Re: [PATCH 4/5] xen/xenbus: Count pending messages for each watch

On 17.12.20 09:17, SeongJae Park wrote:

From: SeongJae Park sjpark@amazon.de

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@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 Signed-off-by: Author Redacted security@xen.org Reviewed-by: Juergen Gross jgross@suse.com Signed-off-by: Juergen Gross jgross@suse.com

---

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;

I'm missing the incrementing of nr_pending, which was present in the upstream patch.

Juergen

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.