The main threat to data consistency in ice_xdp() is a possible asynchronous
PF reset. It can be triggered by a user or by TX timeout handler.

XDP setup and PF reset code access the same resources in the following
sections:
* ice_vsi_close() in ice_prepare_for_reset() - already rtnl-locked
* ice_vsi_rebuild() for the PF VSI - not protected
* ice_vsi_open() - already rtnl-locked

With an unfortunate timing, such accesses can result in a crash such as the
one below:

[ +1.999878] ice 0000:b1:00.0: Registered XDP mem model MEM_TYPE_XSK_BUFF_POOL on Rx ring 14
[ +2.002992] ice 0000:b1:00.0: Registered XDP mem model MEM_TYPE_XSK_BUFF_POOL on Rx ring 18
[Mar15 18:17] ice 0000:b1:00.0 ens801f0np0: NETDEV WATCHDOG: CPU: 38: transmit queue 14 timed out 80692736 ms
[ +0.000093] ice 0000:b1:00.0 ens801f0np0: tx_timeout: VSI_num: 6, Q 14, NTC: 0x0, HW_HEAD: 0x0, NTU: 0x0, INT: 0x4000001
[ +0.000012] ice 0000:b1:00.0 ens801f0np0: tx_timeout recovery level 1, txqueue 14
[ +0.394718] ice 0000:b1:00.0: PTP reset successful
[ +0.006184] BUG: kernel NULL pointer dereference, address: 0000000000000098
[ +0.000045] #PF: supervisor read access in kernel mode
[ +0.000023] #PF: error_code(0x0000) - not-present page
[ +0.000023] PGD 0 P4D 0
[ +0.000018] Oops: 0000 [#1] PREEMPT SMP NOPTI
[ +0.000023] CPU: 38 PID: 7540 Comm: kworker/38:1 Not tainted 6.8.0-rc7 #1
[ +0.000031] Hardware name: Intel Corporation S2600WFT/S2600WFT, BIOS SE5C620.86B.02.01.0014.082620210524 08/26/2021
[ +0.000036] Workqueue: ice ice_service_task [ice]
[ +0.000183] RIP: 0010:ice_clean_tx_ring+0xa/0xd0 [ice]
[...]
[ +0.000013] Call Trace:
[ +0.000016] <TASK>
[ +0.000014] ? __die+0x1f/0x70
[ +0.000029] ? page_fault_oops+0x171/0x4f0
[ +0.000029] ? schedule+0x3b/0xd0
[ +0.000027] ? exc_page_fault+0x7b/0x180
[ +0.000022] ? asm_exc_page_fault+0x22/0x30
[ +0.000031] ? ice_clean_tx_ring+0xa/0xd0 [ice]
[ +0.000194] ice_free_tx_ring+0xe/0x60 [ice]
[ +0.000186] ice_destroy_xdp_rings+0x157/0x310 [ice]
[ +0.000151] ice_vsi_decfg+0x53/0xe0 [ice]
[ +0.000180] ice_vsi_rebuild+0x239/0x540 [ice]
[ +0.000186] ice_vsi_rebuild_by_type+0x76/0x180 [ice]
[ +0.000145] ice_rebuild+0x18c/0x840 [ice]
[ +0.000145] ? delay_tsc+0x4a/0xc0
[ +0.000022] ? delay_tsc+0x92/0xc0
[ +0.000020] ice_do_reset+0x140/0x180 [ice]
[ +0.000886] ice_service_task+0x404/0x1030 [ice]
[ +0.000824] process_one_work+0x171/0x340
[ +0.000685] worker_thread+0x277/0x3a0
[ +0.000675] ? preempt_count_add+0x6a/0xa0
[ +0.000677] ? _raw_spin_lock_irqsave+0x23/0x50
[ +0.000679] ? __pfx_worker_thread+0x10/0x10
[ +0.000653] kthread+0xf0/0x120
[ +0.000635] ? __pfx_kthread+0x10/0x10
[ +0.000616] ret_from_fork+0x2d/0x50
[ +0.000612] ? __pfx_kthread+0x10/0x10
[ +0.000604] ret_from_fork_asm+0x1b/0x30
[ +0.000604] </TASK>

The previous way of handling this through returning -EBUSY is not viable,
particularly when destroying AF_XDP socket, because the kernel proceeds
with removal anyway.

There is plenty of code between those calls and there is no need to create
a large critical section that covers all of them, same as there is no need
to protect ice_vsi_rebuild() with rtnl_lock().

Add xdp_state_lock mutex to protect ice_vsi_rebuild() and ice_xdp().

Leaving unprotected sections in between would result in two states that
have to be considered:
1. when the VSI is closed, but not yet rebuild
2. when VSI is already rebuild, but not yet open

The latter case is actually already handled through !netif_running() case,
we just need to adjust flag checking a little. The former one is not as
trivial, because between ice_vsi_close() and ice_vsi_rebuild(), a lot of
hardware interaction happens, this can make adding/deleting rings exit
with an error. Luckily, VSI rebuild is pending and can apply new
configuration for us in a managed fashion.

Therefore, add an additional VSI state flag ICE_VSI_REBUILD_PENDING to
indicate that ice_xdp() can just hot-swap the program.

Also, as ice_vsi_rebuild() flow is touched in this patch, make it more
consistent by deconfiguring VSI when coalesce allocation fails.

Fixes: 2d4238f5 ("ice: Add support for AF_XDP")
Fixes: efc2214b ("ice: Add support for XDP")
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Chandan Kumar Rout <chandanx.rout@intel.com>
Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>