Re: d57108d4f6 ("watchdog/core: Get rid of the thread .."): BUG: unable to handle kernel NULL pointer dereference at 0000000000000208

[Thomas Gleixner]

On Fri, 15 Sep 2017, kernel test robot wrote:
> [    0.035023] CPU: Intel Common KVM processor (family: 0xf, model: 0x6, stepping: 0x1)
> [    0.042302] Performance Events: unsupported Netburst CPU model 6 no PMU driver, software events only.

Cute. So there is no supported PMU, but for some unknown reason the lockup
detector can create an event, otherwise the perf availaibility check in
lockup_detector_init() would fail ....

Peter???

> [    0.051650] BUG: unable to handle kernel NULL pointer dereference at 0000000000000208
> [    0.052000] IP: perf_event_release_kernel+0x14/0x1ed
> [    0.052000] PGD 0 P4D 0 
> [    0.052000] Oops: 0000 [#1]
> [    0.052000] CPU: 0 PID: 1 Comm: swapper Not tainted 4.13.0-11828-gd57108d #1
> [    0.052000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-20161025_171302-gandalf 04/01/2014
> [    0.052000] task: ffff88001e532000 task.stack: ffffc90000008000
> [    0.052000] RIP: 0010:perf_event_release_kernel+0x14/0x1ed
> [    0.052000] RSP: 0000:ffffc9000000be38 EFLAGS: 00010292
> [    0.052000] RAX: 0000000000000001 RBX: 0000000000000000 RCX: 000000000313fa45
> [    0.052000] RDX: 0000000000000001 RSI: ffffffff828265e0 RDI: 0000000000000000
> [    0.052000] RBP: ffffc9000000beb8 R08: ffffc9000000bdc8 R09: 0000000000000000
> [    0.052000] R10: ffff88001e532000 R11: ffffc9000000bd68 R12: 0000000000000000
> [    0.052000] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> [    0.052000] FS:  0000000000000000(0000) GS:ffffffff8262f000(0000) knlGS:0000000000000000
> [    0.052000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    0.052000] CR2: 0000000000000208 CR3: 0000000002618000 CR4: 00000000000006b0
> [    0.052000] Call Trace:
> [    0.052000]  ? trace_hardirqs_on_caller+0x162/0x198
> [    0.052000]  hardlockup_detector_perf_cleanup+0x20/0x2d
> [    0.052000]  __lockup_detector_cleanup+0x2c/0x2e
> [    0.052000]  softlockup_update_smpboot_threads+0x48/0x4a
> [    0.052000]  softlockup_reconfigure_threads+0x21/0x5a
> [    0.052000]  lockup_detector_init+0x75/0x83
> [    0.052000]  kernel_init_freeable+0x67/0xf0
> [    0.052000]  ? rest_init+0x13a/0x13a
> [    0.052000]  kernel_init+0xe/0xf8
> [    0.052000]  ret_from_fork+0x2a/0x40
> [    0.052000] Code: df e8 0c b2 ff ff 4c 89 e7 e8 89 13 bd 00 41 5b 5b 41 5c 41 5d c9 c3 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 89 fb 48 83 ec 58 <48> 83 bf 08 02 00 00 00 75 14 f6 87 8c 00 00 00 03 0f 84 9b 01 
> [    0.052000] RIP: perf_event_release_kernel+0x14/0x1ed RSP: ffffc9000000be38
> [    0.052000] CR2: 0000000000000208
> [    0.052000] ---[ end trace ed0d2c92e47d08db ]---
> [    0.052000] Kernel panic - not syncing: Fatal exception