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[Qemu-devel] [PATCH 3/3] rcu: detect missing rcu_register_thread()
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 3/3] rcu: detect missing rcu_register_thread() |
Date: |
Mon, 13 Jul 2015 13:31:05 +0200 |
Use an "impossible" value for the .depth field in order to quickly
detect threads that have not registered themselves with the RCU
subsystem.
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/rcu.h | 4 +++-
util/rcu.c | 18 ++++++++++++++++--
2 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
index 7df1e86..4facb35 100644
--- a/include/qemu/rcu.h
+++ b/include/qemu/rcu.h
@@ -82,7 +82,9 @@ static inline void rcu_read_lock(void)
struct rcu_reader_data *p_rcu_reader = &rcu_reader;
unsigned ctr;
- if (p_rcu_reader->depth++ > 0) {
+ p_rcu_reader->depth++;
+ assert(p_rcu_reader->depth >= 1);
+ if (p_rcu_reader->depth > 1) {
return;
}
diff --git a/util/rcu.c b/util/rcu.c
index 8830295..435cdbe 100644
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -63,8 +63,11 @@ static inline int rcu_gp_ongoing(unsigned long *ctr)
/* Written to only by each individual reader. Read by both the reader and the
* writers.
+ *
+ * Initializing the depth to -1 causes an assertion failure on the first
+ * call to rcu_read_lock() if the thread does not call rcu_register_thread().
*/
-__thread struct rcu_reader_data rcu_reader;
+__thread struct rcu_reader_data rcu_reader = { .depth = -1 };
/* Protected by rcu_gp_lock. */
typedef QLIST_HEAD(, rcu_reader_data) ThreadList;
@@ -277,7 +280,12 @@ static void rcu_unregister_thread_notify(Notifier *n, void
*data)
void rcu_register_thread(void)
{
- assert(rcu_reader.ctr == 0);
+ /* rcu_reader.depth is also used to detect whether the thread is
+ * registered.
+ */
+ assert(rcu_reader.depth == -1);
+ rcu_reader.depth = 0;
+
qemu_mutex_lock(&rcu_gp_lock);
QLIST_INSERT_HEAD(®istry, &rcu_reader, node);
qemu_mutex_unlock(&rcu_gp_lock);
@@ -288,6 +296,12 @@ void rcu_register_thread(void)
void rcu_unregister_thread(void)
{
+ /* Resetting the depth to -1 causes an assertion failure on the next
+ * call to rcu_read_lock().
+ */
+ assert(rcu_reader.depth == 0);
+ rcu_reader.depth = -1;
+
qemu_mutex_lock(&rcu_gp_lock);
QLIST_REMOVE(&rcu_reader, node);
qemu_mutex_unlock(&rcu_gp_lock);
--
2.4.3