[Xen-devel] [PATCH 2 of 2] xs: avoid pthread_join deadlock in xs_daemon_close

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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@xxxxxxxxxx>

diff -r 84ee0559ddc1 tools/xenstore/xs.c
--- a/tools/xenstore/xs.c       Tue May 11 14:55:14 2010 -0700
+++ b/tools/xenstore/xs.c       Tue May 11 14:55:20 2010 -0700
@@ -260,10 +260,6 @@
 
 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 @@
        }
 #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);



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