vdpa/mlx5: Fix release of uninitialized resources on error path

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

vdpa/mlx5: Fix release of uninitialized resources on error path

The commit in the fixes tag made sure that mlx5_vdpa_free()

is the single entrypoint for removing the vdpa device resources

added in mlx5_vdpa_dev_add(), even in the cleanup path of

mlx5_vdpa_dev_add().

This means that all functions from mlx5_vdpa_free() should be able to

handle uninitialized resources. This was not the case though:

mlx5_vdpa_destroy_mr_resources() and mlx5_cmd_cleanup_async_ctx()

were not able to do so. This caused the splat below when adding

a vdpa device without a MAC address.

This patch fixes these remaining issues:

- Makes mlx5_vdpa_destroy_mr_resources() return early if called on

uninitialized resources.

- Moves mlx5_cmd_init_async_ctx() early on during device addition

because it can't fail. This means that mlx5_cmd_cleanup_async_ctx()

also can't fail. To mirror this, move the call site of

mlx5_cmd_cleanup_async_ctx() in mlx5_vdpa_free().

An additional comment was added in mlx5_vdpa_free() to document

the expectations of functions called from this context.

Splat:

mlx5_core 0000:b5:03.2: mlx5_vdpa_dev_add:3950:(pid 2306) warning: No mac address provisioned?

------------[ cut here ]------------

WARNING: CPU: 13 PID: 2306 at kernel/workqueue.c:4207 __flush_work+0x9a/0xb0

[...]

Call Trace:

<TASK>

? __try_to_del_timer_sync+0x61/0x90

? __timer_delete_sync+0x2b/0x40

mlx5_vdpa_destroy_mr_resources+0x1c/0x40 [mlx5_vdpa]

mlx5_vdpa_free+0x45/0x160 [mlx5_vdpa]

vdpa_release_dev+0x1e/0x50 [vdpa]

device_release+0x31/0x90

kobject_cleanup+0x37/0x130

mlx5_vdpa_dev_add+0x327/0x890 [mlx5_vdpa]

vdpa_nl_cmd_dev_add_set_doit+0x2c1/0x4d0 [vdpa]

genl_family_rcv_msg_doit+0xd8/0x130

genl_family_rcv_msg+0x14b/0x220

? __pfx_vdpa_nl_cmd_dev_add_set_doit+0x10/0x10 [vdpa]

genl_rcv_msg+0x47/0xa0

? __pfx_genl_rcv_msg+0x10/0x10

netlink_rcv_skb+0x53/0x100

genl_rcv+0x24/0x40

netlink_unicast+0x27b/0x3b0

netlink_sendmsg+0x1f7/0x430

__sys_sendto+0x1fa/0x210

? ___pte_offset_map+0x17/0x160

? next_uptodate_folio+0x85/0x2b0

? percpu_counter_add_batch+0x51/0x90

? filemap_map_pages+0x515/0x660

__x64_sys_sendto+0x20/0x30

do_syscall_64+0x7b/0x2c0

? do_read_fault+0x108/0x220

? do_pte_missing+0x14a/0x3e0

? __handle_mm_fault+0x321/0x730

? count_memcg_events+0x13f/0x180

? handle_mm_fault+0x1fb/0x2d0

? do_user_addr_fault+0x20c/0x700

? syscall_exit_work+0x104/0x140

entry_SYSCALL_64_after_hwframe+0x76/0x7e

RIP: 0033:0x7f0c25b0feca

[...]

---[ end trace 0000000000000000 ]---