mm/damon/core: avoid destroyed target reference from DAMOS quota

When the number of the monitoring targets in running contexts is reduced,
there may be DAMOS quotas referencing the targets that will be destroyed.

Applying the scheme action for such DAMOS scheme will be skipped forever
looking for the starting part of the region for the destroyed monitoring
target.

To fix this issue, when the monitoring target is destroyed, reset the
starting part for all DAMOS quotas that reference the target.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: da87878 ("mm/damon/sysfs: support online inputs update")
Signed-off-by: Akinobu Mita <[email protected]>
Reviewed-by: SeongJae Park <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: mita

mm/damon/core.c

@@ -1093,9 +1093,17 @@ static int damon_commit_targets(
 			if (err)
 				return err;
 		} else {
+			struct damos *s;
+
 			if (damon_target_has_pid(dst))
 				put_pid(dst_target->pid);
 			damon_destroy_target(dst_target);
+			damon_for_each_scheme(s, dst) {
+				if (s->quota.charge_target_from == dst_target) {
+					s->quota.charge_target_from = NULL;
+					s->quota.charge_addr_from = 0;
+				}
+			}
 		}
 	}