Messages in this thread | | | Date | Wed, 19 Feb 2020 10:17:28 -0500 (EST) | From | Mathieu Desnoyers <> | Subject | Re: [RFC patch 14/19] bpf: Use migrate_disable() in hashtab code |
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----- On Feb 18, 2020, at 6:36 PM, Alexei Starovoitov alexei.starovoitov@gmail.com 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
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