Date: Wed, 22 May 2024 12:51:51 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Heng Qi <hengqi@...ux.alibaba.com>
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"

Wed, May 22, 2024 at 10:52:19AM CEST, hengqi@...ux.alibaba.com 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

Correct.


>
>> 
>> >
>> >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.

For submissions to -net, you always need the Fixes tag. As this fixes
bug introduced by 4d4ac2ececd3c42a08dd32a6e3a4aaf25f7efe44, you should
put that in "Fixes".


>
>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
>> >
>> >

Powered by blists - more mailing lists