tracefs: Use generic inode RCU for synchronizing freeing

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

tracefs: Use generic inode RCU for synchronizing freeing

With structure layout randomization enabled for 'struct inode' we need to
avoid overlapping any of the RCU-used / initialized-only-once members,
e.g. i_lru or i_sb_list to not corrupt related list traversals when making
use of the rcu_head.

For an unlucky structure layout of 'struct inode' we may end up with the
following splat when running the ftrace selftests:

[<...>] list_del corruption, ffff888103ee2cb0->next (tracefs_inode_cache+0x0/0x4e0 [slab object]) is NULL (prev is tracefs_inode_cache+0x78/0x4e0 [slab object])
[<...>] ------------[ cut here ]------------
[<...>] kernel BUG at lib/list_debug.c:54!
[<...>] invalid opcode: 0000 [#1] PREEMPT SMP KASAN
[<...>] CPU: 3 PID: 2550 Comm: mount Tainted: G N 6.8.12-grsec+ #122 ed2f536ca62f28b087b90e3cc906a8d25b3ddc65
[<...>] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
[<...>] RIP: 0010:[<ffffffff84656018>] __list_del_entry_valid_or_report+0x138/0x3e0
[<...>] Code: 48 b8 99 fb 65 f2 ff ff ff ff e9 03 5c d9 fc cc 48 b8 99 fb 65 f2 ff ff ff ff e9 33 5a d9 fc cc 48 b8 99 fb 65 f2 ff ff ff ff <0f> 0b 4c 89 e9 48 89 ea 48 89 ee 48 c7 c7 60 8f dd 89 31 c0 e8 2f
[<...>] RSP: 0018:fffffe80416afaf0 EFLAGS: 00010283
[<...>] RAX: 0000000000000098 RBX: ffff888103ee2cb0 RCX: 0000000000000000
[<...>] RDX: ffffffff84655fe8 RSI: ffffffff89dd8b60 RDI: 0000000000000001
[<...>] RBP: ffff888103ee2cb0 R08: 0000000000000001 R09: fffffbd0082d5f25
[<...>] R10: fffffe80416af92f R11: 0000000000000001 R12: fdf99c16731d9b6d
[<...>] R13: 0000000000000000 R14: ffff88819ad4b8b8 R15: 0000000000000000
[<...>] RBX: tracefs_inode_cache+0x0/0x4e0 [slab object]
[<...>] RDX: __list_del_entry_valid_or_report+0x108/0x3e0
[<...>] RSI: __func__.47+0x4340/0x4400
[<...>] RBP: tracefs_inode_cache+0x0/0x4e0 [slab object]
[<...>] RSP: process kstack fffffe80416afaf0+0x7af0/0x8000 [mount 2550 2550]
[<...>] R09: kasan shadow of process kstack fffffe80416af928+0x7928/0x8000 [mount 2550 2550]
[<...>] R10: process kstack fffffe80416af92f+0x792f/0x8000 [mount 2550 2550]
[<...>] R14: tracefs_inode_cache+0x78/0x4e0 [slab object]
[<...>] FS: 00006dcb380c1840(0000) GS:ffff8881e0600000(0000) knlGS:0000000000000000
[<...>] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[<...>] CR2: 000076ab72b30e84 CR3: 000000000b088004 CR4: 0000000000360ef0 shadow CR4: 0000000000360ef0
[<...>] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[<...>] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[<...>] ASID: 0003
[<...>] Stack:
[<...>] ffffffff818a2315 00000000f5c856ee ffffffff896f1840 ffff888103ee2cb0
[<...>] ffff88812b6b9750 0000000079d714b6 fffffbfff1e9280b ffffffff8f49405f
[<...>] 0000000000000001 0000000000000000 ffff888104457280 ffffffff8248b392
[<...>] Call Trace:
[<...>] <TASK>
[<...>] [<ffffffff818a2315>] ? lock_release+0x175/0x380 fffffe80416afaf0
[<...>] [<ffffffff8248b392>] list_lru_del+0x152/0x740 fffffe80416afb48
[<...>] [<ffffffff8248ba93>] list_lru_del_obj+0x113/0x280 fffffe80416afb88
[<...>] [<ffffffff8940fd19>] ? _atomic_dec_and_lock+0x119/0x200 fffffe80416afb90
[<...>] [<ffffffff8295b244>] iput_final+0x1c4/0x9a0 fffffe80416afbb8
[<...>] [<ffffffff8293a52b>] dentry_unlink_inode+0x44b/0xaa0 fffffe80416afbf8
[<...>] [<ffffffff8293fefc>] __dentry_kill+0x23c/0xf00 fffffe80416afc40
[<...>] [<ffffffff8953a85f>] ? __this_cpu_preempt_check+0x1f/0xa0 fffffe80416afc48
[<...>] [<ffffffff82949ce5>] ? shrink_dentry_list+0x1c5/0x760 fffffe80416afc70
[<...>] [<ffffffff82949b71>] ? shrink_dentry_list+0x51/0x760 fffffe80416afc78
[<...>] [<ffffffff82949da8>] shrink_dentry_list+0x288/0x760 fffffe80416afc80
[<...>] [<ffffffff8294ae75>] shrink_dcache_sb+0x155/0x420 fffffe80416afcc8
[<...>] [<ffffffff8953a7c3>] ? debug_smp_processor_id+0x23/0xa0 fffffe80416afce0
[<...>] [<ffffffff8294ad20>] ? do_one_tre
---truncated---