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[Qemu-devel] [PULL 08/11] rcu: detect missing rcu_register_thread()
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 08/11] rcu: detect missing rcu_register_thread() |
Date: |
Thu, 16 Jul 2015 18:55:55 +0200 |
Use an "impossible" value for the .depth field in order to quickly
detect threads that have not registered themselves with the RCU
subsystem.
Avoid a false positive around forking by unregistering and registering
the forking thread explicitly. Previously, it was enough to re-register
the thread.
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/rcu.h | 4 +++-
util/rcu.c | 35 ++++++++++++++++++++++++++++++-----
2 files changed, 33 insertions(+), 6 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 e21bb46..2490273 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;
@@ -279,7 +282,12 @@ 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);
@@ -290,6 +298,12 @@ 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);
@@ -301,7 +315,6 @@ static void rcu_init_complete(void)
{
QemuThread thread;
- qemu_mutex_init(&rcu_gp_lock);
qemu_event_init(&rcu_gp_event, true);
qemu_event_init(&rcu_call_ready_event, false);
@@ -311,8 +324,6 @@ static void rcu_init_complete(void)
*/
qemu_thread_create(&thread, "call_rcu", call_rcu_thread,
NULL, QEMU_THREAD_DETACHED);
-
- rcu_register_thread();
}
#ifdef CONFIG_POSIX
@@ -329,14 +340,28 @@ static void rcu_init_unlock(void)
void rcu_after_fork(void)
{
+ int save_depth = rcu_reader.depth;
+ if (save_depth != -1) {
+ rcu_unregister_thread();
+ }
+
memset(®istry, 0, sizeof(registry));
+
rcu_init_complete();
+
+ if (save_depth != -1) {
+ rcu_register_thread();
+ rcu_reader.depth = save_depth;
+ }
}
static void __attribute__((__constructor__)) rcu_init(void)
{
+ qemu_mutex_init(&rcu_gp_lock);
#ifdef CONFIG_POSIX
pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_unlock);
#endif
rcu_init_complete();
+
+ rcu_register_thread();
}
--
2.4.3
- [Qemu-devel] [PULL 00/11] RCU, KVM, memory API, crypto, Coverity fixes for 2.4.0-rc1, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 01/11] mips/kvm: Fix Big endian 32-bit register access, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 02/11] mips/kvm: Sign extend registers written to KVM, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 03/11] ppc/spapr_drc: fix memory leak, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 04/11] arm/xlnx-zynqmp: fix memory leak, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 05/11] RDMA: Fix error exits, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 07/11] rcu: actually register threads that have RCU read-side critical sections, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 06/11] rcu: automatically unregister threads when they exit, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 08/11] rcu: detect missing rcu_register_thread(),
Paolo Bonzini <=
- [Qemu-devel] [PULL 10/11] crypto: fix build with nettle >= 3.0.0, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 09/11] memory: fix refcount leak in memory_region_present, Paolo Bonzini, 2015/07/16
- [Qemu-devel] [PULL 11/11] crypto: avoid undefined behavior in nettle calls, Paolo Bonzini, 2015/07/16
- Re: [Qemu-devel] [PULL 00/11] RCU, KVM, memory API, crypto, Coverity fixes for 2.4.0-rc1, Peter Maydell, 2015/07/16