Merge branch 'master' into urcu/ht-shrink

[urcu.git] / README

diff --git a/README b/README
index 44a4bf574876ec222d00f7fa6123ccd88f3086d0..e3800faad2d10cc5789c0a622c14f5ade9962ae1 100644 (file)
--- a/README
+++ b/README
@@ -39,6 +39,8 @@ supported, with the following exceptions:
   therefore not compatible with liburcu on x86 32-bit (i386, i486, i586, i686).
   The problem has been reported to the gcc community:
     http://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg281255.html
+- gcc 3.3 cannot match the "xchg" instruction on 32-bit x86 build.
+  See: http://kerneltrap.org/node/7507
 - Alpha, ia64 and ARM architectures depend on 4.x gcc with atomic builtins
   support.
 
@@ -185,6 +187,15 @@ Interaction with mutexes
        mutex in its dependency chain) should not be acquired from within a RCU
        read-side critical section.
 
+       This is especially important to understand in the context of the
+       QSBR flavor: a registered reader thread being "online" by
+       default should be considered as within a RCU read-side critical
+       section unless explicitly put "offline". Therefore, if
+       synchronize_rcu() is called with a mutex held, this mutex, as
+       well as any mutex which has this mutex in its dependency chain
+       should only be taken when the RCU reader thread is "offline"
+       (this can be performed by calling rcu_thread_offline()).
+
 Usage of DEBUG_RCU
 
        DEBUG_RCU is used to add internal debugging self-checks to the