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Message-Id: <20201228124852.693932549@linuxfoundation.org>
Date: Mon, 28 Dec 2020 13:50:14 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, SeongJae Park <sjpark@...zon.de>,
Michael Kurth <mku@...zon.de>,
Pawel Wieczorkiewicz <wipawel@...zon.de>,
Juergen Gross <jgross@...e.com>
Subject: [PATCH 4.4 130/132] xen/xenbus: Count pending messages for each watch
From: SeongJae Park <sjpark@...zon.de>
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@...r.kernel.org
Signed-off-by: SeongJae Park <sjpark@...zon.de>
Reported-by: Michael Kurth <mku@...zon.de>
Reported-by: Pawel Wieczorkiewicz <wipawel@...zon.de>
Reviewed-by: Juergen Gross <jgross@...e.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
drivers/xen/xenbus/xenbus_xs.c | 31 +++++++++++++++++++------------
include/xen/xenbus.h | 2 ++
2 files changed, 21 insertions(+), 12 deletions(-)
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -701,6 +701,8 @@ int register_xenbus_watch(struct xenbus_
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 xenb
/* 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,
@@ -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 {
--- 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.
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