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Date: Wed, 22 May 2024 16:52:19 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: netdev@...r.kernel.org,
virtualization@...ts.linux.dev,
Jason Wang <jasowang@...hat.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net 2/2] Revert "virtio_net: Add a lock for per queue RX coalesce"
On Wed, 22 May 2024 10:15:46 +0200, Jiri Pirko <jiri@...nulli.us> wrote:
> Wed, May 22, 2024 at 05:45:48AM CEST, hengqi@...ux.alibaba.com wrote:
> >This reverts commit 4d4ac2ececd3c42a08dd32a6e3a4aaf25f7efe44.
>
> This commit does not exist in -net or -net-next.
It definitely exists in net-next :):
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=4d4ac2ececd3c42a08dd32a6e3a4aaf25f7efe44
>
> >
> >When the following snippet is run, lockdep will complain[1].
> >
> > /* Acquire all queues dim_locks */
> > for (i = 0; i < vi->max_queue_pairs; i++)
> > mutex_lock(&vi->rq[i].dim_lock);
> >
> >At the same time, too many queues will cause lockdep to be more irritable,
> >which can be alleviated by using mutex_lock_nested(), however, there are
> >still new warning when the number of queues exceeds MAX_LOCKDEP_SUBCLASSES.
> >So I would like to gently revert this commit, although it brings
> >unsynchronization that is not so concerned:
> > 1. When dim is enabled, rx_dim_work may modify the coalescing parameters.
> > Users may read dirty coalescing parameters if querying.
> > 2. When dim is switched from enabled to disabled, a spurious dim worker
> > maybe scheduled, but this can be handled correctly by rx_dim_work.
> >
> >[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
> >
> >Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
>
> Fixes tag missing.
IIUC,
"This reverts commit 4d4ac2ececd3c42a08dd32a6e3a4aaf25f7efe44."
has provided a traceback way, which is not fixing other patches,
but fixing itself. So we do not need fixes tag.
Thanks.
>
>
> >---
> > drivers/net/virtio_net.c | 53 +++++++++-------------------------------
> > 1 file changed, 12 insertions(+), 41 deletions(-)
> >
> >diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> >index 1cad06cef230..e4a1dff2a64a 100644
> >--- a/drivers/net/virtio_net.c
> >+++ b/drivers/net/virtio_net.c
> >@@ -316,9 +316,6 @@ struct receive_queue {
> > /* Is dynamic interrupt moderation enabled? */
> > bool dim_enabled;
> >
> >- /* Used to protect dim_enabled and inter_coal */
> >- struct mutex dim_lock;
> >-
> > /* Dynamic Interrupt Moderation */
> > struct dim dim;
> >
> >@@ -2368,10 +2365,6 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
> > /* Out of packets? */
> > if (received < budget) {
> > napi_complete = virtqueue_napi_complete(napi, rq->vq, received);
> >- /* Intentionally not taking dim_lock here. This may result in a
> >- * spurious net_dim call. But if that happens virtnet_rx_dim_work
> >- * will not act on the scheduled work.
> >- */
> > if (napi_complete && rq->dim_enabled)
> > virtnet_rx_dim_update(vi, rq);
> > }
> >@@ -3247,11 +3240,9 @@ static int virtnet_set_ringparam(struct net_device *dev,
> > return err;
> >
> > /* The reason is same as the transmit virtqueue reset */
> >- mutex_lock(&vi->rq[i].dim_lock);
> > err = virtnet_send_rx_ctrl_coal_vq_cmd(vi, i,
> > vi->intr_coal_rx.max_usecs,
> > vi->intr_coal_rx.max_packets);
> >- mutex_unlock(&vi->rq[i].dim_lock);
> > if (err)
> > return err;
> > }
> >@@ -4257,7 +4248,6 @@ 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))
> >@@ -4267,22 +4257,16 @@ 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++)
> > vi->rq[i].dim_enabled = true;
> >- goto unlock;
> >+ 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;
> >@@ -4300,10 +4284,8 @@ 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;
> >@@ -4311,11 +4293,8 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
> > 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,
> >@@ -4339,24 +4318,19 @@ static int virtnet_send_rx_notf_coal_vq_cmds(struct virtnet_info *vi,
> > u16 queue)
> > {
> > bool rx_ctrl_dim_on = !!ec->use_adaptive_rx_coalesce;
> >+ bool cur_rx_dim = vi->rq[queue].dim_enabled;
> > u32 max_usecs, max_packets;
> >- bool cur_rx_dim;
> > int err;
> >
> >- mutex_lock(&vi->rq[queue].dim_lock);
> >- cur_rx_dim = vi->rq[queue].dim_enabled;
> > max_usecs = vi->rq[queue].intr_coal.max_usecs;
> > max_packets = vi->rq[queue].intr_coal.max_packets;
> >
> > if (rx_ctrl_dim_on && (ec->rx_coalesce_usecs != max_usecs ||
> >- ec->rx_max_coalesced_frames != max_packets)) {
> >- mutex_unlock(&vi->rq[queue].dim_lock);
> >+ ec->rx_max_coalesced_frames != max_packets))
> > return -EINVAL;
> >- }
> >
> > if (rx_ctrl_dim_on && !cur_rx_dim) {
> > vi->rq[queue].dim_enabled = true;
> >- mutex_unlock(&vi->rq[queue].dim_lock);
> > return 0;
> > }
> >
> >@@ -4369,8 +4343,10 @@ static int virtnet_send_rx_notf_coal_vq_cmds(struct virtnet_info *vi,
> > err = virtnet_send_rx_ctrl_coal_vq_cmd(vi, queue,
> > ec->rx_coalesce_usecs,
> > ec->rx_max_coalesced_frames);
> >- mutex_unlock(&vi->rq[queue].dim_lock);
> >- return err;
> >+ if (err)
> >+ return err;
> >+
> >+ return 0;
> > }
> >
> > static int virtnet_send_notf_coal_vq_cmds(struct virtnet_info *vi,
> >@@ -4404,7 +4380,6 @@ static void virtnet_rx_dim_work(struct work_struct *work)
> >
> > qnum = rq - vi->rq;
> >
> >- mutex_lock(&rq->dim_lock);
> > if (!rq->dim_enabled)
> > goto out;
> >
> >@@ -4420,7 +4395,6 @@ static void virtnet_rx_dim_work(struct work_struct *work)
> > }
> > out:
> > dim->state = DIM_START_MEASURE;
> >- mutex_unlock(&rq->dim_lock);
> > }
> >
> > static int virtnet_coal_params_supported(struct ethtool_coalesce *ec)
> >@@ -4558,13 +4532,11 @@ static int virtnet_get_per_queue_coalesce(struct net_device *dev,
> > return -EINVAL;
> >
> > if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL)) {
> >- mutex_lock(&vi->rq[queue].dim_lock);
> > ec->rx_coalesce_usecs = vi->rq[queue].intr_coal.max_usecs;
> > ec->tx_coalesce_usecs = vi->sq[queue].intr_coal.max_usecs;
> > ec->tx_max_coalesced_frames = vi->sq[queue].intr_coal.max_packets;
> > ec->rx_max_coalesced_frames = vi->rq[queue].intr_coal.max_packets;
> > ec->use_adaptive_rx_coalesce = vi->rq[queue].dim_enabled;
> >- mutex_unlock(&vi->rq[queue].dim_lock);
> > } else {
> > ec->rx_max_coalesced_frames = 1;
> >
> >@@ -5396,7 +5368,6 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
> >
> > u64_stats_init(&vi->rq[i].stats.syncp);
> > u64_stats_init(&vi->sq[i].stats.syncp);
> >- mutex_init(&vi->rq[i].dim_lock);
> > }
> >
> > return 0;
> >--
> >2.32.0.3.g01195cf9f
> >
> >
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