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@xxxxxxxxxxx> wrote: > > Wed, May 22, 2024 at 05:45:48AM CEST, hengqi@xxxxxxxxxxxxxxxxx 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. > > > 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? How is this handled exactly? > > > > > >[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@xxxxxxxxxxxxxxxxx> > > > > 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. > > > > > > >--- > > > 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 > > > > > >
