net/mlx5e: Fix deadlock in tc route query code

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: Fix deadlock in tc route query code

Cited commit causes ABBA deadlock[0] when peer flows are created while
holding the devcom rw semaphore. Due to peer flows offload implementation
the lock is taken much higher up the call chain and there is no obvious way
to easily fix the deadlock. Instead, since tc route query code needs the
peer eswitch structure only to perform a lookup in xarray and doesn't
perform any sleeping operations with it, refactor the code for lockless
execution in following ways:

- RCUify the devcom 'data' pointer. When resetting the pointer
synchronously wait for RCU grace period before returning. This is fine
since devcom is currently only used for synchronization of
pairing/unpairing of eswitches which is rare and already expensive as-is.

- Wrap all usages of 'paired' boolean in {READ|WRITE}_ONCE(). The flag has
already been used in some unlocked contexts without proper
annotations (e.g. users of mlx5_devcom_is_paired() function), but it wasn't
an issue since all relevant code paths checked it again after obtaining the
devcom semaphore. Now it is also used by mlx5_devcom_get_peer_data_rcu() as
"best effort" check to return NULL when devcom is being unpaired. Note that
while RCU read lock doesn't prevent the unpaired flag from being changed
concurrently it still guarantees that reader can continue to use 'data'.

- Refactor mlx5e_tc_query_route_vport() function to use new
mlx5_devcom_get_peer_data_rcu() API which fixes the deadlock.

[0]:

[ 164.599612] ======================================================
[ 164.600142] WARNING: possible circular locking dependency detected
[ 164.600667] 6.3.0-rc3+ #1 Not tainted
[ 164.601021] ------------------------------------------------------
[ 164.601557] handler1/3456 is trying to acquire lock:
[ 164.601998] ffff88811f1714b0 (&esw->offloads.encap_tbl_lock){+.+.}-{3:3}, at: mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[ 164.603078]
but task is already holding lock:
[ 164.603617] ffff88810137fc98 (&comp->sem){++++}-{3:3}, at: mlx5_devcom_get_peer_data+0x37/0x80 [mlx5_core]
[ 164.604459]
which lock already depends on the new lock.

[ 164.605190]
the existing dependency chain (in reverse order) is:
[ 164.605848]
-> #1 (&comp->sem){++++}-{3:3}:
[ 164.606380] down_read+0x39/0x50
[ 164.606772] mlx5_devcom_get_peer_data+0x37/0x80 [mlx5_core]
[ 164.607336] mlx5e_tc_query_route_vport+0x86/0xc0 [mlx5_core]
[ 164.607914] mlx5e_tc_tun_route_lookup+0x1a4/0x1d0 [mlx5_core]
[ 164.608495] mlx5e_attach_decap_route+0xc6/0x1e0 [mlx5_core]
[ 164.609063] mlx5e_tc_add_fdb_flow+0x1ea/0x360 [mlx5_core]
[ 164.609627] __mlx5e_add_fdb_flow+0x2d2/0x430 [mlx5_core]
[ 164.610175] mlx5e_configure_flower+0x952/0x1a20 [mlx5_core]
[ 164.610741] tc_setup_cb_add+0xd4/0x200
[ 164.611146] fl_hw_replace_filter+0x14c/0x1f0 [cls_flower]
[ 164.611661] fl_change+0xc95/0x18a0 [cls_flower]
[ 164.612116] tc_new_tfilter+0x3fc/0xd20
[ 164.612516] rtnetlink_rcv_msg+0x418/0x5b0
[ 164.612936] netlink_rcv_skb+0x54/0x100
[ 164.613339] netlink_unicast+0x190/0x250
[ 164.613746] netlink_sendmsg+0x245/0x4a0
[ 164.614150] sock_sendmsg+0x38/0x60
[ 164.614522] ____sys_sendmsg+0x1d0/0x1e0
[ 164.614934] ___sys_sendmsg+0x80/0xc0
[ 164.615320] __sys_sendmsg+0x51/0x90
[ 164.615701] do_syscall_64+0x3d/0x90
[ 164.616083] entry_SYSCALL_64_after_hwframe+0x46/0xb0
[ 164.616568]
-> #0 (&esw->offloads.encap_tbl_lock){+.+.}-{3:3}:
[ 164.617210] __lock_acquire+0x159e/0x26e0
[ 164.617638] lock_acquire+0xc2/0x2a0
[ 164.618018] __mutex_lock+0x92/0xcd0
[ 164.618401] mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[ 164.618943] post_process_attr+0x153/0x2d0 [
---truncated---