Re: [RFC][PATCH 00/21] tracing: Inter-event (e.g. latency) support

[Tom Zanussi]

Hi Steve,

On Wed, 2017-02-08 at 15:01 -0500, Steven Rostedt wrote:
> On Wed,  8 Feb 2017 11:24:56 -0600
> Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> wrote:
> 
> >     # echo 'wakeup_latency lat=sched_switch:wakeup_lat \
> >                            pid=sched_switch:woken_pid \
> >                            prio=sched_switch:woken_prio' >> \
> >             /sys/kernel/debug/tracing/synthetic_events
> 
> I applied all your patches, did the above and then:
> 
>  BUG: unable to handle kernel NULL pointer dereference at 0000000000000034
>  IP: free_synthetic_event+0x46/0xb0
>  PGD 0 
>  
>  Oops: 0000 [#1] SMP
>  Modules linked in: ip6table_filter ip6_tables x86_pkg_temp_thermal kvm_intel kvm snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core irqbypass snd_seq snd_seq_device snd_pcm snd_timer snd i2c_i801 soundcore wmi i915 i2c_algo_bit drm_kms_helper e1000e syscopyarea sysfillrect sysimgblt fb_sys_fops ptp drm pps_core i2c_core video
>  CPU: 0 PID: 1389 Comm: bash Not tainted 4.10.0-rc2-test+ #36
>  Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v02.05 05/07/2012
>  task: ffff8800c8c48000 task.stack: ffffc90000a00000
>  RIP: 0010:free_synthetic_event+0x46/0xb0
>  RSP: 0018:ffffc90000a03cf8 EFLAGS: 00010282
>  RAX: 0000000015675b00 RBX: ffff8800ccf4bcd0 RCX: 0000000000000000
>  RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>  RBP: ffffc90000a03d18 R08: 0000000000000000 R09: ffff8800ccea7c6c
>  R10: 000000000000003d R11: ffff8800c8c48000 R12: 0000000000000001
>  R13: ffff8800c8ca6000 R14: ffff8800ccea7d88 R15: 0000000000000001
>  FS:  00007fde7acdb700(0000) GS:ffff88011ea00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000034 CR3: 00000000ccc44000 CR4: 00000000001406f0
>  Call Trace:
>   create_synthetic_event+0xcb/0x580
>   ? parse_var_ref+0x120/0x120
>   trace_run_command+0x5f/0x70
>   trace_parse_run_command+0x76/0x150
>   ? parse_var_ref+0x120/0x120
>   synthetic_events_write+0x10/0x20
>   __vfs_write+0x28/0x140
>   ? vmacache_find+0xcc/0x180
>   ? rw_verify_area+0xd8/0x190
>   ? _cond_resched+0x2e/0x50
>   ? __sb_start_write+0x82/0xe0
>   vfs_write+0x138/0x260
>   SyS_write+0x4f/0xa0
>   entry_SYSCALL_64_fastpath+0x13/0x94
> 

Hmm, ok, I'm not seeing it here, but I'll take a deeper look and see
what could be going on there.

> 
> Anyway, I kinda like the approach. I'll go patch by patch to see what
> you did and maybe even take a few now, if they seem appropriate as
> helpers.
> 

OK, great, thanks!

Tom

> -- Steve