[ltt-dev] Userspace RCU git fixes

[Mathieu Desnoyers]

Hi Paul, Hi Paolo,

Just to let you know that I pushed two updates into urcu: one fixes a
grace period hang caused by a missing wakeup in the synchronize_rcu QSBR
code. This appears to hit us due to the more fine-grained wakeup
code brought by Paolo. The wakeup was really missing from the
synchronize_rcu code (so Paolo's code just triggered an existing
problem). I thought it would be good to let you know the effect: grace
periods are delayed forever. This problem never appeared in a release (I
caught it before).

The second update registers the call_rcu worker threads as RCU reader
threads, so we can take the read-side lock inside them. I put them
offline when they wait, which makes them report quiescent state in QSBR.
This turns out to be required for my hash table code, and I think this
is generally a good thing.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com