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xen/xenbus: Count pending messages for each watch

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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

Cc: stable@vger.kernel.org
Signed-off-by: SeongJae Park <sjpark@amazon.de>
Reported-by: Michael Kurth <mku@amazon.de>
Reported-by: Pawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
SeongJae Park 2020-12-14 10:07:13 +01:00 committed by Juergen Gross
parent be987200fb
commit 3dc86ca6b4
2 changed files with 20 additions and 11 deletions
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19
drivers/xen/xenbus/xenbus_xs.c
View File

@ -711,6 +711,7 @@ int xs_watch_msg(struct xs_watch_event *event)
event->path, event->token))) {
spin_lock(&watch_events_lock);
list_add_tail(&event->list, &watch_events);
event->handle->nr_pending++;
wake_up(&watch_events_waitq);
spin_unlock(&watch_events_lock);
} else
@ -768,6 +769,8 @@ int register_xenbus_watch(struct xenbus_watch *watch)
sprintf(token, "%lX", (long)watch);
watch->nr_pending = 0;
down_read(&xs_watch_rwsem);
spin_lock(&watches_lock);
@ -817,12 +820,15 @@ void unregister_xenbus_watch(struct xenbus_watch *watch)
/* Cancel pending watch events. */
spin_lock(&watch_events_lock);
if (watch->nr_pending) {
list_for_each_entry_safe(event, tmp, &watch_events, list) {
if (event->handle != watch)
continue;
list_del(&event->list);
kfree(event);
}
watch->nr_pending = 0;
}
spin_unlock(&watch_events_lock);
if (current->pid != xenwatch_pid)
@ -868,7 +874,6 @@ void xs_suspend_cancel(void)
static int xenwatch_thread(void *unused)
{
struct list_head *ent;
struct xs_watch_event *event;
xenwatch_pid = current->pid;
@ -883,13 +888,15 @@ 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);
event = list_first_entry_or_null(&watch_events,
struct xs_watch_event, list);
if (event) {
list_del(&event->list);
event->handle->nr_pending--;
}
spin_unlock(&watch_events_lock);
if (ent != &watch_events) {
event = list_entry(ent, struct xs_watch_event, list);
if (event) {
event->handle->callback(event->handle, event->path,
event->token);
kfree(event);

2
include/xen/xenbus.h
View File

@ -61,6 +61,8 @@ 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.