From: SeongJae Park <sjpark@xxxxxxxxx>
This commit adds a counter of pending messages for each watch in the
struct. It is used to skip unnecessary pending messages lookup in
'unregister_xenbus_watch()'. It could also be used in 'will_handle'
callback.
This is part of XSA-349
This is upstream commit 3dc86ca6b4c8cfcba9da7996189d1b5a358a94fc
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
Reported-by: Michael Kurth <mku@xxxxxxxxx>
Reported-by: Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
drivers/xen/xenbus/xenbus_xs.c | 30 ++++++++++++++++++------------
include/xen/xenbus.h | 2 ++
2 files changed, 20 insertions(+), 12 deletions(-)
diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index 0ea1c259f2f1..420d478e1708 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -701,6 +701,8 @@ int register_xenbus_watch(struct xenbus_watch *watch)
sprintf(token, "%lX", (long)watch);
+ watch->nr_pending = 0;
+
down_read(&xs_state.watch_mutex);
spin_lock(&watches_lock);
@@ -750,12 +752,15 @@ void unregister_xenbus_watch(struct xenbus_watch *watch)
/* Cancel pending watch events. */
spin_lock(&watch_events_lock);
- list_for_each_entry_safe(msg, tmp, &watch_events, list) {
- if (msg->u.watch.handle != watch)
- continue;
- list_del(&msg->list);
- kfree(msg->u.watch.vec);
- kfree(msg);
+ if (watch->nr_pending) {
+ list_for_each_entry_safe(msg, tmp, &watch_events, list) {
+ if (msg->u.watch.handle != watch)
+ continue;
+ list_del(&msg->list);
+ kfree(msg->u.watch.vec);
+ kfree(msg);
+ }
+ watch->nr_pending = 0;
}
spin_unlock(&watch_events_lock);
@@ -802,7 +807,6 @@ void xs_suspend_cancel(void)
static int xenwatch_thread(void *unused)
{
- struct list_head *ent;
struct xs_stored_msg *msg;
for (;;) {
@@ -815,13 +819,15 @@ static int xenwatch_thread(void *unused)
mutex_lock(&xenwatch_mutex);
spin_lock(&watch_events_lock);
- ent = watch_events.next;
- if (ent != &watch_events)
- list_del(ent);
+ msg = list_first_entry_or_null(&watch_events,
+ struct xs_stored_msg, list);
+ if (msg) {
+ list_del(&msg->list);
+ msg->u.watch.handle->nr_pending--;
+ }
spin_unlock(&watch_events_lock);
- if (ent != &watch_events) {
- msg = list_entry(ent, struct xs_stored_msg, list);
+ if (msg) {
msg->u.watch.handle->callback(
msg->u.watch.handle,
(const char **)msg->u.watch.vec,
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 1772507dc2c9..ed9e7e3307b7 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -58,6 +58,8 @@ struct xenbus_watch
/* Path being watched. */
const char *node;
+ unsigned int nr_pending;
+
/*
* Called just before enqueing new event while a spinlock is held.
* The event will be discarded if this callback returns false.
--
2.17.1
