[Qemu-devel] [PATCH 4/8] rcu: allow nesting of rcu_read_lock/rcu_read_unlock

[Paolo Bonzini <pbonzini@redhat.com>]

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 include/qemu/rcu.h | 15 ++++++++++++++-
 tests/rcutorture.c |  2 ++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
index 91b3a5c..e3d9b63 100644
--- a/include/qemu/rcu.h
+++ b/include/qemu/rcu.h
@@ -76,6 +76,9 @@ struct rcu_reader_data {
     unsigned long ctr;
     bool waiting;
 
+    /* Data used by reader only */
+    unsigned depth;
+
     /* Data used for registry, protected by rcu_gp_lock */
     QLIST_ENTRY(rcu_reader_data) node;
 };
@@ -85,8 +88,13 @@ extern __thread struct rcu_reader_data rcu_reader;
 static inline void rcu_read_lock(void)
 {
     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
+    unsigned ctr;
+
+    if (p_rcu_reader->depth++ > 0) {
+        return;
+    }
 
-    unsigned ctr = atomic_read(&rcu_gp_ctr);
+    ctr = atomic_read(&rcu_gp_ctr);
     atomic_xchg(&p_rcu_reader->ctr, ctr);
     if (atomic_read(&p_rcu_reader->waiting)) {
         atomic_set(&p_rcu_reader->waiting, false);
@@ -98,6 +106,11 @@ static inline void rcu_read_unlock(void)
 {
     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
 
+    assert(p_rcu_reader->depth != 0);
+    if (--p_rcu_reader->depth > 0) {
+        return;
+    }
+
     atomic_xchg(&p_rcu_reader->ctr, 0);
     if (atomic_read(&p_rcu_reader->waiting)) {
         atomic_set(&p_rcu_reader->waiting, false);
diff --git a/tests/rcutorture.c b/tests/rcutorture.c
index cda7458..a6ac2a9 100644
--- a/tests/rcutorture.c
+++ b/tests/rcutorture.c
@@ -257,9 +257,11 @@ static void *rcu_read_stress_test(void *arg)
         if (p->mbtest == 0) {
             n_mberror++;
         }
+        rcu_read_lock();
         for (i = 0; i < 100; i++) {
             garbage++;
         }
+        rcu_read_unlock();
         pc = p->pipe_count;
         rcu_read_unlock();
         if ((pc > RCU_STRESS_PIPE_LEN) || (pc < 0)) {
-- 
1.8.3.1