From: Mathieu Desnoyers Date: Tue, 15 Sep 2009 20:39:35 +0000 (-0400) Subject: qsbr urcu: make it safe to call rcu_sychronize from a registered thread X-Git-Tag: v0.1~90 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=ff2f67a0a2168bb1f0114af901e5e8e6ddce076b;p=userspace-rcu.git qsbr urcu: make it safe to call rcu_sychronize from a registered thread Actually, the proper way to deal with threads registered as readers but also calling synchronize_rcu() is to mark them as offline while the synchronize is in progress. Else, since calling rcu_sychronize will increment urcu_gp_ctr, we will be stupidly waiting for ourselves and deadlock. Original-patch-from: Pierre Habouzit Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu-qsbr.c b/urcu-qsbr.c index c0f0554..4ce2f9a 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -148,12 +148,27 @@ static void wait_for_quiescent_state(void) void synchronize_rcu(void) { + int was_online; + + was_online = rcu_reader_qs_gp & 1; + + /* + * Mark the writer thread offline to make sure we don't wait for + * our own quiescent state. This allows using synchronize_rcu() in + * threads registered as readers. + */ + if (was_online) + _rcu_thread_offline(); + internal_urcu_lock(); force_mb_all_threads(); urcu_gp_ctr += 2; wait_for_quiescent_state(); force_mb_all_threads(); internal_urcu_unlock(); + + if (was_online) + _rcu_thread_online(); } /*