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Date: Thu, 30 May 2024 17:57:31 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: Jason Wang <jasowang@...hat.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Jiri Pirko <jiri@...nulli.us>,
Daniel Jurgens <danielj@...dia.com>,
netdev@...r.kernel.org,
virtualization@...ts.linux.dev
Subject: Re: [PATCH net v3 2/2] virtio_net: fix a spurious deadlock issue
On Tue, 28 May 2024 21:41:16 +0800, Heng Qi <hengqi@...ux.alibaba.com> wrote:
> When the following snippet is run, lockdep will report a deadlock[1].
>
> /* Acquire all queues dim_locks */
> for (i = 0; i < vi->max_queue_pairs; i++)
> mutex_lock(&vi->rq[i].dim_lock);
>
> There's no deadlock here because the vq locks are always taken
> in the same order, but lockdep can not figure it out. So refactoring
> the code to alleviate the problem.
>
> [1]
> ========================================================
> WARNING: possible recursive locking detected
> 6.9.0-rc7+ #319 Not tainted
> --------------------------------------------
> ethtool/962 is trying to acquire lock:
>
> but task is already holding lock:
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(&vi->rq[i].dim_lock);
> lock(&vi->rq[i].dim_lock);
>
> *** DEADLOCK ***
>
> May be due to missing lock nesting notation
>
> 3 locks held by ethtool/962:
> #0: ffffffff82dbaab0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x19/0x40
> #1: ffffffff82dad0a8 (rtnl_mutex){+.+.}-{3:3}, at:
> ethnl_default_set_doit+0xbe/0x1e0
>
> stack backtrace:
> CPU: 6 PID: 962 Comm: ethtool Not tainted 6.9.0-rc7+ #319
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> Call Trace:
> <TASK>
> dump_stack_lvl+0x79/0xb0
> check_deadlock+0x130/0x220
> __lock_acquire+0x861/0x990
> lock_acquire.part.0+0x72/0x1d0
> ? lock_acquire+0xf8/0x130
> __mutex_lock+0x71/0xd50
> virtnet_set_coalesce+0x151/0x190
> __ethnl_set_coalesce.isra.0+0x3f8/0x4d0
> ethnl_set_coalesce+0x34/0x90
> ethnl_default_set_doit+0xdd/0x1e0
> genl_family_rcv_msg_doit+0xdc/0x130
> genl_family_rcv_msg+0x154/0x230
> ? __pfx_ethnl_default_set_doit+0x10/0x10
> genl_rcv_msg+0x4b/0xa0
> ? __pfx_genl_rcv_msg+0x10/0x10
> netlink_rcv_skb+0x5a/0x110
> genl_rcv+0x28/0x40
> netlink_unicast+0x1af/0x280
> netlink_sendmsg+0x20e/0x460
> __sys_sendto+0x1fe/0x210
> ? find_held_lock+0x2b/0x80
> ? do_user_addr_fault+0x3a2/0x8a0
> ? __lock_release+0x5e/0x160
> ? do_user_addr_fault+0x3a2/0x8a0
> ? lock_release+0x72/0x140
> ? do_user_addr_fault+0x3a7/0x8a0
> __x64_sys_sendto+0x29/0x30
> do_syscall_64+0x78/0x180
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> Fixes: 4d4ac2ececd3 ("virtio_net: Add a lock for per queue RX coalesce")
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> drivers/net/virtio_net.c | 36 ++++++++++++++++--------------------
> 1 file changed, 16 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 4f828a9e5889..ecb5203d0372 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -4257,7 +4257,6 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
> struct virtio_net_ctrl_coal_rx *coal_rx __free(kfree) = NULL;
> bool rx_ctrl_dim_on = !!ec->use_adaptive_rx_coalesce;
> struct scatterlist sgs_rx;
> - int ret = 0;
> int i;
>
> if (rx_ctrl_dim_on && !virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
> @@ -4267,27 +4266,27 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
> ec->rx_max_coalesced_frames != vi->intr_coal_rx.max_packets))
> return -EINVAL;
>
> - /* Acquire all queues dim_locks */
> - for (i = 0; i < vi->max_queue_pairs; i++)
> - mutex_lock(&vi->rq[i].dim_lock);
> -
> if (rx_ctrl_dim_on && !vi->rx_dim_enabled) {
> vi->rx_dim_enabled = true;
> - for (i = 0; i < vi->max_queue_pairs; i++)
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> + mutex_lock(&vi->rq[i].dim_lock);
> vi->rq[i].dim_enabled = true;
> - goto unlock;
> + mutex_unlock(&vi->rq[i].dim_lock);
> + }
> + return 0;
> }
>
> coal_rx = kzalloc(sizeof(*coal_rx), GFP_KERNEL);
> - if (!coal_rx) {
> - ret = -ENOMEM;
> - goto unlock;
> - }
> + if (!coal_rx)
> + return -ENOMEM;
>
> if (!rx_ctrl_dim_on && vi->rx_dim_enabled) {
> vi->rx_dim_enabled = false;
> - for (i = 0; i < vi->max_queue_pairs; i++)
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> + mutex_lock(&vi->rq[i].dim_lock);
> vi->rq[i].dim_enabled = false;
> + mutex_unlock(&vi->rq[i].dim_lock);
> + }
> }
>
> /* Since the per-queue coalescing params can be set,
> @@ -4300,22 +4299,19 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
>
> if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_NOTF_COAL,
> VIRTIO_NET_CTRL_NOTF_COAL_RX_SET,
> - &sgs_rx)) {
> - ret = -EINVAL;
> - goto unlock;
> - }
> + &sgs_rx))
> + return -EINVAL;
>
> vi->intr_coal_rx.max_usecs = ec->rx_coalesce_usecs;
> vi->intr_coal_rx.max_packets = ec->rx_max_coalesced_frames;
> for (i = 0; i < vi->max_queue_pairs; i++) {
> + mutex_lock(&vi->rq[i].dim_lock);
> vi->rq[i].intr_coal.max_usecs = ec->rx_coalesce_usecs;
> vi->rq[i].intr_coal.max_packets = ec->rx_max_coalesced_frames;
> - }
> -unlock:
> - for (i = vi->max_queue_pairs - 1; i >= 0; i--)
> mutex_unlock(&vi->rq[i].dim_lock);
> + }
>
> - return ret;
> + return 0;
> }
>
> static int virtnet_send_notf_coal_cmds(struct virtnet_info *vi,
> --
> 2.32.0.3.g01195cf9f
>
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