monitor: protect mon->fds with mon_lock

mon->fds were protected by BQL.  Now protect it by mon_lock so that it
can even be used in monitor iothread.
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <20180608035511.7439-3-peterx@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

monitor.c

@@ -212,7 +212,6 @@ struct Monitor {
     BlockCompletionFunc *password_completion_cb;
     void *password_opaque;
     mon_cmd_t *cmd_table;
-    QLIST_HEAD(,mon_fd_t) fds;
     QTAILQ_ENTRY(Monitor) entry;
 
     /*
@@ -224,6 +223,7 @@ struct Monitor {
     /*
      * Fields that are protected by the per-monitor lock.
      */
+    QLIST_HEAD(, mon_fd_t) fds;
     QString *outbuf;
     guint out_watch;
     /* Read under either BQL or mon_lock, written with BQL+mon_lock.  */
@@ -2187,7 +2187,7 @@ static void hmp_acl_remove(Monitor *mon, const QDict *qdict)
 void qmp_getfd(const char *fdname, Error **errp)
 {
     mon_fd_t *monfd;
-    int fd;
+    int fd, tmp_fd;
 
     fd = qemu_chr_fe_get_msgfd(&cur_mon->chr);
     if (fd == -1) {
@@ -2202,13 +2202,17 @@ void qmp_getfd(const char *fdname, Error **errp)
         return;
     }
 
+    qemu_mutex_lock(&cur_mon->mon_lock);
     QLIST_FOREACH(monfd, &cur_mon->fds, next) {
         if (strcmp(monfd->name, fdname) != 0) {
             continue;
         }
 
-        close(monfd->fd);
+        tmp_fd = monfd->fd;
         monfd->fd = fd;
+        qemu_mutex_unlock(&cur_mon->mon_lock);
+        /* Make sure close() is out of critical section */
+        close(tmp_fd);
         return;
     }
 
@@ -2217,24 +2221,31 @@ void qmp_getfd(const char *fdname, Error **errp)
     monfd->fd = fd;
 
     QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
+    qemu_mutex_unlock(&cur_mon->mon_lock);
 }
 
 void qmp_closefd(const char *fdname, Error **errp)
 {
     mon_fd_t *monfd;
+    int tmp_fd;
 
+    qemu_mutex_lock(&cur_mon->mon_lock);
     QLIST_FOREACH(monfd, &cur_mon->fds, next) {
         if (strcmp(monfd->name, fdname) != 0) {
             continue;
         }
 
         QLIST_REMOVE(monfd, next);
-        close(monfd->fd);
+        tmp_fd = monfd->fd;
         g_free(monfd->name);
         g_free(monfd);
+        qemu_mutex_unlock(&cur_mon->mon_lock);
+        /* Make sure close() is out of critical section */
+        close(tmp_fd);
         return;
     }
 
+    qemu_mutex_unlock(&cur_mon->mon_lock);
     error_setg(errp, QERR_FD_NOT_FOUND, fdname);
 }
 
@@ -2242,6 +2253,7 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
 {
     mon_fd_t *monfd;
 
+    qemu_mutex_lock(&mon->mon_lock);
     QLIST_FOREACH(monfd, &mon->fds, next) {
         int fd;
 
@@ -2255,10 +2267,12 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
         QLIST_REMOVE(monfd, next);
         g_free(monfd->name);
         g_free(monfd);
+        qemu_mutex_unlock(&mon->mon_lock);
 
         return fd;
     }
 
+    qemu_mutex_unlock(&mon->mon_lock);
     error_setg(errp, "File descriptor named '%s' has not been found", fdname);
     return -1;
 }