| Message ID | 20240913080800.40816-1-yaozhenguo@jd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V1] virtio/vhost-user: fix qemu abort when hotunplug vhost-user-net device | expand |
yaozhenguo <yaozhenguo1@gmail.com> 于2024年9月13日周五 16:08写道： > > 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> > --- > hw/virtio/vhost-user.c | 34 ++++++++++++++++++---------------- > include/hw/virtio/vhost-user.h | 1 + > 2 files changed, 19 insertions(+), 16 deletions(-) > > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c > index 00561da..b2da3cf 100644 > --- a/hw/virtio/vhost-user.c > +++ b/hw/virtio/vhost-user.c > @@ -1185,9 +1185,16 @@ 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); > + } > } > > /* > @@ -1195,17 +1202,20 @@ 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); > } This brings up another problem. When the device is initialized, problems may occur when the execution times of vhost_user_get_vring_base and vhost_user_backend_handle_vring_host_notifier are relatively close, and the same node is submitted to the rcu list. This happened during our regression testing. Therefore, modifications must be made to avoid this problem. vhost_user_get_vring_base vhost_user_host_notifier_remove(n, dev->vdev, false); vhost_user_backend_handle_vring_host_notifier vhost_user_host_notifier_remove(n, dev->vdev, false); > > static int vhost_user_set_vring_base(struct vhost_dev *dev, > @@ -1280,7 +1290,7 @@ static int vhost_user_get_vring_base(struct vhost_dev *dev, > > 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); > @@ -1562,7 +1572,7 @@ 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; > @@ -2737,13 +2747,7 @@ 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); > } > } > > @@ -2765,9 +2769,7 @@ 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 324cd86..a171f29 100644 > --- a/include/hw/virtio/vhost-user.h > +++ b/include/hw/virtio/vhost-user.h > @@ -54,6 +54,7 @@ typedef struct VhostUserHostNotifier { > void *addr; > void *unmap_addr; > int idx; > + bool need_free; > } VhostUserHostNotifier; > > /** > -- > 1.8.3.1 >
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index 00561da..b2da3cf 100644 --- a/hw/virtio/vhost-user.c +++ b/hw/virtio/vhost-user.c @@ -1185,9 +1185,16 @@ 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); + } } /* @@ -1195,17 +1202,20 @@ 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, @@ -1280,7 +1290,7 @@ static int vhost_user_get_vring_base(struct vhost_dev *dev, 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); @@ -1562,7 +1572,7 @@ 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; @@ -2737,13 +2747,7 @@ 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); } } @@ -2765,9 +2769,7 @@ 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 324cd86..a171f29 100644 --- a/include/hw/virtio/vhost-user.h +++ b/include/hw/virtio/vhost-user.h @@ -54,6 +54,7 @@ typedef struct VhostUserHostNotifier { void *addr; void *unmap_addr; int idx; + bool need_free; } VhostUserHostNotifier; /**
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> --- hw/virtio/vhost-user.c | 34 ++++++++++++++++++---------------- include/hw/virtio/vhost-user.h | 1 + 2 files changed, 19 insertions(+), 16 deletions(-)