Re: [PATCH RESEND] hv: clocksource: Add notrace attribute to read_hv_sched_clock_*() functions

[Mohammed Gamal <mgamal@redhat.com>]

On Mon, 2020-10-05 at 13:47 +0200, Mohammed Gamal wrote:
> 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
> [...]
> 
> Setting the notrace attribute for read_hv_sched_clock_msr() and
> read_hv_sched_clock_tsc() fixes it
> 
> Fixes: bd00cd52d5be ("clocksource/drivers/hyperv: Add Hyper-V
> specific
> sched clock function")
> Suggested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
> ---
>  drivers/clocksource/hyperv_timer.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clocksource/hyperv_timer.c
> b/drivers/clocksource/hyperv_timer.c
> index 09aa44cb8a91d..ba04cb381cd3f 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -341,7 +341,7 @@ static u64 notrace read_hv_clock_tsc_cs(struct
> clocksource *arg)
>  	return read_hv_clock_tsc();
>  }
>  
> -static u64 read_hv_sched_clock_tsc(void)
> +static u64 notrace read_hv_sched_clock_tsc(void)
>  {
>  	return (read_hv_clock_tsc() - hv_sched_clock_offset) *
>  		(NSEC_PER_SEC / HV_CLOCK_HZ);
> @@ -404,7 +404,7 @@ static u64 notrace read_hv_clock_msr_cs(struct
> clocksource *arg)
>  	return read_hv_clock_msr();
>  }
>  
> -static u64 read_hv_sched_clock_msr(void)
> +static u64 notrace read_hv_sched_clock_msr(void)
>  {
>  	return (read_hv_clock_msr() - hv_sched_clock_offset) *
>  		(NSEC_PER_SEC / HV_CLOCK_HZ);

Please ignore the patch. Somehow I missed Wei's reply on it. It's
already applied to hyperv-next.

Thanks