ratelimit: Avoid jiffies=0 special case

ratelimit: Avoid jiffies=0 special case

The ___ratelimit() function special-cases the jiffies-counter value of zero
as "uninitialized".  This works well on 64-bit systems, where the jiffies
counter is not going to return to zero for more than half a billion years
on systems with HZ=1000, but similar 32-bit systems take less than 50 days
to wrap the jiffies counter.  And although the consequences of wrapping the
jiffies counter seem to be limited to minor confusion on the duration of
the rate-limiting interval that happens to end at time zero, it is almost
no work to avoid this confusion.

Therefore, introduce a RATELIMIT_INITIALIZED bit to the ratelimit_state
structure's ->flags field so that a ->begin value of zero is no longer
special.

Link: https://lore.kernel.org/all/fbe93a52-365e-47fe-93a4-44a44547d601@paulmck-laptop/
Link: https://lore.kernel.org/all/20250423115409.3425-1-spasswolf@web.de/
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>