event to the timer server, and the send ends with a
thread dispatch. A timer server of a higher priority therefore runs
while the tickle phase is still in progress.

A task which runs in that window may delete an object which the service
routine of another watchdog of the same phase still reads. One processor
is enough for this order.

A service routine of the clock tick reaches no such window. It runs in
an interrupt, and a delete directive obtains the object allocator mutex,
which no interrupt handler may do.

Found in the review of the delete of a period. This description was
created with Claude Code assistance.

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5756
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