hv: clocksource: Add notrace attribute to read_hv_sched_clock_*() functions

When selecting function_graph tracer with the command:
 # echo function_graph > /sys/kernel/debug/tracing/current_tracer

The kernel crashes with the following stack trace:

[69703.122389] BUG: stack guard page was hit at 000000001056545c (stack is 00000000fa3f8fed..0000000005d39503)
[69703.122403] kernel stack overflow (double-fault): 0000 [#1] SMP PTI
[69703.122413] CPU: 0 PID: 16982 Comm: bash Kdump: loaded Not tainted 4.18.0-236.el8.x86_64 #1
[69703.122420] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.0 12/17/2019
[69703.122433] RIP: 0010repare_ftrace_return+0xa/0x110
[69703.122458] Code: 05 00 0f 0b 48 c7 c7 10 ca 69 ae 0f b6 f0 e8 4b 52 0c 00 31 c0 eb ca 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 56 41 55 41 54 <53> 48 83 ec 18 65 48 8b 04 25 28 00 00 00 48 89 45 d8 31 c0 48 85
[69703.122467] RSP: 0018:ffffbd6d01118000 EFLAGS: 00010086
[69703.122476] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000003
[69703.122484] RDX: 0000000000000000 RSI: ffffbd6d011180d8 RDI: ffffffffadce7550
[69703.122491] RBP: ffffbd6d01118018 R08: 0000000000000000 R09: ffff9d4b09266000
[69703.122498] R10: ffff9d4b0fc04540 R11: ffff9d4b0fc20a00 R12: ffff9d4b6e42aa90
[69703.122506] R13: ffff9d4b0fc20ab8 R14: 00000000000003e8 R15: ffffbd6d0111837c
[69703.122514] FS:  00007fd5f2588740(0000) GS:ffff9d4b6e400000(0000) knlGS:0000000000000000
[69703.122521] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[69703.122528] CR2: ffffbd6d01117ff8 CR3: 00000000565d8001 CR4: 00000000003606f0
[69703.122538] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[69703.122545] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[69703.122552] Call Trace:
[69703.122568]  ftrace_graph_caller+0x6b/0xa0
[69703.122589]  ? read_hv_sched_clock_tsc+0x5/0x20
[69703.122599]  read_hv_sched_clock_tsc+0x5/0x20
[69703.122611]  sched_clock+0x5/0x10
[69703.122621]  sched_clock_local+0x12/0x80
[69703.122631]  sched_clock_cpu+0x8c/0xb0
[69703.122644]  trace_clock_global+0x21/0x90
[69703.122655]  ring_buffer_lock_reserve+0x100/0x3c0
[69703.122671]  trace_buffer_lock_reserve+0x16/0x50
[69703.122683]  __trace_graph_entry+0x28/0x90
[69703.122695]  trace_graph_entry+0xfd/0x1a0
[69703.122705]  ? read_hv_clock_tsc_cs+0x10/0x10
[69703.122714]  ? sched_clock+0x5/0x10
[69703.122723]  prepare_ftrace_return+0x99/0x110
[69703.122734]  ? read_hv_clock_tsc_cs+0x10/0x10
[69703.122743]  ? sched_clock+0x5/0x10
[69703.122752]  ftrace_graph_caller+0x6b/0xa0
[69703.122768]  ? read_hv_clock_tsc_cs+0x10/0x10
[69703.122777]  ? sched_clock+0x5/0x10
[69703.122786]  ? read_hv_sched_clock_tsc+0x5/0x20
[69703.122796]  ? ring_buffer_unlock_commit+0x1d/0xa0
[69703.122805]  read_hv_sched_clock_tsc+0x5/0x20
[69703.122814]  ftrace_graph_caller+0xa0/0xa0
[ ... recursion snipped ... ]

Setting the notrace attribute for read_hv_sched_clock_msr() and
read_hv_sched_clock_tsc() fixes it.

Fixes: bd00cd52 ("clocksource/drivers/hyperv: Add Hyper-V specific sched clock function")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
Link: https://lore.kernel.org/r/20200924151117.767442-1-mgamal@redhat.com


Signed-off-by: Wei Liu <wei.liu@kernel.org>