Re: [Intel-gfx] ✗ Fi.CI.BAT: failure for drm/i915: implement internal workqueues (rev3)

["Coelho, Luciano" <luciano.coelho@intel.com>]

On Tue, 2023-06-06 at 11:06 +0100, Tvrtko Ursulin wrote:
> On 05/06/2023 16:06, Jani Nikula wrote:
> > On Wed, 31 May 2023, Patchwork <patchwork@emeril.freedesktop.org> wrote:
> > > #### Possible regressions ####
> > > 
> > >    * igt@gem_close_race@basic-process:
> > >      - fi-blb-e6850:       [PASS][1] -> [ABORT][2]
> > >     [1]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_13203/fi-blb-e6850/igt@gem_close_race@basic-process.html
> > >     [2]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_117618v3/fi-blb-e6850/igt@gem_close_race@basic-process.html
> > >      - fi-hsw-4770:        [PASS][3] -> [ABORT][4]
> > >     [3]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_13203/fi-hsw-4770/igt@gem_close_race@basic-process.html
> > >     [4]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_117618v3/fi-hsw-4770/igt@gem_close_race@basic-process.html
> > >      - fi-elk-e7500:       [PASS][5] -> [ABORT][6]
> > >     [5]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_13203/fi-elk-e7500/igt@gem_close_race@basic-process.html
> > >     [6]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_117618v3/fi-elk-e7500/igt@gem_close_race@basic-process.html
> > > 
> > >    * igt@i915_selftest@live@evict:
> > >      - bat-adlp-9:         [PASS][7] -> [ABORT][8]
> > >     [7]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_13203/bat-adlp-9/igt@i915_selftest@live@evict.html
> > >     [8]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_117618v3/bat-adlp-9/igt@i915_selftest@live@evict.html
> > >      - bat-rpls-2:         [PASS][9] -> [ABORT][10]
> > >     [9]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_13203/bat-rpls-2/igt@i915_selftest@live@evict.html
> > >     [10]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_117618v3/bat-rpls-2/igt@i915_selftest@live@evict.html
> > >      - bat-adlm-1:         [PASS][11] -> [ABORT][12]
> > >     [11]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_13203/bat-adlm-1/igt@i915_selftest@live@evict.html
> > >     [12]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_117618v3/bat-adlm-1/igt@i915_selftest@live@evict.html
> > >      - bat-rpls-1:         [PASS][13] -> [ABORT][14]
> > >     [13]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_13203/bat-rpls-1/igt@i915_selftest@live@evict.html
> > >     [14]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_117618v3/bat-rpls-1/igt@i915_selftest@live@evict.html
> > 
> > This still fails consistently, I have no clue why, and the above aren't
> > even remotely related to display.
> > 
> > What now? Tvrtko?
> 
> Hmm..
> 
> <4> [46.782321] Chain exists of:
>    (wq_completion)i915 --> (work_completion)(&i915->mm.free_work) --> &vm->mutex
> <4> [46.782329]  Possible unsafe locking scenario:
> <4> [46.782332]        CPU0                    CPU1
> <4> [46.782334]        ----                    ----
> <4> [46.782337]   lock(&vm->mutex);
> <4> [46.782340]                                lock((work_completion)(&i915->mm.free_work));
> <4> [46.782344]                                lock(&vm->mutex);
> <4> [46.782348]   lock((wq_completion)i915);
> 
> 
> "(wq_completion)i915"
> 
> So it's not about the new wq even. Perhaps it is this hunk:
> 
> --- a/drivers/gpu/drm/i915/intel_wakeref.c
> +++ b/drivers/gpu/drm/i915/intel_wakeref.c
> @@ -75,7 +75,7 @@ void __intel_wakeref_put_last(struct intel_wakeref *wf, unsigned long flags)
>   
>   	/* Assume we are not in process context and so cannot sleep. */
>   	if (flags & INTEL_WAKEREF_PUT_ASYNC || !mutex_trylock(&wf->mutex)) {
> -		mod_delayed_work(system_wq, &wf->work,
> +		mod_delayed_work(wf->i915->wq, &wf->work,
> 
> Transformation from this patch otherwise is system_wq with the new unordered wq, so I'd try that first.

Indeed this seems to be exactly the block that is causing the issue.  I
was sort of bisecting through all these changes and reverting this one
prevents the lockdep splat from happening...

So there's something that needs to be synced with the system_wq here,
but what? I need to dig into it.

--
Cheers,
Luca.