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authorJuergen Gross <jgross@suse.com>2017-07-28 16:53:55 +0200
committerJuergen Gross <jgross@suse.com>2017-08-11 16:45:56 +0200
commit529871bb3c0675d0b425e2070d5a739db097be98 (patch)
tree0422815a0e9fe13f44bebde0046b768569ea36e9
parent4ca83dcf4e3bc0c98836dbb97553792ca7ea5429 (diff)
downloadlinux-stericsson-529871bb3c0675d0b425e2070d5a739db097be98.tar.gz
xen: avoid deadlock in xenbus
When starting the xenwatch thread a theoretical deadlock situation is possible: xs_init() contains: task = kthread_run(xenwatch_thread, NULL, "xenwatch"); if (IS_ERR(task)) return PTR_ERR(task); xenwatch_pid = task->pid; And xenwatch_thread() does: mutex_lock(&xenwatch_mutex); ... event->handle->callback(); ... mutex_unlock(&xenwatch_mutex); The callback could call unregister_xenbus_watch() which does: ... if (current->pid != xenwatch_pid) mutex_lock(&xenwatch_mutex); ... In case a watch is firing before xenwatch_pid could be set and the callback of that watch unregisters a watch, then a self-deadlock would occur. Avoid this by setting xenwatch_pid in xenwatch_thread(). Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by: Juergen Gross <jgross@suse.com>
-rw-r--r--drivers/xen/xenbus/xenbus_xs.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index e46080214955..3e59590c7254 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -857,6 +857,8 @@ static int xenwatch_thread(void *unused)
struct list_head *ent;
struct xs_watch_event *event;
+ xenwatch_pid = current->pid;
+
for (;;) {
wait_event_interruptible(watch_events_waitq,
!list_empty(&watch_events));
@@ -925,7 +927,6 @@ int xs_init(void)
task = kthread_run(xenwatch_thread, NULL, "xenwatch");
if (IS_ERR(task))
return PTR_ERR(task);
- xenwatch_pid = task->pid;
/* shutdown watches for kexec boot */
xs_reset_watches();