From c4c303c7c5679b4b368e12f41124aee29c325b76 Mon Sep 17 00:00:00 2001
From: Olaf Hering <olaf@aepfle.de>
Date: Thu, 25 Aug 2011 18:30:11 +0200
Subject: [PATCH] xen/pv-on-hvm kexec: prevent crash in xenwatch_thread() when
stale watch events arrive
During repeated kexec boots xenwatch_thread() can crash because
xenbus_watch->callback is cleared by xenbus_watch_path() if a node/token
combo for a new watch happens to match an already registered watch from
an old kernel. In this case xs_watch returns -EEXISTS, then
register_xenbus_watch() does not remove the to-be-registered watch from
the list of active watches but returns the -EEXISTS to the caller
anyway.
Because the watch is still active in xenstored it will cause an event
which will arrive in the new kernel. process_msg() will find the
encapsulated struct xenbus_watch in its list of registered watches and
puts the "empty" watch handle in the queue for xenwatch_thread().
xenwatch_thread() then calls ->callback which was cleared earlier by
xenbus_watch_path().
To prevent that crash in a guest running on an old xen toolstack remove
the special -EEXIST handling.
v2:
- remove the EEXIST handing in register_xenbus_watch() instead of
checking for ->callback in process_msg()
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
drivers/xen/xenbus/xenbus_xs.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index 5534690075af..46347a49c5b8 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -638,8 +638,7 @@ int register_xenbus_watch(struct xenbus_watch *watch)
err = xs_watch(watch->node, token);
- /* Ignore errors due to multiple registration. */
- if ((err != 0) && (err != -EEXIST)) {
+ if (err) {
spin_lock(&watches_lock);
list_del(&watch->list);
spin_unlock(&watches_lock);
--
2.34.1