Hi,

Somewhere in the 3.1 cycle - haven't yet bisected - I started to get
somewhat reprodcable crashes after using perf.
There is no direct correlation with a concrete action via perf I can
see so far but without having used perf the system runs stable.

[  673.145686] BUG: unable to handle kernel NULL pointer dereference at 0000000000000048
[  673.145806] IP: [<ffffffff810e6ef9>] perf_ctx_adjust_freq+0x49/0x100
[  673.145864] PGD 0
[  673.145907] Oops: 0000 [#1] SMP
[  673.145953] CPU 4
[  673.145969] Modules linked in: iptable_filter ip_tables x_tables snd_hda_codec_ca0110 snd_hda_codec_hdmi snd_hda_intel snd_hda_codec snd_pcm_oss snd_hwdep snd_mixer_oss snd_pcm snd_seq_oss snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device snd_timer snd snd_page_alloc [last unloaded: scsi_wait_scan]
[  673.146246]
[  673.146261] Pid: 0, comm: kworker/0:1 Not tainted 3.1.0-andres #113 empty empty/S7020
[  673.146321] RIP: 0010:[<ffffffff810e6ef9>]  [<ffffffff810e6ef9>] perf_ctx_adjust_freq+0x49/0x100
[  673.146380] RSP: 0018:ffff88063fc03d98  EFLAGS: 00010082
[  673.146414] RAX: 0000000000000000 RBX: fffffffffffffff0 RCX: 000000000000038f
[  673.146456] RDX: 0000000000000004 RSI: 000000000032dbfc RDI: ffff880327cc2780
[  673.146499] RBP: ffff88063fc03dc8 R08: 0000000000000000 R09: 0000000000000020
[  673.146542] R10: 0000000000000001 R11: 0000000000000000 R12: ffff880327cc27d0
[  673.146586] R13: 000000000032dbfc R14: ffff88063fc0e4d0 R15: ffff880327cc2780
[  673.146628] FS:  0000000000000000(0000) GS:ffff88063fc00000(0000) knlGS:0000000000000000
[  673.146676] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  673.146712] CR2: 0000000000000048 CR3: 0000000002006000 CR4: 00000000000006e0
[  673.146753] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  673.146795] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  673.146838] Process kworker/0:1 (pid: 0, threadinfo ffff88032bf30000, task ffff88032bf2dc40)
[  673.146886] Stack:
[  673.146902]  ffff88062a65d000 0000000000000000 ffff88063fc03dc8 ffff88063fc15638
[  673.146967]  ffff88063fc0e400 ffff88063fc15708 ffff88063fc03e18 ffffffff810e701d
[  673.147033]  000000000032dbfc 0000000000000000 0000000000011f40 ffff88063fc11f40
[  673.147095] Call Trace:
[  673.147114]  <IRQ>
[  673.147138]  [<ffffffff810e701d>] perf_event_task_tick+0x6d/0x2a0
[  673.147180]  [<ffffffff8104ceab>] scheduler_tick+0xdb/0x280
[  673.147219]  [<ffffffff81066a4e>] update_process_times+0x6e/0x90
[  673.147261]  [<ffffffff81089414>] tick_sched_timer+0x64/0xc0
[  673.147301]  [<ffffffff8107ba7a>] __run_hrtimer+0x6a/0x220
[  673.147338]  [<ffffffff810893b0>] ? tick_nohz_handler+0x100/0x100
[  673.147378]  [<ffffffff8107c65b>] hrtimer_interrupt+0xeb/0x200
[  673.147419]  [<ffffffff819f4b19>] smp_apic_timer_interrupt+0x69/0x99
[  673.147463]  [<ffffffff819f2bb0>] apic_timer_interrupt+0x70/0x80
[  673.147500]  <EOI>
[  673.147523]  [<ffffffff819edefd>] ? notifier_call_chain+0x4d/0x70
[  673.147567]  [<ffffffff8151010f>] ? intel_idle+0xdf/0x130
[  673.147602]  [<ffffffff81510108>] ? intel_idle+0xd8/0x130
[  673.147643]  [<ffffffff81874a40>] cpuidle_idle_call+0xc0/0x1d0
[  673.147684]  [<ffffffff810008ff>] cpu_idle+0xcf/0x120
[  673.147722]  [<ffffffff819d6124>] start_secondary+0x1f0/0x1f7
[  673.147758] Code: 45 d8 48 8d 58 f0 49 39 c4 75 20 e9 a2 00 00 00 66 90 48 8b 43 10 48 89 45 d8 48 8b 45 d8 48 8d 58 f0 49 39 c4 0f 84 87 00 00 00
[  673.148094]  7b 58 01 75 e1 8b 83 ec 01 00 00 83 f8 ff 74 0c 65 8b 14 25
[  673.148265] RIP  [<ffffffff810e6ef9>] perf_ctx_adjust_freq+0x49/0x100
[  673.148312]  RSP <ffff88063fc03d98>
[  673.148336] CR2: 0000000000000048

Unless I did something wrong perf_ctx_adjust_freq+0x49/0x100 is
v3.1:kernel/events/core.c:2325.

Any other information I can give, kernel version or such I should
test?

Greetings,

Andres