bcachefs: Account for ioclock slop when throttling rebalance thread

This should fix an issue where the rebalance thread was spinning
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/rebalance.c

@@ -204,18 +204,22 @@ static int bch2_rebalance_thread(void *arg)
 			prev_run_time;
 
 		if (w.dev_most_full_percent < 20 && throttle > 0) {
-			r->state = REBALANCE_THROTTLED;
 			r->throttled_until_iotime = io_start +
 				div_u64(w.dev_most_full_capacity *
 					(20 - w.dev_most_full_percent),
 					50);
+
+			if (atomic_long_read(&clock->now) + clock->max_slop <
+			    r->throttled_until_iotime) {
 				r->throttled_until_cputime = start + throttle;
+				r->state = REBALANCE_THROTTLED;
 
 				bch2_kthread_io_clock_wait(clock,
 					r->throttled_until_iotime,
 					throttle);
 				continue;
 			}
+		}
 
 		/* minimum 1 mb/sec: */
 		r->pd.rate.rate =