From patchwork Thu Jul 2 15:38:11 2009 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Gregory Haskins X-Patchwork-Id: 33716 Received: from vger.kernel.org (vger.kernel.org [209.132.176.167]) by demeter.kernel.org (8.14.2/8.14.2) with ESMTP id n62FeZQl017615 for ; Thu, 2 Jul 2009 15:40:35 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754636AbZGBPiY (ORCPT ); Thu, 2 Jul 2009 11:38:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755071AbZGBPiY (ORCPT ); Thu, 2 Jul 2009 11:38:24 -0400 Received: from victor.provo.novell.com ([137.65.250.26]:46664 "EHLO victor.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755409AbZGBPiV (ORCPT ); Thu, 2 Jul 2009 11:38:21 -0400 Received: from dev.haskins.net (prv-ext-foundry1.gns.novell.com [137.65.251.240]) by victor.provo.novell.com with ESMTP (TLS encrypted); Thu, 02 Jul 2009 09:38:13 -0600 Received: from dev.haskins.net (localhost [127.0.0.1]) by dev.haskins.net (Postfix) with ESMTP id 84678464233; Thu, 2 Jul 2009 11:38:11 -0400 (EDT) From: Gregory Haskins Subject: [KVM PATCH v9 3/5] KVM: Fix races in irqfd using new eventfd_kref_get interface To: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, mst@redhat.com, avi@redhat.com, davidel@xmailserver.org Date: Thu, 02 Jul 2009 11:38:11 -0400 Message-ID: <20090702153811.20186.994.stgit@dev.haskins.net> In-Reply-To: <20090702153454.20186.99191.stgit@dev.haskins.net> References: <20090702153454.20186.99191.stgit@dev.haskins.net> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org eventfd currently emits a POLLHUP wakeup on f_ops->release() to generate a "release" callback. This lets eventfd clients know if the eventfd is about to go away and is very useful particularly for in-kernel clients. However, until recently it is not possible to use this feature of eventfd in a race-free way. This patch utilizes a new eventfd interface to rectify the problem. It also carefully coordinates the shutdown path using a deferred work-item so that we may support a full mutual-disassociate protocol between KVM and eventfd. Signed-off-by: Gregory Haskins --- include/linux/kvm_host.h | 5 + virt/kvm/eventfd.c | 158 ++++++++++++++++++++++++++++++++++++++-------- 2 files changed, 136 insertions(+), 27 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 9634f31..8e04a34 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -146,7 +146,10 @@ struct kvm { struct kvm_io_bus mmio_bus; struct kvm_io_bus pio_bus; #ifdef CONFIG_HAVE_KVM_EVENTFD - struct list_head irqfds; + struct { + spinlock_t lock; + struct list_head items; + } irqfds; #endif struct kvm_vm_stat stat; struct kvm_arch arch; diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index 9656027..9da9286 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -36,16 +36,21 @@ * Credit goes to Avi Kivity for the original idea. * -------------------------------------------------------------------- */ + struct _irqfd { struct kvm *kvm; + struct eventfd_ctx *eventfd; int gsi; struct list_head list; poll_table pt; wait_queue_head_t *wqh; wait_queue_t wait; struct work_struct inject; + struct work_struct shutdown; }; +static struct workqueue_struct *irqfd_cleanup_wq; + static void irqfd_inject(struct work_struct *work) { @@ -58,30 +63,89 @@ irqfd_inject(struct work_struct *work) mutex_unlock(&kvm->irq_lock); } +/* + * Race-free decouple logic (ordering is critical) + */ +static void +irqfd_shutdown(struct work_struct *work) +{ + struct _irqfd *irqfd = container_of(work, struct _irqfd, shutdown); + + /* + * Synchronize with the wait-queue and unhook ourselves to prevent + * further events. + */ + remove_wait_queue(irqfd->wqh, &irqfd->wait); + + /* + * We know no new events will be scheduled at this point, so block + * until all previously outstanding events have completed + */ + flush_work(&irqfd->inject); + + /* + * It is now safe to release the object's resources + */ + eventfd_ctx_put(irqfd->eventfd); + kfree(irqfd); +} + + +/* assumes kvm->irqfds.lock is held */ +static bool +irqfd_is_active(struct _irqfd *irqfd) +{ + return list_empty(&irqfd->list) ? false : true; +} + +/* + * Mark the irqfd as inactive and schedule it for removal + * + * assumes kvm->irqfds.lock is held + */ +static void +irqfd_deactivate(struct _irqfd *irqfd) +{ + BUG_ON(!irqfd_is_active(irqfd)); + + list_del_init(&irqfd->list); + + queue_work(irqfd_cleanup_wq, &irqfd->shutdown); +} + +/* + * Called with wqh->lock held and interrupts disabled + */ static int irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key) { struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait); unsigned long flags = (unsigned long)key; - /* - * Assume we will be called with interrupts disabled - */ if (flags & POLLIN) - /* - * Defer the IRQ injection until later since we need to - * acquire the kvm->lock to do so. - */ + /* An event has been signaled, inject an interrupt */ schedule_work(&irqfd->inject); if (flags & POLLHUP) { + /* The eventfd is closing, detach from KVM */ + struct kvm *kvm = irqfd->kvm; + unsigned long flags; + + spin_lock_irqsave(&kvm->irqfds.lock, flags); + /* - * for now, just remove ourselves from the list and let - * the rest dangle. We will fix this up later once - * the races in eventfd are fixed + * We must check if someone deactivated the irqfd before + * we could acquire the irqfds.lock since the item is + * deactivated from the KVM side before it is unhooked from + * the wait-queue. If it is already deactivated, we can + * simply return knowing the other side will cleanup for us. + * We cannot race against the irqfd going away since the + * other side is required to acquire wqh->lock, which we hold */ - __remove_wait_queue(irqfd->wqh, &irqfd->wait); - irqfd->wqh = NULL; + if (irqfd_is_active(irqfd)) + irqfd_deactivate(irqfd); + + spin_unlock_irqrestore(&kvm->irqfds.lock, flags); } return 0; @@ -102,6 +166,7 @@ kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags) { struct _irqfd *irqfd; struct file *file = NULL; + struct eventfd_ctx *eventfd = NULL; int ret; unsigned int events; @@ -113,6 +178,7 @@ kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags) irqfd->gsi = gsi; INIT_LIST_HEAD(&irqfd->list); INIT_WORK(&irqfd->inject, irqfd_inject); + INIT_WORK(&irqfd->shutdown, irqfd_shutdown); file = eventfd_fget(fd); if (IS_ERR(file)) { @@ -120,6 +186,14 @@ kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags) goto fail; } + eventfd = eventfd_ctx_fileget(file); + if (IS_ERR(eventfd)) { + ret = PTR_ERR(eventfd); + goto fail; + } + + irqfd->eventfd = eventfd; + /* * Install our own custom wake-up handling so we are notified via * a callback whenever someone signals the underlying eventfd @@ -129,12 +203,13 @@ kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags) events = file->f_op->poll(file, &irqfd->pt); - mutex_lock(&kvm->lock); - list_add_tail(&irqfd->list, &kvm->irqfds); - mutex_unlock(&kvm->lock); + spin_lock_irq(&kvm->irqfds.lock); + list_add_tail(&irqfd->list, &kvm->irqfds.items); + spin_unlock_irq(&kvm->irqfds.lock); /* - * Check if there was an event already queued + * Check if there was an event already pending on the eventfd + * before we registered, and trigger it as if we didn't miss it. */ if (events & POLLIN) schedule_work(&irqfd->inject); @@ -148,6 +223,9 @@ kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags) return 0; fail: + if (eventfd && !IS_ERR(eventfd)) + eventfd_ctx_put(eventfd); + if (file && !IS_ERR(file)) fput(file); @@ -158,24 +236,52 @@ fail: void kvm_irqfd_init(struct kvm *kvm) { - INIT_LIST_HEAD(&kvm->irqfds); + spin_lock_init(&kvm->irqfds.lock); + INIT_LIST_HEAD(&kvm->irqfds.items); } +/* + * This function is called as the kvm VM fd is being released. Shutdown all + * irqfds that still remain open + */ void kvm_irqfd_release(struct kvm *kvm) { struct _irqfd *irqfd, *tmp; - list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds, list) { - if (irqfd->wqh) - remove_wait_queue(irqfd->wqh, &irqfd->wait); + spin_lock_irq(&kvm->irqfds.lock); - flush_work(&irqfd->inject); + list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) + irqfd_deactivate(irqfd); - mutex_lock(&kvm->lock); - list_del(&irqfd->list); - mutex_unlock(&kvm->lock); + spin_unlock_irq(&kvm->irqfds.lock); + + /* + * Block until we know all outstanding shutdown jobs have completed + * since we do not take a kvm* reference. + */ + flush_workqueue(irqfd_cleanup_wq); - kfree(irqfd); - } } + +/* + * create a host-wide workqueue for issuing deferred shutdown requests + * aggregated from all vm* instances. We need our own isolated single-thread + * queue to prevent deadlock against flushing the normal work-queue. + */ +static int __init irqfd_module_init(void) +{ + irqfd_cleanup_wq = create_singlethread_workqueue("kvm-irqfd-cleanup"); + if (!irqfd_cleanup_wq) + return -ENOMEM; + + return 0; +} + +static void __exit irqfd_module_exit(void) +{ + destroy_workqueue(irqfd_cleanup_wq); +} + +module_init(irqfd_module_init); +module_exit(irqfd_module_exit);