net/mlx5: Fix vhca_id access call trace use before alloc

net/mlx5: Fix vhca_id access call trace use before alloc

HCA CAP structure is allocated in mlx5_hca_caps_alloc().
mlx5_mdev_init()
  mlx5_hca_caps_alloc()

And HCA CAP is read from the device in mlx5_init_one().

The vhca_id's debugfs file is published even before above two
operations are done.
Due to this when user reads the vhca id before the initialization,
following call trace is observed.

Fix this by deferring debugfs publication until the HCA CAP is
allocated and read from the device.

BUG: kernel NULL pointer dereference, address: 0000000000000004
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP PTI
CPU: 23 UID: 0 PID: 6605 Comm: cat Kdump: loaded Not tainted 6.18.0-rc7-sf+ #110 PREEMPT(full)
Hardware name: Supermicro SYS-6028U-TR4+/X10DRU-i+, BIOS 2.0b 08/09/2016
RIP: 0010:vhca_id_show+0x17/0x30 [mlx5_core]
Code: cb 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 48 8b 47 70 48 c7 c6 45 f0 12 c1 48 8b 80 70 03 00 00 <8b> 50 04 0f ca 0f b7 d2 e8 8c 82 47 cb 31 c0 c3 cc cc cc cc 0f 1f
RSP: 0018:ffffd37f4f337d40 EFLAGS: 00010203
RAX: 0000000000000000 RBX: ffff8f18445c9b40 RCX: 0000000000000001
RDX: ffff8f1109825180 RSI: ffffffffc112f045 RDI: ffff8f18445c9b40
RBP: 0000000000000000 R08: 0000645eac0d2928 R09: 0000000000000006
R10: ffffd37f4f337d48 R11: 0000000000000000 R12: ffffd37f4f337dd8
R13: ffffd37f4f337db0 R14: ffff8f18445c9b68 R15: 0000000000000001
FS:  00007f3eea099580(0000) GS:ffff8f2090f1f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000004 CR3: 00000008b64e4006 CR4: 00000000003726f0
Call Trace:
 <TASK>
 seq_read_iter+0x11f/0x4f0
 ? _raw_spin_unlock+0x15/0x30
 ? do_anonymous_page+0x104/0x810
 seq_read+0xf6/0x120
 ? srso_alias_untrain_ret+0x1/0x10
 full_proxy_read+0x5c/0x90
 vfs_read+0xad/0x320
 ? handle_mm_fault+0x1ab/0x290
 ksys_read+0x52/0xd0
 do_syscall_64+0x61/0x11e0
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fixes: dd3dd7263cde ("net/mlx5: Expose vhca_id to debugfs")
Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Shay Drori <shayd@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1769503961-124173-4-git-send-email-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>