* Paul E. McKenney (paul...@linux.vnet.ibm.com) wrote:
This commit ensures that all read-side functions meet the 10-line LGPL
criterion that permits them to be expanded directly into non-LGPL code,
without function-call instructions. It also documents this as the intent.
Signed-off-by: Paul E. McKenney paul...@linux.vnet.ibm.com
diff --git a/urcu/static/urcu-bp.h b/urcu/static/urcu-bp.h
index e7b2eda..881b4a4 100644
--- a/urcu/static/urcu-bp.h
+++ b/urcu/static/urcu-bp.h
@@ -6,8 +6,8 @@
*
* Userspace RCU header.
*
- * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
- * dynamically with the userspace rcu library.
+ * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
+ * RELEASE. See urcu.h for linking dynamically with the userspace rcu
library.
*
* Copyright (c) 2009 Mathieu Desnoyers mathieu.desnoy...@efficios.com
* Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
@@ -162,32 +162,48 @@ static inline int rcu_old_gp_ongoing(long *value)
((v ^ rcu_gp_ctr) RCU_GP_CTR_PHASE);
}
+/*
+ * Helper for _rcu_read_lock(). The format of rcu_gp_ctr (as well as
+ * the per-thread rcu_reader.ctr) has the upper bits containing a count of
+ * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
+ * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in
+ * _rcu_read_lock() happen before the subsequent read-side critical section.
+ */
+static inline void _rcu_read_lock_help(unsigned long tmp)
could we rename the _rcu_read_lock_help to _rcu_read_lock_update ?
I think it would fit better the role of this function in the algorithm.
As Josh pointed out, directloy - directly below,
The rest looks good. I'll wait for an updated version.
Thanks !
Mathieu
+{
+ if (caa_likely(!(tmp RCU_GP_CTR_NEST_MASK))) {
+ _CMM_STORE_SHARED(URCU_TLS(rcu_reader)-ctr,
_CMM_LOAD_SHARED(rcu_gp_ctr));
+ cmm_smp_mb();
+ } else
+ _CMM_STORE_SHARED(URCU_TLS(rcu_reader)-ctr, tmp +
RCU_GP_COUNT);
+}
+
+/*
+ * Enter an RCU read-side critical section.
+ *
+ * The first cmm_barrier() call ensures that the compiler does not reorder
+ * the body of _rcu_read_lock() with a mutex.
+ *
+ * This function and its helper are both less than 10 lines long. The
+ * intent is that this function meets the 10-line criterion in LGPL,
+ * allowing this function to be invoked directly from non-LGPL code.
+ */
static inline void _rcu_read_lock(void)
{
long tmp;
- /* Check if registered */
if (caa_unlikely(!URCU_TLS(rcu_reader)))
- rcu_bp_register();
-
+ rcu_bp_register(); /* If not yet registered. */
cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
tmp = URCU_TLS(rcu_reader)-ctr;
- /*
- * rcu_gp_ctr is
- * RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE)
- */
- if (caa_likely(!(tmp RCU_GP_CTR_NEST_MASK))) {
- _CMM_STORE_SHARED(URCU_TLS(rcu_reader)-ctr,
_CMM_LOAD_SHARED(rcu_gp_ctr));
- /*
- * Set active readers count for outermost nesting level before
- * accessing the pointer.
- */
- cmm_smp_mb();
- } else {
- _CMM_STORE_SHARED(URCU_TLS(rcu_reader)-ctr, tmp +
RCU_GP_COUNT);
- }
+ _rcu_read_lock_help(tmp);
}
+/*
+ * Exit an RCU read-side critical section. This function is less than
+ * 10 lines of code, and is intended to be usable by non-LGPL code, as
+ * called out in LGPL.
+ */
static inline void _rcu_read_unlock(void)
{
/*
diff --git a/urcu/static/urcu-pointer.h b/urcu/static/urcu-pointer.h
index 48dc5bf..0ddf6a1 100644
--- a/urcu/static/urcu-pointer.h
+++ b/urcu/static/urcu-pointer.h
@@ -6,8 +6,8 @@
*
* Userspace RCU header. Operations on pointers.
*
- * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-pointer.h for
- * linking dynamically with the userspace rcu library.
+ * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
+ * RELEASE. See urcu.h for linking dynamically with the userspace rcu
library.
*
* Copyright (c) 2009 Mathieu Desnoyers mathieu.desnoy...@efficios.com
* Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
@@ -59,8 +59,11 @@ extern C {
* addition to forthcoming C++ standard.
*
* Should match rcu_assign_pointer() or rcu_xchg_pointer().
+ *
+ * This macro is less than 10 lines long. The intent is that this macro
+ * meets the 10-line criterion in LGPL, allowing this function to be
+ * expanded directloy in non-LGPL code.
*/
-
#define _rcu_dereference(p) ({ \
__typeof__(p) _p1 = CMM_LOAD_SHARED(p);
\
cmm_smp_read_barrier_depends(); \
@@ -73,8 +76,11 @@ extern C {
* data structure,
