Commit 3dc86ca6 authored by SeongJae Park's avatar SeongJae Park Committed by Juergen Gross
Browse files

xen/xenbus: Count pending messages for each watch 



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: default avatarSeongJae Park <sjpark@amazon.de>
Reported-by: default avatarMichael Kurth <mku@amazon.de>
Reported-by: default avatarPawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent be987200

drivers/xen/xenbus/xenbus_xs.c

+18 −11
Original line number Diff line number Diff line
@@ -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);

include/xen/xenbus.h

+2 −0
Original line number Diff line number Diff line
@@ -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.

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