hw/virtio/vhost-user.c | 39 +++++++++++++++++++++------------------ include/hw/virtio/vhost-user.h | 1 + 2 files changed, 22 insertions(+), 18 deletions(-)
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 00561da..ba4c09c 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -51,7 +51,6 @@
#else
#define VHOST_USER_MAX_RAM_SLOTS 512
#endif
-
/*
* Maximum size of virtio device config space
*/
@@ -1185,9 +1184,16 @@ 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 +1201,20 @@ 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,
@@ -1279,8 +1288,8 @@ 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);
@@ -1562,7 +1571,9 @@ 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;
@@ -2737,13 +2748,7 @@ 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 +2770,7 @@ 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;
/**
--
1.8.3.1On Thu, Sep 19, 2024 at 03:29:44PM GMT, yaozhenguo wrote:
>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 00561da..ba4c09c 100644
>--- a/hw/virtio/vhost-user.c
>+++ b/hw/virtio/vhost-user.c
>@@ -51,7 +51,6 @@
> #else
> #define VHOST_USER_MAX_RAM_SLOTS 512
> #endif
>-
> /*
> * Maximum size of virtio device config space
> */
>@@ -1185,9 +1184,16 @@ 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 +1201,20 @@ 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)
What about `destroy` instead of `free`?
In that way is more clear that it should be true when called by
`vhost_user_state_destroy()`.
> {
> 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);
> }
Instead of checking n->addr in the caller, I suggest to move the check
here:
if (destroy || n->unmap_addr) {
s->destroy = destroy;
call_rcu(n, vhost_user_host_notifier_free, rcu);
}
Thanks,
Stefano
>+ n->need_free = free;
>+ call_rcu(n, vhost_user_host_notifier_free, rcu);
> }
>
> static int vhost_user_set_vring_base(struct vhost_dev *dev,
>@@ -1279,8 +1288,8 @@ 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);
>@@ -1562,7 +1571,9 @@ 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;
>@@ -2737,13 +2748,7 @@ 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 +2770,7 @@ 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
>
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