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References: <20241118162424.9038-1-stephen@networkplumber.org>
In-Reply-To: <20241118162424.9038-1-stephen@networkplumber.org>
From: David Marchand <david.marchand@redhat.com>
Date: Mon, 25 Nov 2024 12:14:35 +0100
Message-ID: <CAJFAV8z0KnemZs8VNZisFt=RvK5Xx61Q9RUSk+Mv4aXoRxi3Zw@mail.gmail.com>
Subject: Re: [PATCH] vhost: fix read vs write lock mismatch
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: dev@dpdk.org, stable@dpdk.org,
Maxime Coquelin <maxime.coquelin@redhat.com>, Chenbo Xia <chenbox@nvidia.com>,
Eelco Chaudron <echaudro@redhat.com>
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On Mon, Nov 18, 2024 at 5:24=E2=80=AFPM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> If lock is acquired for write, it must be released for write
> or a deadlock is likely.
>
> Bugzilla ID: 1582
> Fixes: 9fc93a1e2320 ("vhost: fix virtqueue access check in datapath")
> Cc: david.marchand@redhat.com
> Cc: stable@dpdk.org
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> lib/vhost/virtio_net.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 298a5dae74..d764d4bc6a 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -2538,7 +2538,7 @@ virtio_dev_rx_async_submit(struct virtio_net *dev, =
struct vhost_virtqueue *vq,
>
> if (unlikely(!vq->access_ok)) {
> vhost_user_iotlb_rd_unlock(vq);
> - rte_rwlock_read_unlock(&vq->access_lock);
> + rte_rwlock_write_unlock(&vq->access_lock);
A write lock is taken earlier, because virtio_dev_rx_async_submit_*
need it for access to vq->async (as opposed to the sync code that only
takes read lock).
Here, no need to release/take again all locks.
A simpler fix is to directly call vring_translate(dev, vq).
--=20
David Marchand