xs: avoid pthread_join deadlock in xs_daemon_close

Doing a pthread_cancel and join on the reader thread while holding all
the request/reply/watch mutexes can deadlock if the thread needs to
take any of those mutexes to exit.  Kill off the reader thread before
taking any mutexes (which should be redundant if we're
single-threaded at that point).

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
index 6a87ccf7085ddced019f94e21318f7da27fe741b..53e3d44345301a5f7333fe3248998829405c4555 100644 (file)
--- a/tools/xenstore/xs.c
+++ b/tools/xenstore/xs.c
@@ -260,10 +260,6 @@ void xs_daemon_destroy_postfork(struct xs_handle *h)
 
 void xs_daemon_close(struct xs_handle *h)
 {
-       mutex_lock(&h->request_mutex);
-       mutex_lock(&h->reply_mutex);
-       mutex_lock(&h->watch_mutex);
-
 #ifdef USE_PTHREAD
        if (h->read_thr_exists) {
                pthread_cancel(h->read_thr);
@@ -271,6 +267,10 @@ void xs_daemon_close(struct xs_handle *h)
        }
 #endif
 
+       mutex_lock(&h->request_mutex);
+       mutex_lock(&h->reply_mutex);
+       mutex_lock(&h->watch_mutex);
+
         close_free_msgs(h);
 
        mutex_unlock(&h->request_mutex);