kernel/thread: Cancel timeouts on k_thread_suspend(), make schedule point

When suspending a thread, cancel any pending timeouts which might wake
it up unexpectedly.  Also, make suspending the current thread
(specifically) a schedule point, as callers are clearly going to
expect that to be synchronous.

Also fix a documentation weirdness.  The phrasing in the earlier docs
for k_thread_suspend() was confusing: it could be interpreted as
either document the current (essentially buggy) behavior that threads
will "wake up" due to preexisting timeouts, OR to mean that thread
timeouts will continue to be tracked so that resuming a thread that
was sleeping will continue to sleep until the timeout (something that
has never been implemented: k_sleep() is implemented on top of
suspend).  Rewrite to document what we actually implement.

Fixes #20033

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
2 files changed