Re: [libvirt] [PATCH 3/5] tests: avoid segfault if json monitor not present

On a machine without json headers, I was seeing random segfaults from qemumonitorjsontest (about 90% of the runs on my particular machine). The segfault was inside virClassIsDerivedFrom, which points to a case of a race leading to unreferencing a stale pointer to an object that had already been freed. I also noticed that if I got the segfault, I was seeing messages such as: 2013-02-22 16:12:37.504+0000: 19833: error : virNetSocketWriteWire:1361 : Cannot write data: Bad file descriptor which is also evidence of deferencing a stale pointer. I traced it to a race where qemuMonitorTestIO could execute late, after the main thread had already called qemuMonitorTestFree and called virNetSocketClose(test->client) but not clearing it out to NULL. Sure enough, after test->client has been closed, fd is -1, which causes an attempt to write to the socket to fail, which in turn triggers the error code of qemuMonitorTestIO that tries to re-close test->client. * tests/qemumonitortestutils.c (qemuMonitorTestIO): Don't attempt to free client again if test already quit. --- tests/qemumonitortestutils.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/tests/qemumonitortestutils.c b/tests/qemumonitortestutils.c index 1ed42ce..979623a 100644 --- a/tests/qemumonitortestutils.c +++ b/tests/qemumonitortestutils.c @@ -214,6 +214,10 @@ static void qemuMonitorTestIO(virNetSocketPtr sock, bool err = false; virMutexLock(&test->lock); + if (test->quit) { + virMutexUnlock(&test->lock); + return; + } if (events & VIR_EVENT_HANDLE_WRITABLE) { ssize_t ret; if ((ret = virNetSocketWrite(sock,