Re: [PATCH 00/63] Fix CONFIG_DRM_USE_DYNAMIC_DEBUG=y

[Simona Vetter <simona.vetter@ffwll.ch>]

On Thu, Feb 20, 2025 at 09:31:41AM +0100, Greg KH wrote:
> On Fri, Jan 24, 2025 at 11:45:14PM -0700, Jim Cromie wrote:
> > This series fixes dynamic-debug's support for DRM debug-categories.
> > Classmaps-v1 evaded full review, and got committed in 2 chunks:
> > 
> >   b7b4eebdba7b..6ea3bf466ac6	# core dyndbg changes
> >   0406faf25fb1..ee7d633f2dfb	# drm adoption
> > 
> > DRM-CI found a regression during init with drm.debug=<initval>; the
> > static-keys under the drm-dbgs in drm.ko got enabled, but those in
> > drivers & helpers did not.
> > 
> > Root Problem:
> > 
> > DECLARE_DYNDBG_CLASSMAP violated a K&R rule "define once, refer
> > afterwards".  Replace it with DYNDBG_CLASSMAP_DEFINE (invoked once in
> > drm-core) and DYNDBG_CLASSMAP_USE (invoked repeatedly, in drivers &
> > helpers).
> > 
> > _DEFINE exports the classmap it creates (in drm.ko), other modules
> > _USE the classmap.  The _USE adds a record ref'g the _DEFINEd (&
> > exported) classmap, in a 2nd __dyndbg_class_users section.
> > 
> > So now at modprobe, dyndbg scans the new section after the 1st
> > __dyndbg_class_maps section, follows the linkage to the _DEFINEr
> > module, finds the (optional) kernel-param controlling the classmap,
> > examines its drm.debug=<initval>, and applies it to the module being
> > initialized.
> > 
> > To recapitulate the multi-module problem wo DRM involvement, Add:
> > 
> > A. tools/testing/selftests/dynamic_debug/*
> > 
> > This alters pr_debugs in the test-modules, counts the results and
> > checks them against expectations.  It uses this formula to test most
> > of the control grammar, including the new class keyword.
> > 
> > B. test_dynamic_debug_submod.ko
> > 
> > This alters the test-module to build both parent & _submod ko's, with
> > _DEFINE and _USE inside #if/#else blocks.  This recap's DRM's 2 module
> > failure scenario, allowing A to exersize several cases.
> > 
> > The #if/#else puts the 2 macro uses together for clarity, and gives
> > the 2 modules identical sets of debugs.
> > 
> > Recent DRM-CI tests are here:
> >   https://patchwork.freedesktop.org/series/139147/
> > 
> > Previous rev:
> >   https://lore.kernel.org/lkml/20240716185806.1572048-1-jim.cromie@gmail.com/
> > 
> > Noteworthy Additions:
> > 
> > 1- drop class "protection" special case, per JBaron's preference.
> >    only current use is marked BROKEN so nobody to affect.
> >    now framed as policy-choice:
> >    #define ddebug_client_module_protects_classes() false
> >    subsystems wanting protection can change this.
> > 
> > 2- compile-time arg-tests in DYNDBG_CLASSMAP_DEFINE
> >    implement several required constraints, and fail obviously.
> > 
> > 3- modprobe time check of conflicting class-id reservations
> >    only affects 2+classmaps users.
> >    compile-time solution not apparent.
> > 
> > 4- dyndbg can now cause modprobe to fail.
> >    needed to catch 3.
> >    maybe some loose ends here on failure.
> > 
> > 5- refactor & rename ddebug_attach_*module_classes
> >    reduce repetetive boilerplate on 2 types: maps, users.
> >    rework mostly brought forward in patchset to reduce churn
> >    TBD: maybe squash more.
> > 
> > Several recent trybot submissions (against drm-tip) have been passing
> > CI.BAT, and failing one or few CI.IGT tests randomly; re-tests do not
> > reliably repeat the failures.
> > 
> > its also at github.com:jimc/linux.git
> >   dd-fix-9[st]-ontip  &  dd-fix-9-13
> > 
> > Ive been running it on my desktop w/o issues.
> > 
> > The drivers/gpu/drm patches are RFC, I think there might be a single
> > place to call DRM_CLASSMAP_USE(drm_dedbug_classes) to replace the
> > sprinkling of _USEs in drivers and helpers.  IIRC, I tried adding a
> > _DEFINE into drm_drv.c, that didn't do it, so I punted for now.
> > 
> > I think the dyndbg core additions are ready for review and merging
> > into a (next-next) test/integration tree.
> 
> So whose tree should this go through?

I'm trying to get some drm folks to review/test this, but thus far not
much success :-/ I think it's good stuff, but I'm somewhat hesitant if no
one else agrees that it's useful for CI or in-field crash-recording or
whatever ...

I guess worst case we can land it and hope it attracts more folks?

Wrt tree I don't care, but I guess we should then also land the drm side
too.
-Sima

> And I think the last patch in this series isn't correct, it looks like a
> 000 email somehow.
> 
> thanks,
> 
> greg k-h

-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch