Use mutex_lock_nested to provide lockdep the parent child lock ordering of
the tree.

This fixes the lockdep Warning
[  305.275177] ============================================
[  305.275178] WARNING: possible recursive locking detected
[  305.275179] 4.14.0-rc7+ #320 Not tainted
[  305.275180] --------------------------------------------
[  305.275181] apparmor_parser/1339 is trying to acquire lock:
[  305.275182]  (&ns->lock){+.+.}, at: [<ffffffff970544dd>] __aa_create_ns+0x6d/0x1e0
[  305.275187]
               but task is already holding lock:
[  305.275187]  (&ns->lock){+.+.}, at: [<ffffffff97054b5d>] aa_prepare_ns+0x3d/0xd0
[  305.275190]
               other info that might help us debug this:
[  305.275191]  Possible unsafe locking scenario:

[  305.275192]        CPU0
[  305.275193]        ----
[  305.275193]   lock(&ns->lock);
[  305.275194]   lock(&ns->lock);
[  305.275195]
                *** DEADLOCK ***

[  305.275196]  May be due to missing lock nesting notation

[  305.275198] 2 locks held by apparmor_parser/1339:
[  305.275198]  #0:  (sb_writers#10){.+.+}, at: [<ffffffff96e9c6b7>] vfs_write+0x1a7/0x1d0
[  305.275202]  #1:  (&ns->lock){+.+.}, at: [<ffffffff97054b5d>] aa_prepare_ns+0x3d/0xd0
[  305.275205]
               stack backtrace:
[  305.275207] CPU: 1 PID: 1339 Comm: apparmor_parser Not tainted 4.14.0-rc7+ #320
[  305.275208] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014
[  305.275209] Call Trace:
[  305.275212]  dump_stack+0x85/0xcb
[  305.275214]  __lock_acquire+0x141c/0x1460
[  305.275216]  ? __aa_create_ns+0x6d/0x1e0
[  305.275218]  ? ___slab_alloc+0x183/0x540
[  305.275219]  ? ___slab_alloc+0x183/0x540
[  305.275221]  lock_acquire+0xed/0x1e0
[  305.275223]  ? lock_acquire+0xed/0x1e0
[  305.275224]  ? __aa_create_ns+0x6d/0x1e0
[  305.275227]  __mutex_lock+0x89/0x920
[  305.275228]  ? __aa_create_ns+0x6d/0x1e0
[  305.275230]  ? trace_hardirqs_on_caller+0x11f/0x190
[  305.275231]  ? __aa_create_ns+0x6d/0x1e0
[  305.275233]  ? __lockdep_init_map+0x57/0x1d0
[  305.275234]  ? lockdep_init_map+0x9/0x10
[  305.275236]  ? __rwlock_init+0x32/0x60
[  305.275238]  mutex_lock_nested+0x1b/0x20
[  305.275240]  ? mutex_lock_nested+0x1b/0x20
[  305.275241]  __aa_create_ns+0x6d/0x1e0
[  305.275243]  aa_prepare_ns+0xc2/0xd0
[  305.275245]  aa_replace_profiles+0x168/0xf30
[  305.275247]  ? __might_fault+0x85/0x90
[  305.275250]  policy_update+0xb9/0x380
[  305.275252]  profile_load+0x7e/0x90
[  305.275254]  __vfs_write+0x28/0x150
[  305.275256]  ? rcu_read_lock_sched_held+0x72/0x80
[  305.275257]  ? rcu_sync_lockdep_assert+0x2f/0x60
[  305.275259]  ? __sb_start_write+0xdc/0x1c0
[  305.275261]  ? vfs_write+0x1a7/0x1d0
[  305.275262]  vfs_write+0xca/0x1d0
[  305.275264]  ? trace_hardirqs_on_caller+0x11f/0x190
[  305.275266]  SyS_write+0x49/0xa0
[  305.275268]  entry_SYSCALL_64_fastpath+0x23/0xc2
[  305.275271] RIP: 0033:0x7fa6b22e8c74
[  305.275272] RSP: 002b:00007ffeaaee6288 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[  305.275273] RAX: ffffffffffffffda RBX: 00007ffeaaee62a4 RCX: 00007fa6b22e8c74
[  305.275274] RDX: 0000000000000a51 RSI: 00005566a8198c10 RDI: 0000000000000004
[  305.275275] RBP: 0000000000000a39 R08: 0000000000000a51 R09: 0000000000000000
[  305.275276] R10: 0000000000000000 R11: 0000000000000246 R12: 00005566a8198c10
[  305.275277] R13: 0000000000000004 R14: 00005566a72ecb88 R15: 00005566a72ec3a8

Fixes: 73688d1e

 ("apparmor: refactor prepare_ns() and make usable from different views")
Signed-off-by: John Johansen <john.johansen@canonical.com>