net: only give queue leasing devices a separate instance lock class

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Commit b6f74dff6d ("net: use two lockdep classes for the netdev
instance lock") put every device without a parent in the virtual class.
It also restricted the locking order for the virtual class, because
queue leasing has hard requirements on the exact order.

This bites us back on bond, which is "virtual" and needs to be taken
before taking the locks of the lowers. NIPA hit the following on the
new test I recently posted for XDP+bond:

  WARNING: possible circular locking dependency detected
  ------------------------------------------------------
  python3/18635 is trying to acquire lock:
  ff11000120b8ce30 (&dev->lock){+.+.}-{4:4}, at:
  netdev_put_lock+0x2d/0x1a0

  but task is already holding lock:
  ff110001ef77ae30 (&netdev_virt_instance_lock_key){+.+.}-{4:4}, at:
  netdev_put_lock+0x2d/0x1a0

  which lock already depends on the new lock.

  the existing dependency chain (in reverse order) is:

  -> #1 (&netdev_virt_instance_lock_key){+.+.}-{4:4}:
         __mutex_lock+0x1ae/0x1f10
         xdp_set_features_flag+0x2b/0x50
         bond_xdp_set_features+0x1eb/0x360
         bond_netdev_event+0x13f/0x300
         notifier_call_chain+0xae/0x300
         call_netdevice_notifiers+0x70/0xa0
         bnxt_xdp_set+0x2f6/0x620
         netif_xdp_propagate+0x503/0xc60
         dev_xdp_propagate+0xa1/0x230
         bond_xdp_set+0x234/0x700
         dev_xdp_install+0x592/0xd70
         dev_xdp_attach+0x355/0xf50
         dev_change_xdp_fd+0x176/0x210
         do_setlink.isra.0+0x220d/0x2b20
         rtnl_newlink+0x9f1/0x11b0

  -> #0 (&dev->lock){+.+.}-{4:4}:
         __mutex_lock+0x1ae/0x1f10
         netdev_put_lock+0x2d/0x1a0
         netdev_nl_queue_create_doit+0x801/0x1a70
         genl_family_rcv_msg_doit+0x206/0x300

   Possible unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(&netdev_virt_instance_lock_key);
                                 lock(&dev->lock);
                                 lock(&netdev_virt_instance_lock_key);
    lock(&dev->lock);

Let's narrow down the "virtual" class to only the devices which
can actually create a queue. More LoC and complexity, but that
is what we actually care about here. The rest needs to nest
under rtnl_lock, which bond does (famous last words?)

Take the instance locks in two passes, first the netkits then
the rest (matching the queue leasing order).
An alternative would be to make sure the close list is sorted
correctly from the start (queue head/tail appropriately in
unregister_netdevice_queue()). I think it works but feels
a little more fragile. Happy to change, tho.

netdev_can_create_queue() will now be used on paths where we
genuinely handle non-netkit, so we can't always set the extack.
Unfortunately, the (recently) added tracepoint in extack fires
even when extack is NULL.

Fixes: b6f74dff6d ("net: use two lockdep classes for the netdev instance lock")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://patch.msgid.link/20260929191543.3295633-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

...

This commit is contained in:

Jakub Kicinski 2026-09-29 12:15:43 -07:00 • committed by Paolo Abeni

parent 69d9c07dc8

commit ddef4c2d6d

2 changed files with 44 additions and 35 deletions

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48

net/core/dev.c

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31

net/core/netdev_queues.c

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