On 10/10/23 01:34, Juri Lelli wrote:
Hi, On 09/10/23 15:15, Waiman Long wrote:The nr_deadline_tasks field in cpuset structure was introduced by commit 6c24849f5515 ("sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets"). Unlike nr_migrate_dl_tasks which is only modified under cpuset_mutex, nr_deadline_tasks can be updated in various contexts under different locks. As a result, data races may happen that cause incorrect value to be stored in nr_deadline_tasks leading to incorrectCould you please make an example of such data races?
Since update to cs->nr_deadline_tasks is not protected by a single lock, it is possible that multiple CPUs may try to modify it at the same time. It is possible that nr_deadline_tasks++ and nr_deadline_tasks-- can be done in a single instruction like in x86 and hence atomic. However, operation like "cs->nr_deadline_tasks += cs->nr_migrate_dl_tasks" is likely a RMW operation and so is subjected to racing. It is mostly theoretical, but probably not impossible.
Cheers, Longman
