QemuMutex: support --enable-debug-mutex

We have had some tracing tools for mutex but it's not easy to use them
for e.g. dead locks.  Let's provide "--enable-debug-mutex" parameter
when configure to allow QemuMutex to store the last owner that took
specific lock.  It will be easy to use this tool to debug deadlocks
since we can directly know who took the lock then as long as we can have
a debugger attached to the process.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180425025459.5258-4-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/util/qemu-thread-common.h b/util/qemu-thread-common.h
index d329208..a0ea7c0 100644
--- a/util/qemu-thread-common.h
+++ b/util/qemu-thread-common.h
@@ -19,6 +19,10 @@
 
 static inline void qemu_mutex_post_init(QemuMutex *mutex)
 {
+#ifdef CONFIG_DEBUG_MUTEX
+    mutex->file = NULL;
+    mutex->line = 0;
+#endif
     mutex->initialized = true;
 }
 
@@ -31,12 +35,20 @@ static inline void qemu_mutex_pre_lock(QemuMutex *mutex,
 static inline void qemu_mutex_post_lock(QemuMutex *mutex,
                                         const char *file, int line)
 {
+#ifdef CONFIG_DEBUG_MUTEX
+    mutex->file = file;
+    mutex->line = line;
+#endif
     trace_qemu_mutex_locked(mutex, file, line);
 }
 
 static inline void qemu_mutex_pre_unlock(QemuMutex *mutex,
                                          const char *file, int line)
 {
+#ifdef CONFIG_DEBUG_MUTEX
+    mutex->file = NULL;
+    mutex->line = 0;
+#endif
     trace_qemu_mutex_unlock(mutex, file, line);
 }