Re: [PATCH net-next v3 04/13] net: move promiscuity handling into dev_rx_mode_work

[Stanislav Fomichev <stfomichev@gmail.com>]

On 03/20, Loktionov, Aleksandr wrote:
> 
> 
> > -----Original Message-----
> > From: Stanislav Fomichev <sdf@fomichev.me>
> > Sent: Friday, March 20, 2026 2:25 AM
> > To: netdev@vger.kernel.org
> > Cc: davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
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> > michael.chan@broadcom.com; pavan.chebbi@broadcom.com; Nguyen, Anthony
> > L <anthony.l.nguyen@intel.com>; Kitszel, Przemyslaw
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> > Jacob E <jacob.e.keller@intel.com>; willemb@google.com;
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> > <aleksandr.loktionov@intel.com>; kees@kernel.org; linux-
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> > leon@kernel.org
> > Subject: [PATCH net-next v3 04/13] net: move promiscuity handling into
> > dev_rx_mode_work
> > 
> > Move unicast promiscuity tracking into dev_rx_mode_work so it runs
> > under netdev_ops_lock instead of under the addr_lock spinlock. This is
> > required because __dev_set_promiscuity calls dev_change_rx_flags and
> > __dev_notify_flags, both of which may need to sleep.
> > 
> > Change ASSERT_RTNL() to netdev_ops_assert_locked() in
> > __dev_set_promiscuity, netif_set_allmulti and __dev_change_flags since
> > these are now called from the work queue under the ops lock.
> > 
> > Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
> > Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
> > ---
> >  Documentation/networking/netdevices.rst |  4 ++
> >  net/core/dev.c                          | 79 +++++++++++++++++-------
> > -
> >  2 files changed, 57 insertions(+), 26 deletions(-)
> > 
> > diff --git a/Documentation/networking/netdevices.rst
> > b/Documentation/networking/netdevices.rst
> > index dc83d78d3b27..5cdaa1a3dcc8 100644
> > --- a/Documentation/networking/netdevices.rst
> > +++ b/Documentation/networking/netdevices.rst
> > @@ -298,6 +298,10 @@ struct net_device synchronization rules
> >  	Notes: Sleepable version of ndo_set_rx_mode. Receives snapshots
> >  	of the unicast and multicast address lists.
> > 
> > +ndo_change_rx_flags:
> > +	Synchronization: rtnl_lock() semaphore. In addition, netdev
> > instance
> > +	lock if the driver implements queue management or shaper API.
> > +
> >  ndo_setup_tc:
> >  	``TC_SETUP_BLOCK`` and ``TC_SETUP_FT`` are running under NFT
> > locks
> >  	(i.e. no ``rtnl_lock`` and no device instance lock). The rest
> > of diff --git a/net/core/dev.c b/net/core/dev.c index
> > fedc423306fc..fc5c9b14faa0 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -9574,7 +9574,7 @@ static int __dev_set_promiscuity(struct
> > net_device *dev, int inc, bool notify)
> >  	kuid_t uid;
> >  	kgid_t gid;
> > 
> > -	ASSERT_RTNL();
> > +	netdev_ops_assert_locked(dev);
> Can you explain why do you add new hard precondition of ops lock must be held?

The context is that in f792709e0baa ("selftests: net: validate team flags
propagation") I had to add locking around NETDEV_CHANGE notifiers and
add that ugly `if (notify) netdev_ops_assert_locked` check. After this
patch I believe we are consistently calling __dev_set_promiscuity
with the ops lock (for ops locked netdev), so we can cleanup this enforcement
part. 

> >  	promiscuity = dev->promiscuity + inc;
> >  	if (promiscuity == 0) {
> > @@ -9610,16 +9610,8 @@ static int __dev_set_promiscuity(struct
> > net_device *dev, int inc, bool notify)
> > 
> >  		dev_change_rx_flags(dev, IFF_PROMISC);
> >  	}
> 
> ...
> 
> >  	__hw_addr_init(&uc_snap);
> > @@ -9704,16 +9720,29 @@ static void dev_rx_mode_work(struct
> > work_struct *work)
> >  		if (!err)
> >  			err = __hw_addr_list_snapshot(&mc_ref, &dev->mc,
> >  						      dev->addr_len);
> > -		netif_addr_unlock_bh(dev);
> > 
> >  		if (err) {
> >  			netdev_WARN(dev, "failed to sync uc/mc
> > addresses\n");
> >  			__hw_addr_flush(&uc_snap);
> >  			__hw_addr_flush(&uc_ref);
> >  			__hw_addr_flush(&mc_snap);
> > +			netif_addr_unlock_bh(dev);
> >  			goto out;
> >  		}
> > 
> > +		promisc_inc = dev_uc_promisc_update(dev);
> > +
> > +		netif_addr_unlock_bh(dev);
> > +	} else {
> > +		netif_addr_lock_bh(dev);
> > +		promisc_inc = dev_uc_promisc_update(dev);
> > +		netif_addr_unlock_bh(dev);
> > +	}
> > +
> > +	if (promisc_inc)
> > +		__dev_set_promiscuity(dev, promisc_inc, false);
> But it's being called here without any netdev_lock_ops(dev) ?

We have the following at the start of dev_rx_mode_work:
  rtnl_lock();
  netdev_lock_ops(dev);

Or am I looking at something else?