[Qemu-devel] [RFC PATCH 04/14] qemu-thread: register threads with RCU

[Mike Day <ncmike@ncultra.org>]

From: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Mike Day <ncmike@ncultra.org>
---
 docs/rcu.txt             | 13 +++++++------
 util/qemu-thread-posix.c | 28 +++++++++++++++++++++++++++-
 util/qemu-thread-win32.c |  2 ++
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/docs/rcu.txt b/docs/rcu.txt
index 19e4840..5736676 100644
--- a/docs/rcu.txt
+++ b/docs/rcu.txt
@@ -122,8 +122,8 @@ on many POSIX systems other than Linux and Solaris).
 
 For this reason, QEMU's RCU implementation resorts to manual annotation
 of "quiescent states", i.e. points where no RCU read-side critical
-section can be active.  All threads that participate in the RCU mechanism
-need to annotate such points.
+section can be active.  All threads created with qemu_thread_create
+participate in the RCU mechanism and need to annotate such points.
 
 Marking quiescent states is done with the following three APIs:
 
@@ -144,8 +144,8 @@ Marking quiescent states is done with the following three APIs:
         thread.
 
 
-Furthermore, threads that participate in the RCU mechanism must communicate
-this fact using the following APIs:
+The following APIs can be used to use RCU in a thread that is not
+created with qemu_thread_create():
 
      void rcu_register_thread(void);
 
@@ -160,8 +160,9 @@ this fact using the following APIs:
         either manually or by using the QemuCond/QemuSemaphore/QemuEvent
         APIs.
 
-Note that these APIs are relatively heavyweight, and should _not_ be
-nested.
+Note that these APIs are relatively heavyweight, should _not_ be
+nested, and should not be called in threads that are created with
+qemu_thread_create().
 
 
 DIFFERENCES WITH LINUX
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index 37dd298..2371176 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -26,6 +26,7 @@
 #endif
 #include "qemu/thread.h"
 #include "qemu/atomic.h"
+#include "qemu/rcu.h"
 
 static void error_exit(int err, const char *msg)
 {
@@ -388,6 +389,26 @@ void qemu_event_wait(QemuEvent *ev)
 }
 
 
+typedef struct QemuThreadData {
+    /* Passed to win32_start_routine.  */
+    void             *(*start_routine)(void *);
+    void             *arg;
+} QemuThreadData;
+
+static void *thread_start_routine(void *arg)
+{
+    QemuThreadData *data = (QemuThreadData *) arg;
+    void *(*start_routine)(void *) = data->start_routine;
+    void *thread_arg = data->arg;
+    void *ret;
+
+    rcu_register_thread();
+    g_free(data);
+    ret = start_routine(thread_arg);
+    rcu_unregister_thread();
+    return ret;
+}
+
 void qemu_thread_create(QemuThread *thread,
                        void *(*start_routine)(void*),
                        void *arg, int mode)
@@ -395,6 +416,11 @@ void qemu_thread_create(QemuThread *thread,
     sigset_t set, oldset;
     int err;
     pthread_attr_t attr;
+    QemuThreadData *data;
+
+    data = g_malloc(sizeof(*data));
+    data->start_routine = start_routine;
+    data->arg = arg;
 
     err = pthread_attr_init(&attr);
     if (err) {
@@ -410,7 +436,7 @@ void qemu_thread_create(QemuThread *thread,
     /* Leave signal handling to the iothread.  */
     sigfillset(&set);
     pthread_sigmask(SIG_SETMASK, &set, &oldset);
-    err = pthread_create(&thread->thread, &attr, start_routine, arg);
+    err = pthread_create(&thread->thread, &attr, thread_start_routine, data);
     if (err)
         error_exit(err, __func__);
 
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index 27a5217..0c4850d 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -278,6 +278,7 @@ static unsigned __stdcall win32_start_routine(void *arg)
         data = NULL;
     }
     qemu_thread_data = data;
+    rcu_register_thread();
     qemu_thread_exit(start_routine(thread_arg));
     abort();
 }
@@ -293,6 +294,7 @@ void qemu_thread_exit(void *arg)
         data->exited = true;
         LeaveCriticalSection(&data->cs);
     }
+    rcu_unregister_thread();
     _endthreadex(0);
 }
 
-- 
1.8.3.1