Hi All,
On 2017-12-11 23:28, Javier Martinez Canillas wrote:
[adding Marek and Shuah to cc list]
On Mon, Dec 11, 2017 at 6:05 PM, Daniel Vetter daniel.vetter@ffwll.ch wrote:
On Mon, Dec 11, 2017 at 11:30 AM, Guillaume Tucker guillaume.tucker@collabora.com wrote:
Hi Daniel,
Please see below, I've had several bisection results pointing at that commit over the week-end on mainline but also on linux-next and net-next. While the peach-pi is a bit flaky at the moment and is likely to have more than one issue, it does seem like this commit is causing some well reproducible kernel hang.
Here's a re-run with v4.15-rc3 showing the issue:
https://lava.collabora.co.uk/scheduler/job/1018478
and here's another one with the change mentioned below reverted:
https://lava.collabora.co.uk/scheduler/job/1018479
They both show a warning about "unbalanced disables for lcd_vdd", I don't know if this is related as I haven't investigated any further. It does appear to reliably hang with v4.15-rc3 and boot most of the time with the commit reverted though.
The automated kernelci.org bisection is still an experimental tool and it may well be a false positive, so please take this result with a pinch of salt...
The patch just very minimal moves the connector cleanup around (so timing change), but except when you unload a driver (or maybe that funny EPROBE_DEFER stuff) it shouldn't matter. So if you don't have more info than "seems to hang a bit more" I have no idea what's wrong. The patch itself should work, at least it survived quite some serious testing we do on everything. -Daniel
Marek was pointing to a different culprit [0] in this [1] thread. I see that both commits made it to v4.15-rc3, which is the first version where boot fails. So maybe is a combination of both? Or rather reverting one patch masks the error in the other.
I've access to the machine but unfortunately not a lot of time to dig on this, I could try to do it in the weekend though.
After a recent discussion on the Javier's patch: https://patchwork.kernel.org/patch/10106417/ I've managed to reproduce this issue also on Exynos5250 based Samsung Snow Chromebook and investigate a bit.
It is caused by a deadlock in the main kernel workqueue. Here are details:
1. Exynos DRM fails to initialize due to missing regulators and gets moved to deferred probe device list
2. Deferred probe is triggered and kernel "events" workqueue calls deferred_probe_work_func()
3. exynos_drm_bind() is called, component_bind_all() fails due to missing Exynos Mixer device
4. error handling path is executed in exynos_drm_bind(), which calls drm_mode_config_cleanup()
5. drm_mode_config_cleanup() calls flush_scheduled_work(), what causes deadlock.
Do You have idea how to fix this issue properly?
Taking a look at git blame, this indeed shows that the issue has been introduced by the commit a703c55004e1 ("drm: safely free connectors from connector_ite"), which added a call to flush_scheduled_work() in drm_mode_config_cleanup().
drm_mode_config_cleanup() should avoid calling flush_scheduled_work() if called from the workqueue, but I don't have idea how to check that. The other way of fixing it would be to resurrect separate workqueue for DRM related events.
Best regards