commit d62cb4f2fdc0977f9ca9f41d297c3d2c44874171
author Paolo Bonzini <pbonzini@redhat.com> Tue Jan 13 17:34:15 2015 +0100
committer Paolo Bonzini <pbonzini@redhat.com> Mon Feb 02 16:55:10 2015 +0100
tree cad4b85fa5ddff699506743187e746e5e456231c
parent 8fda74a52bf3fa63cb80c877b6946cb9143f96cc

rcu: allow nesting of rcu_read_lock/rcu_read_unlock

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu/rcu.h

diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
index cfef36e..da043f2 100644
--- a/include/qemu/rcu.h
+++ b/include/qemu/rcu.h
@@ -68,6 +68,9 @@
     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;
 };
@@ -77,8 +80,13 @@
 static inline void rcu_read_lock(void)
 {
     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
+    unsigned ctr;
 
-    unsigned ctr = atomic_read(&rcu_gp_ctr);
+    if (p_rcu_reader->depth++ > 0) {
+        return;
+    }
+
+    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);
@@ -90,6 +98,11 @@
 {
     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);

tests/rcutorture.c

diff --git a/tests/rcutorture.c b/tests/rcutorture.c
index cb78411..60a2ccf 100644
--- a/tests/rcutorture.c
+++ b/tests/rcutorture.c
@@ -255,9 +255,11 @@
         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)) {