Message-ID: <20251222082843.1816701-1-jim.cromie@gmail.com>
Date: Mon, 22 Dec 2025 21:28:12 +1300
From: Jim Cromie <jim.cromie@...il.com>
To: linux-kernel@...r.kernel.org,
	jbaron@...mai.com,
	gregkh@...uxfoundation.org,
	ukaszb@...omium.org,
	louis.chauvet@...tlin.com
Cc: dri-devel@...ts.freedesktop.org,
	amd-gfx@...ts.freedesktop.org,
	intel-gvt-dev@...ts.freedesktop.org,
	intel-gfx@...ts.freedesktop.org,
	daniel.vetter@...ll.ch,
	tvrtko.ursulin@...ux.intel.com,
	jani.nikula@...el.com,
	ville.syrjala@...ux.intel.com,
	seanpaul@...omium.org,
	robdclark@...il.com,
	groeck@...gle.com,
	yanivt@...gle.com,
	bleung@...gle.com,
	quic_saipraka@...cinc.com,
	will@...nel.org,
	catalin.marinas@....com,
	quic_psodagud@...cinc.com,
	maz@...nel.org,
	arnd@...db.de,
	linux-arm-kernel@...ts.infradead.org,
	linux-arm-msm@...r.kernel.org,
	mingo@...hat.com,
	jim.cromie@...il.com
Subject: [PATCH v7 00/31] drm/dyndbg: Fix dynamic debug classmap regression

hello all,

commit aad0214f3026 ("dyndbg: add DECLARE_DYNDBG_CLASSMAP macro")

added dyndbg's "classmaps" feature, which brought dyndbg's 0-off-cost
debug to DRM.  Dyndbg wired to /sys/module/drm/parameters/debug,
mapped its bits to classes named "DRM_UT_*", and effected the callsite
enablements only on updates to the sys-node (and underlying >control).

Sadly, it hit a CI failure, resulting in:
commit bb2ff6c27bc9 ("drm: Disable dynamic debug as broken")

The regression was that drivers, when modprobed, did not get the
drm.debug=0xff turn-on action, because that had already been done for
drm.ko itself.

The core design bug is in the DECLARE_DYNDBG_CLASSMAP macro.  Its use
in both drm.ko (ie core) and all drivers.ko meant that they couldn't
fundamentally distinguish their respective roles.  They each
"re-defined" the classmap separately, breaking K&R-101.

My ad-hoc test scripting helped to hide the error from me, by 1st
testing various combos of boot-time module.dyndbg=... and
drm.debug=... configurations, and then inadvertently relying upon
those initializations.

This series addresses both failings:

It replaces DECLARE_DYNDBG_CLASSMAP with

- `DYNAMIC_DEBUG_CLASSMAP_DEFINE`: Used by core modules (e.g.,
  `drm.ko`) to define their classmaps.  Based upon DECLARE, it exports
  the classmap so USE can use it.

- `DYNAMIC_DEBUG_CLASSMAP_USE`: this lets other "subsystem" users
  create a linkage to the classmap defined elsewhere (ie drm.ko).
  These users can then find their "parent" and apply its settings.

It adds a selftest script, and a 2nd "sub-module" to recapitulate
DRM's multi-module "subsystem" use-case, including the specific
failure scenario.

It also adds minor parsing enhancements, allowing easier construction
of multi-part debug configurations.  These enhancements are used to
test classmaps in particular, but are not otherwize required.

v7 adds:
. WARN_ONCE when classmap isnt found for a class'd callsite, JBaron
. reorder macro args to match kdoc, JBaron
. Doc formatting fixes, by Bagas

Thank you for your review.

P.S. Id also like to "tease" some other work:

1. patchset to send pr_debugs to tracefs on +T flag

   allows 63 "private" tracebufs, 1 "common" one (at 0)
   "drm.debug_2trace=0x1ff" is possible
   from Lukas Bartoski

2. patchset to save 40% of DATA_DATA footprint

   move (modname,filename,function) to struct _ddebug_site
   save their descriptor intervals to 3 maple-trees
   3 accessors fetch on descriptor, from trees
   move __dyndbg_sites __section to INIT_DATA

3. patchset to cache dynamic-prefixes
   should hide 2.s cost increase.


Jim Cromie (31):

fixes, cleanups, simple stuff::

Jim Cromie (31):
  dyndbg: factor ddebug_match_desc out from ddebug_change
  dyndbg: add stub macro for DECLARE_DYNDBG_CLASSMAP
  docs/dyndbg: update examples \012 to \n
  docs/dyndbg: explain flags parse 1st
  test-dyndbg: fixup CLASSMAP usage error
  dyndbg: reword "class unknown," to "class:_UNKNOWN_"
  dyndbg: make ddebug_class_param union members same size
  dyndbg: drop NUM_TYPE_ARRAY
  dyndbg: tweak pr_fmt to avoid expansion conflicts
  dyndbg: reduce verbose/debug clutter

callchain grooming, re-structs, code simplify/dedup by macros::

  dyndbg: refactor param_set_dyndbg_classes and below
  dyndbg: tighten fn-sig of ddebug_apply_class_bitmap
  dyndbg: replace classmap list with a vector
  dyndbg: macrofy a 2-index for-loop pattern
  dyndbg,module: make proper substructs in _ddebug_info
  dyndbg: hoist classmap-filter-by-modname up to ddebug_add_module
  dyndbg: move mod_name down from struct ddebug_table to _ddebug_info
  dyndbg-API: remove DD_CLASS_TYPE_(DISJOINT|LEVEL)_NAMES and code
  selftests-dyndbg: add a dynamic_debug run_tests target
  dyndbg: change __dynamic_func_call_cls* macros into expressions

core fix, detect api misuse errors, etc::

  dyndbg-API: replace DECLARE_DYNDBG_CLASSMAP
  dyndbg: detect class_id reservation conflicts
  dyndbg: check DYNAMIC_DEBUG_CLASSMAP_DEFINE args at compile-time
  dyndbg-test: change do_prints testpoint to accept a loopct
  dyndbg-API: promote DYNAMIC_DEBUG_CLASSMAP_PARAM to API
  dyndbg: treat comma as a token separator
  dyndbg: split multi-query strings with %
  selftests-dyndbg: add test_mod_submod
  dyndbg: resolve "protection" of class'd pr_debug
  dyndbg: add DYNAMIC_DEBUG_CLASSMAP_USE_(dd_class_name, offset)
  docs/dyndbg: add classmap info to howto

 .../admin-guide/dynamic-debug-howto.rst       | 187 ++++-
 MAINTAINERS                                   |   3 +-
 include/asm-generic/vmlinux.lds.h             |   5 +-
 include/linux/dynamic_debug.h                 | 302 +++++--
 kernel/module/main.c                          |  15 +-
 lib/Kconfig.debug                             |  24 +-
 lib/Makefile                                  |   5 +
 lib/dynamic_debug.c                           | 776 +++++++++++-------
 lib/test_dynamic_debug.c                      | 198 +++--
 lib/test_dynamic_debug_submod.c               |  21 +
 tools/testing/selftests/Makefile              |   1 +
 .../testing/selftests/dynamic_debug/Makefile  |   9 +
 tools/testing/selftests/dynamic_debug/config  |   7 +
 .../dynamic_debug/dyndbg_selftest.sh          | 373 +++++++++
 14 files changed, 1465 insertions(+), 461 deletions(-)
 create mode 100644 lib/test_dynamic_debug_submod.c
 create mode 100644 tools/testing/selftests/dynamic_debug/Makefile
 create mode 100644 tools/testing/selftests/dynamic_debug/config
 create mode 100755 tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh

-- 
2.52.0

Powered by blists - more mailing lists