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To: Patrick Fu <patrick.fu@intel.com>, dev@dpdk.org, chenbo.xia@intel.com
Cc: zhihong.wang@intel.com, cheng1.jiang@intel.com
References: <20200911015316.1903181-1-patrick.fu@intel.com>
<20201013014546.2896162-1-patrick.fu@intel.com>
<20201013014546.2896162-5-patrick.fu@intel.com>
From: Maxime Coquelin <maxime.coquelin@redhat.com>
Message-ID: <356521e5-d987-1973-c252-691867ca4bf0@redhat.com>
Date: Wed, 14 Oct 2020 11:34:54 +0200
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Subject: Re: [dpdk-dev] [PATCH v4 4/4] vhost: fix async unregister deadlock
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On 10/13/20 3:45 AM, Patrick Fu wrote:
> When async unregister function is invoked in certain vhost event
> callbacks (e.g. vring state change), deadlock may occur due to
> recursive spinlock acquire. This patch uses trylock() primitive in
> the unregister API to avoid deadlock.
>
> Fixes: 78639d54563a ("vhost: introduce async enqueue registration API")
>
> Signed-off-by: Patrick Fu <patrick.fu@intel.com>
> ---
> lib/librte_vhost/vhost.c | 9 +++++++--
> lib/librte_vhost/vhost_user.c | 4 ++--
> 2 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index 323565898..6068c38ec 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -1633,10 +1633,15 @@ int rte_vhost_async_channel_unregister(int vid, uint16_t queue_id)
> return ret;
>
> ret = 0;
> - rte_spinlock_lock(&vq->access_lock);
>
> if (!vq->async_registered)
> - goto out;
> + return ret;
> +
> + if (!rte_spinlock_trylock(&vq->access_lock)) {
> + VHOST_LOG_CONFIG(ERR, "Failed to unregister async channel. "
> + "virt queue busy.\n");
> + return -1;
> + }
>
> if (vq->async_pkts_inflight_n) {
> VHOST_LOG_CONFIG(ERR, "Failed to unregister async channel. "
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index 1656ec736..d20c8c57a 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -1980,9 +1980,9 @@ vhost_user_set_vring_enable(struct virtio_net **pdev,
> "set queue enable: %d to qp idx: %d\n",
> enable, index);
>
> - if (!enable && dev->virtqueue[index]->async_registered) {
> + if (enable && dev->virtqueue[index]->async_registered) {
> if (dev->virtqueue[index]->async_pkts_inflight_n) {
> - VHOST_LOG_CONFIG(ERR, "failed to disable vring. "
> + VHOST_LOG_CONFIG(ERR, "failed to enable vring. "
> "async inflight packets must be completed first\n");
> return RTE_VHOST_MSG_RESULT_ERR;
> }
>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Thanks,
Maxime