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Commit df3367c1 authored by SeongJae Park's avatar SeongJae Park Committed by Greg Kroah-Hartman
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xen/xenbus: Count pending messages for each watch 



commit 3dc86ca6b4c8cfcba9da7996189d1b5a358a94fc upstream.

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>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 19cfeffc

drivers/xen/xenbus/xenbus_xs.c

+19 −12
Original line number Diff line number Diff line
@@ -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);
@@ -750,6 +752,7 @@ 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(msg, tmp, &watch_events, list) {

			if (msg->u.watch.handle != watch)

				continue;
@@ -757,6 +760,8 @@ void unregister_xenbus_watch(struct xenbus_watch *watch) 
			kfree(msg->u.watch.vec);

			kfree(msg);

		}

		watch->nr_pending = 0;

	}

	spin_unlock(&watch_events_lock);



	if (current->pid != xenwatch_pid)
@@ -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,
@@ -911,6 +917,7 @@ static int process_msg(void) 
					 msg->u.watch.vec_size))) {

			spin_lock(&watch_events_lock);

			list_add_tail(&msg->list, &watch_events);

			msg->u.watch.handle->nr_pending++;

			wake_up(&watch_events_waitq);

			spin_unlock(&watch_events_lock);

		} else {

include/xen/xenbus.h

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