Re: [PATCH] kfence: Avoid stalling work queue task without allocations

Marco Elver
2020-11-11T08:30:00Z

On Wed, 11 Nov 2020 at 00:23, Anders Roxell <anders.roxell@linaro.org> wrote:
[...]
>
> I gave them a spin on next-20201105 [1] and on next-20201110 [2].
>
> I eventually got to a prompt on next-20201105.
> However, I got to this kernel panic on the next-20201110:
>
> [...]
> [ 1514.089966][ T1] Testing event system initcall: OK
> [ 1514.806232][ T1] Running tests on all trace events:
> [ 1514.857835][ T1] Testing all events:
> [ 1525.503262][ C0] hrtimer: interrupt took 10902600 ns
> [ 1623.861452][ C0] BUG: workqueue lockup - pool cpus=0 node=0
> flags=0x0 nice=0 stuck for 65s!
> [...]
> [ 7823.104349][ T28] Tainted: G W
> 5.10.0-rc3-next-20201110-00008-g8dc06700529d #3
> [ 7833.206491][ T28] "echo 0 >
> /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 7840.750700][ T28] task:kworker/0:1 state:D stack:26640 pid:
> 1872 ppid: 2 flags:0x00000428
> [ 7875.642531][ T28] Workqueue: events toggle_allocation_gate
> [ 7889.178334][ T28] Call trace:
> [ 7897.066649][ T28] __switch_to+0x1cc/0x1e0
> [ 7905.326856][ T28] 0xffff00000f7077b0
> [ 7928.354644][ T28] INFO: lockdep is turned off.
> [ 7934.022572][ T28] Kernel panic - not syncing: hung_task: blocked tasks
> [ 7934.032039][ T28] CPU: 0 PID: 28 Comm: khungtaskd Tainted: G
> W 5.10.0-rc3-next-20201110-00008-g8dc06700529d #3
> [ 7934.045586][ T28] Hardware name: linux,dummy-virt (DT)
> [ 7934.053677][ T28] Call trace:
> [ 7934.060276][ T28] dump_backtrace+0x0/0x420
> [ 7934.067635][ T28] show_stack+0x38/0xa0
> [ 7934.091277][ T28] dump_stack+0x1d4/0x278
> [ 7934.098878][ T28] panic+0x304/0x5d8
> [ 7934.114923][ T28] check_hung_uninterruptible_tasks+0x5e4/0x640
> [ 7934.123823][ T28] watchdog+0x138/0x160
> [ 7934.131561][ T28] kthread+0x23c/0x260
> [ 7934.138590][ T28] ret_from_fork+0x10/0x18
> [ 7934.146631][ T28] Kernel Offset: disabled
> [ 7934.153749][ T28] CPU features: 0x0240002,20002004
> [ 7934.161476][ T28] Memory Limit: none
> [ 7934.171272][ T28] ---[ end Kernel panic - not syncing: hung_task:
> blocked tasks ]---
>
> Cheers,
> Anders
> [1] https://people.linaro.org/~anders.roxell/output-next-20201105-test.log
> [2] https://people.linaro.org/~anders.roxell/output-next-20201110-test.log

Thanks for testing. The fact that it passes on next-20201105 but not
on 20201110 is strange. If you boot with KFENCE disabled (boot param
kfence.sample_interval=0), does it boot?

In your log [2] I see a number of "BUG: workqueue lockup ..." but that
doesn't make sense, at least I don't think the KFENCE work item is
causing this. It'd be interesting to bisect what changed between
20201105 and 20201110, but I have a suspicion that might take too
long. Short of that, let me see if there are any changes between the 2
that look like it might be causing this.

Thanks,
-- Marco