[Qemu-devel] [PATCH] cpus: make qemu_mutex_iothread_locked() understand co-routines

["Alex Bennée" <alex.bennee@linaro.org>]

There is a slight wart when checking for the state of the BQL when using
GThread base co-routines (which we keep for ThreadSanitizer runs). While
the main-loop holds the BQL it is suspended until the co-routine
completes however the co-routines run in a separate thread so checking
the TLS variable could be wrong.

We fix this by expanding the check to include qemu_in_coroutine() for
GThread based builds. As it is not used for production builds I'm not
overly worried about any performance impact which should be negligible
anyway.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
---
 configure |  3 +++
 cpus.c    | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/configure b/configure
index 91a14c1..97b89fb 100755
--- a/configure
+++ b/configure
@@ -5461,6 +5461,9 @@ if test "$rbd" = "yes" ; then
 fi
 
 echo "CONFIG_COROUTINE_BACKEND=$coroutine" >> $config_host_mak
+if test "$coroutine" = "gthread" ; then
+  echo "CONFIG_COROUTINE_GTHREAD=1" >> $config_host_mak
+fi
 if test "$coroutine_pool" = "yes" ; then
   echo "CONFIG_COROUTINE_POOL=1" >> $config_host_mak
 else
diff --git a/cpus.c b/cpus.c
index 0c18a9f..a3e189a 100644
--- a/cpus.c
+++ b/cpus.c
@@ -49,6 +49,10 @@
 #include "hw/nmi.h"
 #include "sysemu/replay.h"
 
+#ifdef CONFIG_COROUTINE_GTHREAD
+#include "qemu/coroutine.h"
+#endif
+
 #ifndef _WIN32
 #include "qemu/compatfd.h"
 #endif
@@ -1422,9 +1426,18 @@ bool qemu_in_vcpu_thread(void)
 
 static __thread bool iothread_locked = false;
 
+/*
+ * There is a slight wart when using gthread based co-routines. Here
+ * the BQL is held by the main-thread which is suspended until the
+ * co-routines complete.
+ */
 bool qemu_mutex_iothread_locked(void)
 {
+#ifdef CONFIG_COROUTINE_GTHREAD
+    return iothread_locked || qemu_in_coroutine();
+#else
     return iothread_locked;
+#endif
 }
 
 void qemu_mutex_lock_iothread(void)
-- 
2.9.3