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Message-ID: <1716371423.4910805-4-hengqi@linux.alibaba.com>
Date: Wed, 22 May 2024 17:50:23 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jiri Pirko <jiri@...nulli.us>,
netdev@...r.kernel.org,
virtualization@...ts.linux.dev,
Jason Wang <jasowang@...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 05:44:43 -0400, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Wed, May 22, 2024 at 04:52:19PM +0800, Heng Qi wrote:
> > 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:
>
> It's really hard to read this explanation.
>
> I think you mean is:
>
> 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, and we can not make each lock a separate class because
> there can be more than MAX_LOCKDEP_SUBCLASSES of vqs.
>
> However, dropping the lock is harmless.
Right.
>
>
>
> > > > 1. When dim is enabled, rx_dim_work may modify the coalescing parameters.
> > > > Users may read dirty coalescing parameters if querying.
>
>
> ... anyway?
>
> > > > 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.
>
> may be -> is?
Ok.
> How is this handled exactly?
Consider the following two scenarios a and b:
a.
1. dim is on
2. net_dim call schedules a worker
3. dim is turning off
4. The worker checks that dim is off and then exits after restoring dim's state.
5. The worker will not be scheduled until the next time dim is enabled.
b.
1. dim is on
2. net_dim call schedules a worker
3. The worker checks that dim is on and keeps going
4. dim is turning off
5. The worker successfully configure this parameter to the device.
6. The worker will not be scheduled until the next time dim is enabled.
>
> > > >
> > > >[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.
>
> Providing the subject of the reverted commit is helpful.
> Adding:
>
> Fixes: 4d4ac2ececd3 ("virtio_net: Add a lock for per queue RX coalesce")
>
> is a standard way to do that.
>
>
Will add.
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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