[lttng-dev] URCU and pthread mutex/cond variable hang

[Jeff Layton]

I've been using urcu to develop some userland code, and I've run into a
problem that I don't quite understand. If I register a thread and then
have that thread block on a pthread condition variable, then it seems
to cause synchronize_rcu in another thread to hang.

I've attached a testcase that demonstrates the problem. You have to
build it and link it against -lpthread and -lurcu-qsbr:

    $ gcc -Wall -o ./urcu_hang -lpthread -lurcu-qsbr urcu_hang.c

...it will run fine. If you comment out the rcu_thread_offline/online
calls though, it will hang.

Why? Is this expected behavior or a bug in urcu?

Thanks in advance!
-- 
Jeff Layton <jlayton at poochiereds.net>
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