----- On Feb 18, 2020, at 6:36 PM, Alexei Starovoitov alexei.starovoitov@xxxxxxxxx wrote: [...] > If I can use migrate_disable() without RT it will help my work on sleepable > BPF programs. I would only have to worry about rcu_read_lock() since > preempt_disable() is nicely addressed. Hi Alexei, You may want to consider using SRCU rather than RCU if you need to sleep while holding a RCU read-side lock. This is the synchronization approach I consider for adding the ability to take page faults when doing syscall tracing. Then you'll be able to replace preempt_disable() by combining SRCU and migrate_disable(): AFAIU eBPF currently uses preempt_disable() for two reasons: - Ensure the thread is not migrated, -> can be replaced by migrate_disable() in RT - Provide RCU existence guarantee through sched-RCU -> can be replaced by SRCU, which allows sleeping and taking page faults. I wonder if it would be acceptable to take a page fault while migration is disabled though ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
