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Message-ID: <Z8JMjmqvct6rbidn@mini-arch>
Date: Fri, 28 Feb 2025 15:53:50 -0800
From: Stanislav Fomichev <stfomichev@...il.com>
To: Saeed Mahameed <saeed@...nel.org>
Cc: Stanislav Fomichev <sdf@...ichev.me>, netdev@...r.kernel.org,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com
Subject: Re: [PATCH net-next v9 01/12] net: hold netdev instance lock during
ndo_open/ndo_stop
On 02/28, Saeed Mahameed wrote:
> On 27 Feb 20:53, Stanislav Fomichev wrote:
> > For the drivers that use shaper API, switch to the mode where
> > core stack holds the netdev lock. This affects two drivers:
> >
> > * iavf - already grabs netdev lock in ndo_open/ndo_stop, so mostly
> > remove these
> > * netdevsim - switch to _locked APIs to avoid deadlock
> >
> > iavf_close diff is a bit confusing, the existing call looks like this:
> > iavf_close() {
> > netdev_lock()
> > ..
> > netdev_unlock()
> > wait_event_timeout(down_waitqueue)
> > }
> >
> > I change it to the following:
> > netdev_lock()
> > iavf_close() {
> > ..
> > netdev_unlock()
> > wait_event_timeout(down_waitqueue)
> > netdev_lock() // reusing this lock call
> > }
> > netdev_unlock()
> >
> > Since I'm reusing existing netdev_lock call, so it looks like I only
> > add netdev_unlock.
> >
> > Cc: Saeed Mahameed <saeed@...nel.org>
> > Signed-off-by: Stanislav Fomichev <sdf@...ichev.me>
> > ---
> > drivers/net/ethernet/intel/iavf/iavf_main.c | 14 ++++++-------
> > drivers/net/netdevsim/netdev.c | 14 ++++++++-----
> > include/linux/netdevice.h | 23 +++++++++++++++++++++
> > net/core/dev.c | 12 +++++++++++
> > net/core/dev.h | 6 ++++--
> > 5 files changed, 54 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/iavf/iavf_main.c b/drivers/net/ethernet/intel/iavf/iavf_main.c
> > index 71f11f64b13d..9f4d223dffcf 100644
> > --- a/drivers/net/ethernet/intel/iavf/iavf_main.c
> > +++ b/drivers/net/ethernet/intel/iavf/iavf_main.c
> > @@ -4562,22 +4562,21 @@ static int iavf_open(struct net_device *netdev)
> > struct iavf_adapter *adapter = netdev_priv(netdev);
> > int err;
> >
> > + netdev_assert_locked(netdev);
> > +
> > if (adapter->flags & IAVF_FLAG_PF_COMMS_FAILED) {
> > dev_err(&adapter->pdev->dev, "Unable to open device due to PF driver failure.\n");
> > return -EIO;
> > }
> >
> > - netdev_lock(netdev);
> > while (!mutex_trylock(&adapter->crit_lock)) {
> > /* If we are in __IAVF_INIT_CONFIG_ADAPTER state the crit_lock
> > * is already taken and iavf_open is called from an upper
> > * device's notifier reacting on NETDEV_REGISTER event.
> > * We have to leave here to avoid dead lock.
> > */
> > - if (adapter->state == __IAVF_INIT_CONFIG_ADAPTER) {
> > - netdev_unlock(netdev);
> > + if (adapter->state == __IAVF_INIT_CONFIG_ADAPTER)
> > return -EBUSY;
> > - }
> >
> > usleep_range(500, 1000);
> > }
> > @@ -4626,7 +4625,6 @@ static int iavf_open(struct net_device *netdev)
> > iavf_irq_enable(adapter, true);
> >
> > mutex_unlock(&adapter->crit_lock);
> > - netdev_unlock(netdev);
> >
> > return 0;
> >
> > @@ -4639,7 +4637,6 @@ static int iavf_open(struct net_device *netdev)
> > iavf_free_all_tx_resources(adapter);
> > err_unlock:
> > mutex_unlock(&adapter->crit_lock);
> > - netdev_unlock(netdev);
> >
> > return err;
> > }
> > @@ -4661,12 +4658,12 @@ static int iavf_close(struct net_device *netdev)
> > u64 aq_to_restore;
> > int status;
> >
> > - netdev_lock(netdev);
> > + netdev_assert_locked(netdev);
> > +
> > mutex_lock(&adapter->crit_lock);
> >
> > if (adapter->state <= __IAVF_DOWN_PENDING) {
> > mutex_unlock(&adapter->crit_lock);
> > - netdev_unlock(netdev);
> > return 0;
> > }
> >
> > @@ -4719,6 +4716,7 @@ static int iavf_close(struct net_device *netdev)
> > if (!status)
> > netdev_warn(netdev, "Device resources not yet released\n");
> >
> > + netdev_lock(netdev);
> > mutex_lock(&adapter->crit_lock);
> > adapter->aq_required |= aq_to_restore;
> > mutex_unlock(&adapter->crit_lock);
> > diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
> > index a41dc79e9c2e..aaa3b58e2e3e 100644
> > --- a/drivers/net/netdevsim/netdev.c
> > +++ b/drivers/net/netdevsim/netdev.c
> > @@ -402,7 +402,7 @@ static int nsim_init_napi(struct netdevsim *ns)
> > for (i = 0; i < dev->num_rx_queues; i++) {
> > rq = ns->rq[i];
> >
> > - netif_napi_add_config(dev, &rq->napi, nsim_poll, i);
> > + netif_napi_add_config_locked(dev, &rq->napi, nsim_poll, i);
> > }
> >
> > for (i = 0; i < dev->num_rx_queues; i++) {
> > @@ -422,7 +422,7 @@ static int nsim_init_napi(struct netdevsim *ns)
> > }
> >
> > for (i = 0; i < dev->num_rx_queues; i++)
> > - __netif_napi_del(&ns->rq[i]->napi);
> > + __netif_napi_del_locked(&ns->rq[i]->napi);
> >
> > return err;
> > }
> > @@ -452,7 +452,7 @@ static void nsim_enable_napi(struct netdevsim *ns)
> > struct nsim_rq *rq = ns->rq[i];
> >
> > netif_queue_set_napi(dev, i, NETDEV_QUEUE_TYPE_RX, &rq->napi);
> > - napi_enable(&rq->napi);
> > + napi_enable_locked(&rq->napi);
> > }
> > }
> >
> > @@ -461,6 +461,8 @@ static int nsim_open(struct net_device *dev)
> > struct netdevsim *ns = netdev_priv(dev);
> > int err;
> >
> > + netdev_assert_locked(dev);
> > +
> > err = nsim_init_napi(ns);
> > if (err)
> > return err;
> > @@ -478,8 +480,8 @@ static void nsim_del_napi(struct netdevsim *ns)
> > for (i = 0; i < dev->num_rx_queues; i++) {
> > struct nsim_rq *rq = ns->rq[i];
> >
> > - napi_disable(&rq->napi);
> > - __netif_napi_del(&rq->napi);
> > + napi_disable_locked(&rq->napi);
> > + __netif_napi_del_locked(&rq->napi);
> > }
> > synchronize_net();
> >
> > @@ -494,6 +496,8 @@ static int nsim_stop(struct net_device *dev)
> > struct netdevsim *ns = netdev_priv(dev);
> > struct netdevsim *peer;
> >
> > + netdev_assert_locked(dev);
> > +
> > netif_carrier_off(dev);
> > peer = rtnl_dereference(ns->peer);
> > if (peer)
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 26a0c4e4d963..24d54c7e60c2 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -2753,6 +2753,29 @@ static inline void netdev_assert_locked_or_invisible(struct net_device *dev)
> > netdev_assert_locked(dev);
> > }
> >
> > +static inline bool netdev_need_ops_lock(struct net_device *dev)
> > +{
> > + bool ret = false;
> > +
> > +#if IS_ENABLED(CONFIG_NET_SHAPER)
> > + ret |= !!dev->netdev_ops->net_shaper_ops;
> > +#endif
> > +
> > + return ret;
> > +}
> > +
> > +static inline void netdev_lock_ops(struct net_device *dev)
> > +{
> > + if (netdev_need_ops_lock(dev))
> > + netdev_lock(dev);
> > +}
> > +
> > +static inline void netdev_unlock_ops(struct net_device *dev)
> > +{
> > + if (netdev_need_ops_lock(dev))
> > + netdev_unlock(dev);
> > +}
> > +
> > void netif_napi_set_irq_locked(struct napi_struct *napi, int irq);
> >
> > static inline void netif_napi_set_irq(struct napi_struct *napi, int irq)
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index d6d68a2d2355..5b1b68cb4a25 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -1627,6 +1627,8 @@ static int __dev_open(struct net_device *dev, struct netlink_ext_ack *extack)
> > if (ret)
> > return ret;
> >
> > + netdev_lock_ops(dev);
> > +
>
> Hi Stan,
>
> Just started testing this before review and I hit a deadlock when applying
> the patch that implements qmgmt in mlx5.
>
> deadlock:
> _dev_open() [netdev_lock_ops(dev)] ==> 1st time lock
> dev_activate() -> attach_default_qdiscs()->
> qdisc_create_dflt()->
> mq_init()-> mq_offload() ->
> dev_setup_tc(dev) [netdev_lock_ops(dev)] ==> 2nd :- double lock
>
> I am not sure how to solve this right now, since the qdisc API is reached
> by callbacks and it's not trivial to select which version of dev_setup_tc()
> to call, locked or non locked, the only direction i have right now is that
> attached_default_qdiscs is only called by dev_activate() if we can assume
> dev_activate() is always netdev_locked, then we can somehow signal that to
> mq_offload().
Oh, oh, thanks for the report! I'm a bit surprised I haven't seen it
on my side with bnxt.
I'm thinking about moving the locking part up into tc_modify_qdisc layer (and
keep DSA/NFT as is). Let me try to see if it's gonna work..
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