Revert "Fix: update block instrumentation for kernel 4.14"

Revert "Fix: update block instrumentation for kernel 4.14"

This reverts commit 49447902967115fe5a07ee7a1df3d17fbf4b1ab8.

It introduces a NULL pointer dereference:

[ 37.862398] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
181.3  [ 37.864108] IP: [<ffffffffa01c41b7>] __event_probe__block_get_rq+0x127/0x4b0 [lttng_probe_block]
181.4  [ 37.864108] PGD 7a402067 PUD 7a4c7067 PMD 0
181.5  [ 37.864108] Oops: 0000 [#1] SMP
181.6  [ 37.864108] Modules linked in: lttng_probe_x86_exceptions(OE) lttng_probe_x86_irq_vectors(OE) lttng_probe_writeback(OE) lttng_probe_workqueue(OE) lttng_probe_vmscan(OE) lttng_probe_udp(OE) lttng_probe_timer(OE) lttng_probe_sunrpc(OE) lttng_probe_statedump(OE) lttng_probe_sock(OE) lttng_probe_skb(OE) lttng_probe_signal(OE) lttng_probe_scsi(OE) lttng_probe_sched(OE) lttng_probe_regulator(OE) lttng_probe_regmap(OE) lttng_probe_rcu(OE) lttng_probe_random(OE) lttng_probe_printk(OE) lttng_probe_power(OE) lttng_probe_net(OE) lttng_probe_napi(OE) lttng_probe_module(OE) lttng_probe_kvm_x86_mmu(OE) lttng_probe_kvm_x86(OE) lttng_probe_kvm(OE) lttng_probe_kmem(OE) lttng_probe_jbd2(OE) lttng_probe_irq(OE) lttng_probe_i2c(OE) lttng_probe_gpio(OE) lttng_probe_ext4(OE) lttng_probe_compaction(OE) lttng_probe_btrfs(OE) lttng_probe_block(OE) lttng_ring_buffer_metadata_mmap_client(OE) lttng_ring_buffer_client_mmap_overwrite(OE) lttng_ring_buffer_client_mmap_discard(OE) lttng_ring_buffer_metadata_client(OE) lttng_ring_buffer_client_overwrite(OE) lttng_ring_buffer_client_discard(OE) lttng_tracer(OE) lttng_statedump(OE) lttng_ftrace(OE) lttng_kprobes(OE) lttng_clock(OE) lttng_lib_ring_buffer(OE) lttng_kretprobes(OE)
181.7  [ 37.864108] CPU: 1 PID: 6 Comm: kworker/u4:0 Tainted: G OE 4.4.90 #1
181.8  [ 37.864108] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
181.9  [ 37.864108] Workqueue: events_freezable_power_ disk_events_workfn
181.10  [ 37.864108] task: ffff88007c861bc0 ti: ffff88007c868000 task.ti: ffff88007c868000
181.11  [ 37.864108] RIP: 0010:[<ffffffffa01c41b7>] [<ffffffffa01c41b7>] __event_probe__block_get_rq+0x127/0x4b0 [lttng_probe_block]
181.12  [ 37.864108] RSP: 0018:ffff88007c86ba98 EFLAGS: 00010246
181.13  [ 37.864108] RAX: 0000000000000000 RBX: ffff880073683348 RCX: ffff8800747d0000
181.14  [ 37.864108] RDX: 00000008d0c5bde9 RSI: 00000000000009f2 RDI: 0000000000400000
181.15  [ 37.864108] RBP: ffff88007c86bba8 R08: 00000000001789ed R09: 0000000000100000
181.16  [ 37.864108] R10: ffffe8ffffd02460 R11: 0000000000000000 R12: 0000000000000000
181.17  [ 37.864108] R13: 0000000000017fe0 R14: ffff88007363c6e8 R15: ffff88007bef83c0
181.18  [ 37.864108] FS: 0000000000000000(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000
181.19  [ 37.864108] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
181.20  [ 37.864108] CR2: 0000000000000008 CR3: 000000007a4d0000 CR4: 00000000000006e0
181.21  [ 37.864108] Stack:
181.22  [ 37.864108] 0000000000000000 ffffffff8115a46b ffff88007c86bbe8 ffff88007bc67e30
181.23  [ 37.864108] ffff880073683348 00000000ffffff01 ffff88007a7a1000 ffff88007c86bab8
181.24  [ 37.864108] 0000000000000028 0000000100000001 ffffe8ffffd02460 0000000000000035
181.25  [ 37.864108] Call Trace:
181.26  [ 37.864108] [<ffffffff8115a46b>] ? ktime_get_mono_fast_ns+0x4b/0x90
181.27  [ 37.864108] [<ffffffff81532849>] ? alloc_request_struct+0x19/0x20
181.28  [ 37.864108] [<ffffffff811e8d8f>] ? mempool_alloc+0x5f/0x150
181.29  [ 37.864108] [<ffffffffa021815c>] ? __event_probe__kmem_alloc+0x1dc/0x2c0 [lttng_probe_kmem]
181.30  [ 37.864108] [<ffffffff810ad85e>] ? kvm_clock_read+0x1e/0x20
181.31  [ 37.864108] [<ffffffff81535f4f>] get_request+0x4af/0x760
181.32  [ 37.864108] [<ffffffff8112c270>] ? wake_atomic_t_function+0x60/0x60
181.33  [ 37.864108] [<ffffffff81536283>] blk_get_request+0x83/0xe0
181.34  [ 37.864108] [<ffffffff81773b5d>] scsi_execute+0x3d/0x1d0
181.35  [ 37.864108] [<ffffffff817758fe>] scsi_execute_req_flags+0x8e/0xf0
181.36  [ 37.864108] [<ffffffff81788f4d>] sr_check_events+0x8d/0x2a0
181.37  [ 37.864108] [<ffffffff81547590>] ? disk_check_events+0x130/0x130
181.38  [ 37.864108] [<ffffffff8181b618>] cdrom_check_events+0x18/0x30
181.39  [ 37.864108] [<ffffffff8178935a>] sr_block_check_events+0x2a/0x30
181.40  [ 37.864108] [<ffffffff815474b1>] disk_check_events+0x51/0x130
181.41  [ 37.864108] [<ffffffff815475a6>] disk_events_workfn+0x16/0x20
181.42  [ 37.864108] [<ffffffff81102b85>] process_one_work+0x165/0x480
181.43  [ 37.864108] [<ffffffff81102eeb>] worker_thread+0x4b/0x4c0
181.44  [ 37.864108] [<ffffffff81102ea0>] ? process_one_work+0x480/0x480
181.45  [ 37.864108] [<ffffffff81108d86>] kthread+0xd6/0xf0
181.46  [ 37.864108] [<ffffffff81108cb0>] ? kthread_create_on_node+0x180/0x180
181.47  [ 37.864108] [<ffffffff81aa690f>] ret_from_fork+0x3f/0x70
181.48  [ 37.864108] [<ffffffff81108cb0>] ? kthread_create_on_node+0x180/0x180
181.49  [ 37.864108] Code: 00 00 00 00 48 89 85 20 ff ff ff 48 8d 85 10 ff ff ff 8b 73 04 48 89 85 28 ff ff ff 49 8b 47 48 ff 50 28 85 c0 0f 88 5d 01 00 00 <49> 8b 44 24 08 48 85 c0 0f 84 3d 03 00 00 8b 00 89 85 08 ff ff
181.50  [ 37.864108] RIP [<ffffffffa01c41b7>] __event_probe__block_get_rq+0x127/0x4b0 [lttng_probe_block]
181.51  [ 37.864108] RSP <ffff88007c86ba98>
181.52  [ 37.864108] CR2: 0000000000000008

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>