Function ice_plug_aux_dev() assigns pf->adev field too early prior
aux device initialization and on other side ice_unplug_aux_dev()
starts aux device deinit and at the end assigns NULL to pf->adev.
This is wrong because pf->adev should always be non-NULL only when
aux device is fully initialized and ready. This wrong order causes
a crash when ice_send_event_to_aux() call occurs because that function
depends on non-NULL value of pf->adev and does not assume that
aux device is half-initialized or half-destroyed.
After order correction the race window is tiny but it is still there,
as Leon mentioned and manipulation with pf->adev needs to be protected
by mutex.

Fix (un-)plugging functions so pf->adev field is set after aux device
init and prior aux device destroy and protect pf->adev assignment by
new mutex. This mutex is also held during ice_send_event_to_aux()
call to ensure that aux device is valid during that call.
Note that device lock used ice_send_event_to_aux() needs to be kept
to avoid race with aux drv unload.

Reproducer:
cycle=1
while :;do
        echo "#### Cycle: $cycle"

        ip link set ens7f0 mtu 9000
        ip link add bond0 type bond mode 1 miimon 100
        ip link set bond0 up
        ifenslave bond0 ens7f0
        ip link set bond0 mtu 9000
        ethtool -L ens7f0 combined 1
        ip link del bond0
        ip link set ens7f0 mtu 1500
        sleep 1

        let cycle++
done

In short when the device is added/removed to/from bond the aux device
is unplugged/plugged. When MTU of the device is changed an event is
sent to aux device asynchronously. This can race with (un)plugging
operation and because pf->adev is set too early (plug) or too late
(unplug) the function ice_send_event_to_aux() can touch uninitialized
or destroyed fields. In the case of crash below pf->adev->dev.mutex.

Crash:
[   53.372066] bond0: (slave ens7f0): making interface the new active one
[   53.378622] bond0: (slave ens7f0): Enslaving as an active interface with an u
p link
[   53.386294] IPv6: ADDRCONF(NETDEV_CHANGE): bond0: link becomes ready
[   53.549104] bond0: (slave ens7f1): Enslaving as a backup interface with an up
 link
[   54.118906] ice 0000:ca:00.0 ens7f0: Number of in use tx queues changed inval
idating tc mappings. Priority traffic classification disabled!
[   54.233374] ice 0000:ca:00.1 ens7f1: Number of in use tx queues changed inval
idating tc mappings. Priority traffic classification disabled!
[   54.248204] bond0: (slave ens7f0): Releasing backup interface
[   54.253955] bond0: (slave ens7f1): making interface the new active one
[   54.274875] bond0: (slave ens7f1): Releasing backup interface
[   54.289153] bond0 (unregistering): Released all slaves
[   55.383179] MII link monitoring set to 100 ms
[   55.398696] bond0: (slave ens7f0): making interface the new active one
[   55.405241] BUG: kernel NULL pointer dereference, address: 0000000000000080
[   55.405289] bond0: (slave ens7f0): Enslaving as an active interface with an u
p link
[   55.412198] #PF: supervisor write access in kernel mode
[   55.412200] #PF: error_code(0x0002) - not-present page
[   55.412201] PGD 25d2ad067 P4D 0
[   55.412204] Oops: 0002 [#1] PREEMPT SMP NOPTI
[   55.412207] CPU: 0 PID: 403 Comm: kworker/0:2 Kdump: loaded Tainted: G S
           5.17.0-13579-g57f2d6540f03 #1
[   55.429094] bond0: (slave ens7f1): Enslaving as a backup interface with an up
 link
[   55.430224] Hardware name: Dell Inc. PowerEdge R750/06V45N, BIOS 1.4.4 10/07/
2021
[   55.430226] Workqueue: ice ice_service_task [ice]
[   55.468169] RIP: 0010:mutex_unlock+0x10/0x20
[   55.472439] Code: 0f b1 13 74 96 eb e0 4c 89 ee eb d8 e8 79 54 ff ff 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 65 48 8b 04 25 40 ef 01 00 31 d2 <f0> 48 0f b1 17 75 01 c3 e9 e3 fe ff ff 0f 1f 00 0f 1f 44 00 00 48
[   55.491186] RSP: 0018:ff4454230d7d7e28 EFLAGS: 00010246
[   55.496413] RAX: ff1a79b208b08000 RBX: ff1a79b2182e8880 RCX: 0000000000000001
[   55.503545] RDX: 0000000000000000 RSI: ff4454230d7d7db0 RDI: 0000000000000080
[   55.510678] RBP: ff1a79d1c7e48b68 R08: ff4454230d7d7db0 R09: 0000000000000041
[   55.517812] R10: 00000000000000a5 R11: 00000000000006e6 R12: ff1a79d1c7e48bc0
[   55.524945] R13: 0000000000000000 R14: ff1a79d0ffc305c0 R15: 0000000000000000
[   55.532076] FS:  0000000000000000(0000) GS:ff1a79d0ffc00000(0000) knlGS:0000000000000000
[   55.540163] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   55.545908] CR2: 0000000000000080 CR3: 00000003487ae003 CR4: 0000000000771ef0
[   55.553041] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   55.560173] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   55.567305] PKRU: 55555554
[   55.570018] Call Trace:
[   55.572474]  <TASK>
[   55.574579]  ice_service_task+0xaab/0xef0 [ice]
[   55.579130]  process_one_work+0x1c5/0x390
[   55.583141]  ? process_one_work+0x390/0x390
[   55.587326]  worker_thread+0x30/0x360
[   55.590994]  ? process_one_work+0x390/0x390
[   55.595180]  kthread+0xe6/0x110
[   55.598325]  ? kthread_complete_and_exit+0x20/0x20
[   55.603116]  ret_from_fork+0x1f/0x30
[   55.606698]  </TASK>

Fixes: f9f5301e ("ice: Register auxiliary device to provide RDMA")
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Dave Ertman <david.m.ertman@intel.com>
Tested-by: Gurucharan <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>