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SubjectRe: [patch V2 22/29] lockup_detector: Make watchdog_nmi_reconfigure() two stage
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Thomas Gleixner <tglx@linutronix.de> writes:

> On Tue, 3 Oct 2017, Thomas Gleixner wrote:
>> On Tue, 3 Oct 2017, Thomas Gleixner wrote:
>> > On Tue, 3 Oct 2017, Michael Ellerman wrote:
>> > > Hmm, I tried that patch, it makes the warning go away. But then I
>> > > triggered a deliberate hard lockup and got nothing.
>> > >
>> > > Then I went back to the existing code (in linux-next), and I still get
>> > > no warning from a deliberate hard lockup.
>> > >
>> > > So seems there may be some more gremlins. Will test more in the morning.
>> >
>> > Hrm. That's weird. I'll have a look and send a proper patch series on top
>> > of next.
>>
>> The major difference is that the reworked code utilizes
>> watchdog_nmi_reconfigure() for both init and the sysctl updates, but I
>> can't for my life figure out why that doesn't work.
>
> I collected the changes which Linus requested along with the nmi_probe()
> one and pushed them into:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.core/urgent
>
> That's based on 4.13 final so it neither contains 4.14 nor -next material.

Thanks. I tested that here and it seems fine. The warning at boot is
gone and it is correctly catching a hard lockup triggered via LKDTM, eg:

# mount -t debugfs none /sys/kernel/debug
# echo HARDLOCKUP > /sys/kernel/debug/provoke-crash/DIRECT
lkdtm: Performing direct entry HARDLOCKUP
Watchdog CPU:0 Hard LOCKUP
Modules linked in:
CPU: 0 PID: 1215 Comm: sh Not tainted 4.13.0-gcc6-11846-g86be5ee #162
task: c0000000f1fc4c00 task.stack: c0000000ee3ac000
NIP: c0000000007205a4 LR: c00000000071f950 CTR: c000000000720570
REGS: c00000003ffffd80 TRAP: 0900 Not tainted (4.13.0-gcc6-11846-g86be5ee)
MSR: 9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE> CR: 28002228 XER: 00000000
CFAR: c0000000007205a8 SOFTE: 0
GPR00: c00000000071f950 c0000000ee3afbb0 c00000000107cf00 c0000000010604f0
GPR04: c0000000ffa05d90 c0000000ffa1c968 0000000000000000 0000000000000000
GPR08: 0000000000000007 0000000000000001 0000000000000000 9000000030001003
GPR12: c000000000720570 c00000000fd40000 0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000000 00000000100b8fd0
GPR20: 000001002f5a3485 00000000100b8f90 0000000000000000 0000000000000000
GPR24: c000000001060778 c0000000ee3afe00 c0000000ee3afe00 c0000000010603b0
GPR28: 000000000000000b c0000000f1fe0000 0000000000000140 c0000000010604f0
NIP [c0000000007205a4] lkdtm_HARDLOCKUP+0x34/0x40
LR [c00000000071f950] lkdtm_do_action+0x50/0x70
Call Trace:
[c0000000ee3afbb0] [0000000000000140] 0x140 (unreliable)
[c0000000ee3afbd0] [c00000000071f950] lkdtm_do_action+0x50/0x70
[c0000000ee3afc00] [c00000000071fdc0] direct_entry+0x110/0x1b0
[c0000000ee3afc90] [c00000000050141c] full_proxy_write+0x9c/0x110
[c0000000ee3afcf0] [c000000000336a3c] __vfs_write+0x6c/0x210
[c0000000ee3afd90] [c000000000338960] vfs_write+0xd0/0x270
[c0000000ee3afde0] [c00000000033a93c] SyS_write+0x6c/0x110
[c0000000ee3afe30] [c00000000000b220] system_call+0x58/0x6c
Instruction dump:
3842c990 7c0802a6 f8010010 f821ffe1 60000000 60000000 39400000 892d027a
994d027a 60000000 60420000 7c210b78 <7c421378> 4bfffff8 60420000 3c4c0096
Kernel panic - not syncing: Hard LOCKUP

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers

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