[Qemu-devel] [PATCH v3 2/3] QemuMutex: support --enable-debug-mutex

[Peter Xu <peterx@redhat.com>]

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.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 configure                   | 10 ++++++++++
 include/qemu/thread-posix.h |  4 ++++
 include/qemu/thread-win32.h |  4 ++++
 util/qemu-thread-common.c   |  8 ++++++++
 4 files changed, 26 insertions(+)

diff --git a/configure b/configure
index 0a19b033bc..a80af735b2 100755
--- a/configure
+++ b/configure
@@ -451,6 +451,7 @@ jemalloc="no"
 replication="yes"
 vxhs=""
 libxml2=""
+debug_mutex="no"
 
 supported_cpu="no"
 supported_os="no"
@@ -1374,6 +1375,10 @@ for opt do
   ;;
   --disable-git-update) git_update=no
   ;;
+  --enable-debug-mutex) debug_mutex=yes
+  ;;
+  --disable-debug-mutex) debug_mutex=no
+  ;;
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1631,6 +1636,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   crypto-afalg    Linux AF_ALG crypto backend driver
   vhost-user      vhost-user support
   capstone        capstone disassembler support
+  debug-mutex     mutex debugging support
 
 NOTE: The object files are built at the place where configure is launched
 EOF
@@ -5874,6 +5880,7 @@ echo "avx2 optimization $avx2_opt"
 echo "replication support $replication"
 echo "VxHS block device $vxhs"
 echo "capstone          $capstone"
+echo "mutex debugging   $debug_mutex"
 
 if test "$sdl_too_old" = "yes"; then
 echo "-> Your SDL version is too old - please upgrade to have SDL support"
@@ -6602,6 +6609,9 @@ fi
 if test "$capstone" != "no" ; then
   echo "CONFIG_CAPSTONE=y" >> $config_host_mak
 fi
+if test "$debug_mutex" = "yes" ; then
+  echo "CONFIG_DEBUG_MUTEX=y" >> $config_host_mak
+fi
 
 # Hold two types of flag:
 #   CONFIG_THREAD_SETNAME_BYTHREAD  - we've got a way of setting the name on
diff --git a/include/qemu/thread-posix.h b/include/qemu/thread-posix.h
index f3f47e426f..fd27b34128 100644
--- a/include/qemu/thread-posix.h
+++ b/include/qemu/thread-posix.h
@@ -12,6 +12,10 @@ typedef QemuMutex QemuRecMutex;
 
 struct QemuMutex {
     pthread_mutex_t lock;
+#ifdef CONFIG_DEBUG_MUTEX
+    const char *file;
+    int line;
+#endif
     bool initialized;
 };
 
diff --git a/include/qemu/thread-win32.h b/include/qemu/thread-win32.h
index 3a05e3b3aa..d668d789b4 100644
--- a/include/qemu/thread-win32.h
+++ b/include/qemu/thread-win32.h
@@ -5,6 +5,10 @@
 
 struct QemuMutex {
     SRWLOCK lock;
+#ifdef CONFIG_DEBUG_MUTEX
+    const char *file;
+    int line;
+#endif
     bool initialized;
 };
 
diff --git a/util/qemu-thread-common.c b/util/qemu-thread-common.c
index fc1f1aa969..fb88bf111c 100644
--- a/util/qemu-thread-common.c
+++ b/util/qemu-thread-common.c
@@ -21,10 +21,18 @@ void qemu_mutex_pre_lock(QemuMutex *mutex, const char *file, int line)
 
 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);
 }
 
 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);
 }
-- 
2.14.3