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Re: [PATCH v5 1/2] vhost-user: fix VirtQ notifier cleanup
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH v5 1/2] vhost-user: fix VirtQ notifier cleanup |
Date: |
Tue, 19 Oct 2021 06:52:57 -0400 |
On Tue, Oct 19, 2021 at 03:57:42PM +0800, Xueming Li wrote:
> When vhost-user device cleanup and unmmap notifier address, VM cpu
you mean cleanup is executed and un-mmaps ...
> thread that writing the notifier failed
that writing -> writing
failed -> fails
> with accessing invalid address.
... error
>
> To avoid this concurrent issue, wait memory flatview update by draining
wait -> wait for a
> rcu callbacks, then unmap notifiers.
>
> Fixes: 44866521bd6e ("vhost-user: support registering external host
> notifiers")
> Cc: qemu-stable@nongnu.org
> Cc: Yuwei Zhang <zhangyuwei.9149@bytedance.com>
> Signed-off-by: Xueming Li <xuemingl@nvidia.com>
If I apply this, qos-test hangs.
> ---
> hw/virtio/vhost-user.c | 22 +++++++++++++++-------
> 1 file changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index bf6e50223c..cfca1b9adc 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -18,6 +18,7 @@
> #include "chardev/char-fe.h"
> #include "io/channel-socket.h"
> #include "sysemu/kvm.h"
> +#include "sysemu/cpus.h"
> #include "qemu/error-report.h"
> #include "qemu/main-loop.h"
> #include "qemu/sockets.h"
> @@ -1165,6 +1166,12 @@ static void vhost_user_host_notifier_remove(struct
> vhost_dev *dev,
>
> if (n->addr && n->set) {
> virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, false);
> + if (!qemu_in_vcpu_thread()) { /* Avoid vCPU dead lock. */
ok this avoids deadlock, but the comment does not explain:
why does not vcpu thread
need to wait for other VCPU threads? what if one of these
is in the middle of notify?
> + /* Wait for VM threads accessing old flatview which contains
> notifier. */
> + drain_call_rcu();
> + }
> + munmap(n->addr, qemu_real_host_page_size);
> + n->addr = NULL;
> n->set = false;
> }
> }
> @@ -1502,12 +1509,7 @@ static int
> vhost_user_slave_handle_vring_host_notifier(struct vhost_dev *dev,
>
> n = &user->notifier[queue_idx];
>
> - if (n->addr) {
> - virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, false);
> - object_unparent(OBJECT(&n->mr));
> - munmap(n->addr, page_size);
> - n->addr = NULL;
> - }
> + vhost_user_host_notifier_remove(dev, queue_idx);
>
> if (area->u64 & VHOST_USER_VRING_NOFD_MASK) {
> return 0;
> @@ -2485,11 +2487,17 @@ void vhost_user_cleanup(VhostUserState *user)
> for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
> if (user->notifier[i].addr) {
> object_unparent(OBJECT(&user->notifier[i].mr));
> + }
> + }
> + memory_region_transaction_commit();
> + /* Wait for VM threads accessing old flatview which contains notifier. */
> + drain_call_rcu();
> + for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
> + if (user->notifier[i].addr) {
> munmap(user->notifier[i].addr, qemu_real_host_page_size);
> user->notifier[i].addr = NULL;
> }
> }
> - memory_region_transaction_commit();
> user->chr = NULL;
> }
>
> --
> 2.33.0