Messages in this thread | | | Subject | Re: [Xen-devel] [PATCH 2/6] xenbus: implement the xenwatch multithreading framework | From | Dongli Zhang <> | Date | Mon, 17 Sep 2018 09:48:44 +0800 |
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Hi Boris,
On 09/17/2018 05:20 AM, Boris Ostrovsky wrote: > > > On 9/14/18 3:34 AM, Dongli Zhang wrote: >> >> + >> +/* Running in the context of default xenwatch kthread. */ >> +void mtwatch_create_domain(domid_t domid) >> +{ >> + struct mtwatch_domain *domain; >> + >> + if (!domid) { >> + pr_err("Default xenwatch thread is for dom0\n"); >> + return; >> + } >> + >> + spin_lock(&mtwatch_info->domain_lock); >> + >> + domain = mtwatch_find_domain(domid); >> + if (domain) { >> + atomic_inc(&domain->refcnt); >> + spin_unlock(&mtwatch_info->domain_lock); >> + return; >> + } >> + >> + domain = kzalloc(sizeof(*domain), GFP_ATOMIC); > > Is there a reason (besides this being done under spinlock) for using GFP_ATOMIC? > If domain_lock is the only reason I'd probably drop the lock and do GFP_KERNEL.
spin_lock is the reason.
Would you like to switch to a mutex here?
> > >> + if (!domain) { >> + spin_unlock(&mtwatch_info->domain_lock); >> + pr_err("Failed to allocate memory for mtwatch thread %d\n", >> + domid); >> + return; > > This needs to return an error code, I think. Or do you want to fall back to > shared xenwatch thread?
We would fall back to the shared default xenwatch thread. As in [PATCH 3/6], the event is dispatched to the shared xenwatch thread if the per-domU one is not available.
> > >> + } >> + >> + domain->domid = domid; >> + atomic_set(&domain->refcnt, 1); >> + mutex_init(&domain->domain_mutex); >> + INIT_LIST_HEAD(&domain->purge_node); >> + >> + init_waitqueue_head(&domain->events_wq); >> + spin_lock_init(&domain->events_lock); >> + INIT_LIST_HEAD(&domain->events); >> + >> + list_add_tail_rcu(&domain->list_node, &mtwatch_info->domain_list); >> + >> + hlist_add_head_rcu(&domain->hash_node, >> + &mtwatch_info->domain_hash[MTWATCH_HASH(domid)]); >> + >> + spin_unlock(&mtwatch_info->domain_lock); >> + >> + domain->task = kthread_run(mtwatch_thread, domain, >> + "xen-mtwatch-%d", domid); >> + >> + if (!domain->task) { >> + pr_err("mtwatch kthread creation is failed\n"); >> + domain->state = MTWATCH_DOMAIN_DOWN; > > > Why not clean up right here?
I used to think there might be a race between mtwatch_create_domain() and mtwatch_put_domain().
Just realized the race is impossible. I will clean up here.
> >> + >> + return; >> + } >> + >> + domain->state = MTWATCH_DOMAIN_UP; >> +} >> + > > >> + >> void unregister_xenbus_watch(struct xenbus_watch *watch) >> { >> struct xs_watch_event *event, *tmp; >> @@ -831,6 +1100,9 @@ void unregister_xenbus_watch(struct xenbus_watch *watch) >> if (current->pid != xenwatch_pid) >> mutex_unlock(&xenwatch_mutex); >> + >> + if (xen_mtwatch && watch->get_domid) >> + unregister_mtwatch(watch); > > > I may not be understanding the logic flow here, but if we successfully > removed/unregistered/purged the watch from mtwatch lists, do we still need to > try removing it from watch_events list below?
Part of original unregister_xenbus_watch() has already removed the pending events from watch_events before the above added lines of code.
Dongli Zhang
> > > -boris > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xenproject.org > https://lists.xenproject.org/mailman/listinfo/xen-devel
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