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From: Martin Wilck via lttng-dev <lttng-dev@lists.lttng.org>
To: lttng-dev@lists.lttng.org
Subject: [lttng-dev] User-space RCU: call rcu_barrier() before dissociating helper thread?
Date: Thu, 29 Apr 2021 15:49:43 +0200	[thread overview]
Message-ID: <ebac01302ecae6cc2dd0ace8fcfffa6ab593e0fe.camel@suse.com> (raw)

In multipath-tools, we are using a custom RCU helper thread, which is cleaned out
on exit:

https://github.com/opensvc/multipath-tools/blob/23a01fa679481ff1144139222fbd2c4c863b78f8/multipathd/main.c#L3058

I put a call to rcu_barrier() there in order to make sure all callbacks had finished
before detaching the helper thread.

Now we got a report that rcu_barrier() isn't available before user-space RCU 0.8 
(https://github.com/opensvc/multipath-tools/issues/5) (and RHEL7 / Centos7 
still has 0.7.16).

Question: was it over-cautious or otherwise wrong to call rcu_barrier() before
set_thread_call_rcu_data(NULL)? Can we maybe just skip this call? If no, what
would be the recommended way for liburcu < 0.8 to dissociate a helper thread?

(Note: I'm not currently subscribed to lttng-dev).

Regards and thanks,
Martin



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             reply	other threads:[~2021-04-29 14:09 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-29 13:49 Martin Wilck via lttng-dev [this message]
2021-04-30 18:41 ` [lttng-dev] User-space RCU: call rcu_barrier() before dissociating helper thread? Mathieu Desnoyers via lttng-dev
2021-05-05  7:54   ` Martin Wilck via lttng-dev
2021-05-05 14:46     ` Mathieu Desnoyers via lttng-dev
2021-05-05 18:07       ` Paul E. McKenney via lttng-dev
2021-05-05 21:30       ` Martin Wilck via lttng-dev

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