During the process of hot-unplug in vhost-user-net NIC, vhost_user_cleanup may add same rcu node to rcu list. Function calls are as follows: vhost_user_cleanup ->vhost_user_host_notifier_remove ->call_rcu(n, vhost_user_host_notifier_free, rcu); ->g_free_rcu(n, rcu); When this happens, QEMU will abort in try_dequeue: if (head == &dummy && qatomic_mb_read(&tail) == &dummy.next) { abort(); } Backtrace is as follows: 0 __pthread_kill_implementation () at /usr/lib64/libc.so.6 1 raise () at /usr/lib64/libc.so.6 2 abort () at /usr/lib64/libc.so.6 3 try_dequeue () at ../util/rcu.c:235 4 call_rcu_thread (0) at ../util/rcu.c:288 5 qemu_thread_start (0) at ../util/qemu-thread-posix.c:541 6 start_thread () at /usr/lib64/libc.so.6 7 clone3 () at /usr/lib64/libc.so.6 Reason for the abort is that adding two identical nodes to the rcu list will cause it becomes a ring. After dummy node is added to the tail of the list in try_dequeue, the ring is opened. But lead to a situation that only one node is added to list and rcu_call_count is added twice. This will cause try_dequeue abort. This issue happens when n->addr != 0 in vhost_user_host_notifier_remove. It can happens in a hotplug stress test with a 32queue vhost-user-net type NIC. Because n->addr is set in VHOST_USER_BACKEND_VRING_HOST_NOTIFIER_MSG function. during device hotplug process and it is cleared in vhost_dev_stop during device hot-unplug. Since VHOST_USER_BACKEND_VRING_HOST_NOTIFIER_MSG is a message sent by DPDK to qemu, it is asynchronous. So, there is no guaranteed order between the two processes of setting n->addr and clearing n->addr. If setting n->addr in hotplug occurs after clearing n->addr in hotunplug, the issue will occur. So, it is necessary to merge g_free_rcu and vhost_user_host_notifier_free into one rcu node. Fixes: 503e355465 ("virtio/vhost-user: dynamically assign VhostUserHostNotifiers") Signed-off-by: yaozhenguo <yaozhenguo@jd.com> --- V1->V2: add n->addr check in vhost_user_get_vring_base and vhost_user_backend_handle_vring_host_notifier to prevent submit same node to rcu list. --- hw/virtio/vhost-user.c | 39 +++++++++++++++++++++------------------ include/hw/virtio/vhost-user.h | 1 + 2 files changed, 22 insertions(+), 18 deletions(-) diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index XXXXXXX..XXXXXXX 100644 --- a/hw/virtio/vhost-user.c +++ b/hw/virtio/vhost-user.c @@ -XXX,XX +XXX,XX @@ #else #define VHOST_USER_MAX_RAM_SLOTS 512 #endif - /* * Maximum size of virtio device config space */ @@ -XXX,XX +XXX,XX @@ static int vhost_user_set_vring_num(struct vhost_dev *dev, static void vhost_user_host_notifier_free(VhostUserHostNotifier *n) { - assert(n && n->unmap_addr); - munmap(n->unmap_addr, qemu_real_host_page_size()); - n->unmap_addr = NULL; + if (n->unmap_addr) { + munmap(n->unmap_addr, qemu_real_host_page_size()); + n->unmap_addr = NULL; + } + if (n->need_free) { + memory_region_transaction_begin(); + object_unparent(OBJECT(&n->mr)); + memory_region_transaction_commit(); + g_free(n); + } } /* @@ -XXX,XX +XXX,XX @@ static void vhost_user_host_notifier_free(VhostUserHostNotifier *n) * under rcu. */ static void vhost_user_host_notifier_remove(VhostUserHostNotifier *n, - VirtIODevice *vdev) + VirtIODevice *vdev, bool free) { if (n->addr) { if (vdev) { + memory_region_transaction_begin(); virtio_queue_set_host_notifier_mr(vdev, n->idx, &n->mr, false); + memory_region_transaction_commit(); } assert(!n->unmap_addr); n->unmap_addr = n->addr; n->addr = NULL; - call_rcu(n, vhost_user_host_notifier_free, rcu); } + n->need_free = free; + call_rcu(n, vhost_user_host_notifier_free, rcu); } static int vhost_user_set_vring_base(struct vhost_dev *dev, @@ -XXX,XX +XXX,XX @@ static int vhost_user_get_vring_base(struct vhost_dev *dev, struct vhost_user *u = dev->opaque; VhostUserHostNotifier *n = fetch_notifier(u->user, ring->index); - if (n) { - vhost_user_host_notifier_remove(n, dev->vdev); + if (n && n->addr) { + vhost_user_host_notifier_remove(n, dev->vdev, false); } ret = vhost_user_write(dev, &msg, NULL, 0); @@ -XXX,XX +XXX,XX @@ static int vhost_user_backend_handle_vring_host_notifier(struct vhost_dev *dev, * new mapped address. */ n = fetch_or_create_notifier(user, queue_idx); - vhost_user_host_notifier_remove(n, vdev); + if (n && n->addr) { + vhost_user_host_notifier_remove(n, vdev, false); + } if (area->u64 & VHOST_USER_VRING_NOFD_MASK) { return 0; @@ -XXX,XX +XXX,XX @@ static void vhost_user_state_destroy(gpointer data) { VhostUserHostNotifier *n = (VhostUserHostNotifier *) data; if (n) { - vhost_user_host_notifier_remove(n, NULL); - object_unparent(OBJECT(&n->mr)); - /* - * We can't free until vhost_user_host_notifier_remove has - * done it's thing so schedule the free with RCU. - */ - g_free_rcu(n, rcu); + vhost_user_host_notifier_remove(n, NULL, true); } } @@ -XXX,XX +XXX,XX @@ void vhost_user_cleanup(VhostUserState *user) if (!user->chr) { return; } - memory_region_transaction_begin(); user->notifiers = (GPtrArray *) g_ptr_array_free(user->notifiers, true); - memory_region_transaction_commit(); user->chr = NULL; } diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h index XXXXXXX..XXXXXXX 100644 --- a/include/hw/virtio/vhost-user.h +++ b/include/hw/virtio/vhost-user.h @@ -XXX,XX +XXX,XX @@ typedef struct VhostUserHostNotifier { void *addr; void *unmap_addr; int idx; + bool need_free; } VhostUserHostNotifier; /** -- 1.8.3.1 During the hot-unplugging of vhost-user-net type network cards, the vhost_user_cleanup function may add the same rcu node to the rcu linked list. The function call relationship in this case is as follows: vhost_user_cleanup ->vhost_user_host_notifier_remove ->call_rcu(n, vhost_user_host_notifier_free, rcu); ->g_free_rcu(n, rcu); When this happens, QEMU will abort in try_dequeue: if (head == &dummy && qatomic_mb_read(&tail) == &dummy.next) { abort(); } backtrace is as follows:: 0 __pthread_kill_implementation () at /usr/lib64/libc.so.6 1 raise () at /usr/lib64/libc.so.6 2 abort () at /usr/lib64/libc.so.6 3 try_dequeue () at ../util/rcu.c:235 4 call_rcu_thread (0) at ../util/rcu.c:288 5 qemu_thread_start (0) at ../util/qemu-thread-posix.c:541 6 start_thread () at /usr/lib64/libc.so.6 7 clone3 () at /usr/lib64/libc.so.6 The reason for the abort is that adding two identical nodes to the rcu linked list will cause the rcu linked list to become a ring, but when the dummy node is added after the two identical nodes, the ring is opened. But only one node is added to list with rcu_call_count added twice. This will cause rcu try_dequeue abort. This happens when n->addr != 0. In some scenarios, this does happen. For example, this situation will occur when using a 32-queue DPU vhost-user-net type network card for hot-unplug testing, because VhostUserHostNotifier->addr will be cleared during the processing of VHOST_USER_BACKEND_VRING_HOST_NOTIFIER_MSG. However,it is asynchronous, so we cannot guarantee that VhostUserHostNotifier->addr is zero in vhost_user_cleanup. Therefore, it is necessary to merge g_free_rcu and vhost_user_host_notifier_free into one rcu node. Fixes: 503e355465 ("virtio/vhost-user: dynamically assign VhostUserHostNotifiers") Signed-off-by: yaozhenguo <yaozhenguo@jd.com> --- V1->V2: add n->addr check in vhost_user_get_vring_base and vhost_user_backend_handle_vring_host_notifier to prevent submit same node to rcu list. V2->V3: 1. change "free" to "destroy" 2. move "!n->addr && !destroy" checking to vhost_user_host_notifier_remove 3. move "!n" checking to vhost_user_host_notifier_remove --- hw/virtio/vhost-user.c | 43 ++++++++++++++++++---------------- include/hw/virtio/vhost-user.h | 1 + 2 files changed, 24 insertions(+), 20 deletions(-) diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index XXXXXXX..XXXXXXX 100644 --- a/hw/virtio/vhost-user.c +++ b/hw/virtio/vhost-user.c @@ -XXX,XX +XXX,XX @@ static int vhost_user_set_vring_num(struct vhost_dev *dev, static void vhost_user_host_notifier_free(VhostUserHostNotifier *n) { - assert(n && n->unmap_addr); - munmap(n->unmap_addr, qemu_real_host_page_size()); - n->unmap_addr = NULL; + if (n->unmap_addr) { + munmap(n->unmap_addr, qemu_real_host_page_size()); + n->unmap_addr = NULL; + } + if (n->destroy) { + memory_region_transaction_begin(); + object_unparent(OBJECT(&n->mr)); + memory_region_transaction_commit(); + g_free(n); + } } /* @@ -XXX,XX +XXX,XX @@ static void vhost_user_host_notifier_free(VhostUserHostNotifier *n) * under rcu. */ static void vhost_user_host_notifier_remove(VhostUserHostNotifier *n, - VirtIODevice *vdev) + VirtIODevice *vdev, bool destroy) { + if (!n) + return; + if (!destroy && !n->addr) + return; + if (n->addr) { if (vdev) { + memory_region_transaction_begin(); virtio_queue_set_host_notifier_mr(vdev, n->idx, &n->mr, false); + memory_region_transaction_commit(); } assert(!n->unmap_addr); n->unmap_addr = n->addr; n->addr = NULL; - call_rcu(n, vhost_user_host_notifier_free, rcu); } + n->destroy = destroy; + call_rcu(n, vhost_user_host_notifier_free, rcu); } static int vhost_user_set_vring_base(struct vhost_dev *dev, @@ -XXX,XX +XXX,XX @@ static int vhost_user_get_vring_base(struct vhost_dev *dev, struct vhost_user *u = dev->opaque; VhostUserHostNotifier *n = fetch_notifier(u->user, ring->index); - if (n) { - vhost_user_host_notifier_remove(n, dev->vdev); - } + vhost_user_host_notifier_remove(n, dev->vdev, false); ret = vhost_user_write(dev, &msg, NULL, 0); if (ret < 0) { @@ -XXX,XX +XXX,XX @@ static int vhost_user_backend_handle_vring_host_notifier(struct vhost_dev *dev, * new mapped address. */ n = fetch_or_create_notifier(user, queue_idx); - vhost_user_host_notifier_remove(n, vdev); + vhost_user_host_notifier_remove(n, vdev, false); if (area->u64 & VHOST_USER_VRING_NOFD_MASK) { return 0; @@ -XXX,XX +XXX,XX @@ static int vhost_user_set_inflight_fd(struct vhost_dev *dev, static void vhost_user_state_destroy(gpointer data) { VhostUserHostNotifier *n = (VhostUserHostNotifier *) data; - if (n) { - vhost_user_host_notifier_remove(n, NULL); - object_unparent(OBJECT(&n->mr)); - /* - * We can't free until vhost_user_host_notifier_remove has - * done it's thing so schedule the free with RCU. - */ - g_free_rcu(n, rcu); - } + vhost_user_host_notifier_remove(n, NULL, true); } bool vhost_user_init(VhostUserState *user, CharBackend *chr, Error **errp) @@ -XXX,XX +XXX,XX @@ void vhost_user_cleanup(VhostUserState *user) if (!user->chr) { return; } - memory_region_transaction_begin(); user->notifiers = (GPtrArray *) g_ptr_array_free(user->notifiers, true); - memory_region_transaction_commit(); user->chr = NULL; } diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h index XXXXXXX..XXXXXXX 100644 --- a/include/hw/virtio/vhost-user.h +++ b/include/hw/virtio/vhost-user.h @@ -XXX,XX +XXX,XX @@ typedef struct VhostUserHostNotifier { void *addr; void *unmap_addr; int idx; + bool destroy; } VhostUserHostNotifier; /** -- 2.41.0