README: discuss mutex vs RCU interaction

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/README b/README
index b3839e1a614a134c4960cc96824cefca83078d69..a2ca1eb147a7318845ac0da336ff40ba5ba86f22 100644 (file)
--- a/README
+++ b/README
@@ -146,6 +146,14 @@ Being careful with signals
        rcu_quiescent_state() calls, when threads are put offline and around
        calls to synchronize_rcu(). Even then, we do not recommend it.
 
+Interaction with mutexes
+
+       One must be careful to do not cause deadlocks due to interaction of
+       synchronize_rcu() and RCU read-side with mutexes. If synchronize_rcu()
+       is called with a mutex held, this mutex (or any mutex which has this
+       mutex in its dependency chain) should not be acquired from within a RCU
+       read-side critical section.
+
 Usage of DEBUG_RCU
 
        DEBUG_RCU is used to add internal debugging self-checks to the