Update urcu and urcu-qsbr, make compiler barriers explicit

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index b8567555d09ecbb22547aa6f236392d439eea871..c6d7dbc9d83a011a7b7d2885f93460a268da6ea2 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -208,13 +208,15 @@ void update_counter_and_wait(void)
        STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
 
        /*
-        * Must commit qparity update to memory before waiting for other parity
-        * quiescent state. Failure to do so could result in the writer waiting
-        * forever while new readers are always accessing data (no progress).
-        * Ensured by STORE_SHARED and LOAD_SHARED.
+        * Must commit rcu_gp_ctr update to memory before waiting for quiescent
+        * state. Failure to do so could result in the writer waiting forever
+        * while new readers are always accessing data (no progress). Enforce
+        * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
         */
+       barrier();
 
        /*
+        *
         * Adding a smp_mb() which is _not_ formally required, but makes the
         * model easier to understand. It does not have a big performance impact
         * anyway, given this is the write-side.
@@ -302,11 +304,12 @@ void synchronize_rcu(void)
 
        /*
         * Must finish waiting for quiescent state for parity 0 before
-        * committing qparity update to memory. Failure to do so could result in
-        * the writer waiting forever while new readers are always accessing
-        * data (no progress).
-        * Ensured by STORE_SHARED and LOAD_SHARED.
+        * committing next rcu_gp_ctr update to memory. Failure to do so could
+        * result in the writer waiting forever while new readers are always
+        * accessing data (no progress).  Enforce compiler-order of load
+        * rcu_reader ctr before store to rcu_gp_ctr.
         */
+       barrier();
 
        /*
         * Adding a smp_mb() which is _not_ formally required, but makes the