From: SeongJae Park sjpark@amazon.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@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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.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 @@ -699,6 +699,8 @@ 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); @@ -748,12 +750,15 @@ 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);
@@ -800,7 +805,6 @@ void xs_suspend_cancel(void)
static int xenwatch_thread(void *unused) { - struct list_head *ent; struct xs_stored_msg *msg;
for (;;) { @@ -813,13 +817,15 @@ 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, @@ -909,6 +915,7 @@ 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.