[PATCH v8 00/35] fix CONFIG_DRM_USE_DYNAMIC_DEBUG=y regression

[Jim Cromie <jim.cromie@gmail.com>]

hi Greg, Jason, DRM-folk,

This patchset fixes the CONFIG_DRM_USE_DYNAMIC_DEBUG=y regression,
Fixes: bb2ff6c27bc9 ("drm: Disable dynamic debug as broken")

this is v8.
Its also here:
https://github.com/jimc/linux/tree/dd-classmap-fix-8a

v7 had at least 2 problems:

 https://lore.kernel.org/lkml/20231101002609.3533731-1-jim.cromie@gmail.com/
 https://patchwork.freedesktop.org/series/125066/

1. missing __align(8) in METATDATA macro, giving too much placement
freedom to linker, caused weird segvs following non-ptr vals, but for
builtin modules only. found by lkp-test.

2. the main patch changed both the dyndbg API, and the drm/drivers.
This was a flag-day annoyance, and not practical.  Fix by preserving
old API macro until "later", and splitting the patch and set into 2
sequential subsets.  removal can wait.
 
What was broken ?

Booting a modular kernel with drm.debug=0x1ff, this enabled pr_debugs
only in drm itself, not the yet-to-be loaded driver + helpers.  I had
tested with scripts doing lots of modprobes with dyndbg=<> options
permuting.  I didn't notice that I didn't really test without them.

The deeper cause was my design error, a violation of the K&R rule:
"define once, refer many times".

DECLARE_DYNDBG_CLASSMAP defined the classmap, and was used everywhere,
re-declaring the same static classmap repeatedly. Jani Nikula actually
picked up on this at the time, but didn't scream loudly enough for
anyone to notice, I know I didn't get it then.  One patchset across 2
trees didn't help either.

The revised classmap API "splits" it to def & ref.

DYNDBG_CLASSMAP_DEFINE fixes & updates the busted macro, EXPORTing the
classmap instead.  It gets invoked once per subsystem, by the
parent/builtin, drm.ko for DRM.

DYNDBG_CLASSMAP_USE in drivers and helpers refer to the classmap by
name, which links the 2 modules (like __drm_debug already does).

These 2 tell dyndbg to map "class FOO" to the defined FOO_ID, which
allows it to make those changes via >control.

DYNDBG_CLASSMAP_PARAM*, defines the controlling kparam, and binds it
to both the _var, and the _DEFINEd classmap.  So drm uses this to bind
the classmap to __drm_debug.

It provides the common control-point for the sub-system; it is applied
to the classmaps during modprobe of both _DEFINEr and USErs.  It also
enforces the relative nature of LEVEL classmaps, ie V3>V2.

DECLARE_DYNDBG_CLASSMAP is preserved to decouple the DRM patches.

A new struct and elf section contain the _USEs; on modprobe, these are
scanned similarly to the _DEFINEs, but follow the references to their
defining modules, find the kparam wired to the classmap, and apply its
classmap settings to the USEr.  This action is what V1 missed, which
is why drivers failed to enable debug during modprobe.

In order to recapitulate the regression scenario without involving
DRM, the patchset (v6 I think) adds test_dynamic_debug_submod, which
is a duplicate of its parent; _submod.c #defines _SUBMOD, and then
includes parent.

This puts _DEFINE and _USE close together in the same file, for
obviousness.  It also guarantees that the submod always has the same
complement of debug()s, giving consistent output from both when
classmaps are working properly, as tested when changing callsites via
both param and >control.

To provide a turn-key selftest, the patchset also adds
./tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh, pilfered
from a debug-to-trace patchset I and Lukasz Bartozik have been working
out.  It starts with basic_tests, then to test 2 new parsing
delimiters, which simplify testing of the classmap functionality.

It works nicely from virtme-ng:

[jimc@frodo vx]$ vrun_ -- ./tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh
doing: vng --verbose --name v6.9-rc5-34-g2f1ace6e1c68 \
       --user root --cwd ../.. \
       -a dynamic_debug.verbose=2 -p 4 \
       -- ./tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh
virtme: waiting for virtiofsd to start
...
[    3.546739] ip (260) used greatest stack depth: 12368 bytes left
[    3.609288] virtme-init: starting script
test_dynamic_debug_submod not there
test_dynamic_debug not there
# BASIC_TESTS 
...
# Done on: Fri Apr 26 20:45:08 MDT 2024
[    4.765751] virtme-init: script returned {0}
Powering off.
[    4.805790] ACPI: PM: Preparing to enter system sleep state S5
[    4.806223] kvm: exiting hardware virtualization
[    4.806564] reboot: Power down
[jimc@frodo vx]$ 


I've been running the kernel on my x86 desktop & laptop, booting with
drm.debug=0x1f, then turning it all-off after sleep 15.

a few highlights from a bare-metal boot:

here modprobe amdgpu; dyndbg applies last bit/class/category, and finishes init,
then drm and amdgpu start logging as they execute
...
[    9.019696] gandalf kernel: dyndbg: query 0: "class DRM_UT_ATOMIC +p" mod:amdgpu
[    9.019704] gandalf kernel: dyndbg: class-ref: amdgpu.DRM_UT_ATOMIC  module:amdgpu nd:4754 nc:0 nu:1
[    9.020012] gandalf kernel: dyndbg: processed 1 queries, with 21 matches, 0 errs
[    9.020017] gandalf kernel: dyndbg: bit_4: 21 matches on class: DRM_UT_ATOMIC -> 0x1f
[    9.020021] gandalf kernel: dyndbg: applied bitmap: 0x1f to: 0x0 for amdgpu
[    9.020026] gandalf kernel: dyndbg: attach-client-module:  module:amdgpu nd:4754 nc:0 nu:1
[    9.020031] gandalf kernel: dyndbg: 4754 debug prints in module amdgpu
[    9.055065] gandalf kernel: [drm] amdgpu kernel modesetting enabled.
[    9.055138] gandalf kernel: [drm:amdgpu_acpi_detect [amdgpu]] No matching acpi device found for AMD3000
[    9.055564] gandalf kernel: amdgpu: Virtual CRAT table created for CPU
[    9.055585] gandalf kernel: amdgpu: Topology: Add CPU node
[    9.055752] gandalf kernel: amdgpu 0000:0c:00.0: enabling device (0006 -> 0007)
[    9.055821] gandalf kernel: [drm] initializing kernel modesetting (NAVI10 0x1002:0x731F 0x148C:0x2398 0xC1).
[    9.055835] gandalf kernel: [drm] register mmio base: 0xFCB00000
[    9.055839] gandalf kernel: [drm] register mmio size: 524288
[    9.059148] gandalf kernel: [drm:amdgpu_discovery_set_ip_blocks [amdgpu]] number of dies: 1
[    9.059387] gandalf kernel: [drm:amdgpu_discovery_set_ip_blocks [amdgpu]] number of hardware IPs on die0: 39
[    9.059623] gandalf kernel: [drm:amdgpu_discovery_set_ip_blocks [amdgpu]] ATHUB(35) #0 v2.0.0:
[    9.059856] gandalf kernel: [drm:amdgpu_discovery_set_ip_blocks [amdgpu]]         0x00000c00
[    9.060096] gandalf kernel: [drm:amdgpu_discovery_set_ip_blocks [amdgpu]]         0x02408c00
[    9.060328] gandalf kernel: [drm:amdgpu_discovery_set_ip_blocks [amdgpu]] set register base offset for ATHUB

a startup script, after sleep 15, turns off the logging:

  echo 0 > /sys/module/drm/parameters/debug

heres 1st 2 bits/classes/categories being turned off:

[   29.105991] gandalf kernel: [drm:amdgpu_ih_process [amdgpu]] amdgpu_ih_process: rptr 90752, wptr 90784
[   29.118086] gandalf kernel: dyndbg: bits:0x0 > *.debug
[   29.118096] gandalf kernel: dyndbg: apply bitmap: 0x0 to: 0x1f for '*'
[   29.118102] gandalf kernel: dyndbg: query 0: "class DRM_UT_CORE -p" mod:*
[   29.118122] gandalf kernel: dyndbg: good-class: drm.DRM_UT_CORE  module:drm nd:338 nc:1 nu:0
[   29.119548] gandalf kernel: dyndbg: class-ref: drm_kms_helper.DRM_UT_CORE  module:drm_kms_helper nd:93 
nc:0 nu:1
[   29.119552] gandalf kernel: dyndbg: class-ref: drm_display_helper.DRM_UT_CORE  module:drm_display_helper nd:151 nc:0 nu:1
[   29.119737] gandalf kernel: dyndbg: class-ref: amdgpu.DRM_UT_CORE  module:amdgpu nd:4754 nc:0 nu:1
[   29.122181] gandalf kernel: [drm:amdgpu_ih_process [amdgpu]] amdgpu_ih_process: rptr 90784, wptr 90816
[   29.127687] gandalf kernel: dyndbg: processed 1 queries, with 466 matches, 0 errs
[   29.127690] gandalf kernel: dyndbg: bit_0: 466 matches on class: DRM_UT_CORE -> 0x0
[   29.127692] gandalf kernel: dyndbg: query 0: "class DRM_UT_DRIVER -p" mod:*
[   29.127696] gandalf kernel: dyndbg: good-class: drm.DRM_UT_DRIVER  module:drm nd:338 nc:1 nu:0
[   29.127699] gandalf kernel: dyndbg: class-ref: drm_kms_helper.DRM_UT_DRIVER  module:drm_kms_helper nd:93 nc:0 nu:1
[   29.127701] gandalf kernel: dyndbg: class-ref: drm_display_helper.DRM_UT_DRIVER  module:drm_display_helper nd:151 nc:0 nu:1
[   29.127885] gandalf kernel: dyndbg: class-ref: amdgpu.DRM_UT_DRIVER  module:amdgpu nd:4754 nc:0 nu:1
[   29.152925] gandalf kernel: dyndbg: processed 1 queries, with 1384 matches, 0 errs


The resulting journal is ~14.6k lines, written in the 1st 15 (29)
seconds of startup.  I'm unsure what the 15/29 discrepancy might
indicate/betray, besides a lot of logging work.  sleep 15 is not the
best stopwatch.

recent spins thru lkp-test have also been SUCCESS-ful.

Jim Cromie (35):

old-bugs & cleanups:
  dyndbg: fix old BUG_ON in >control parser
  docs/dyndbg: update examples \012 to \n
  test-dyndbg: fixup CLASSMAP usage error
  dyndbg: reword "class unknown," to "class:_UNKNOWN_"
  dyndbg: make ddebug_class_param union members same size
  dyndbg: replace classmap list with a vector
  dyndbg: ddebug_apply_class_bitmap - add module arg, select on it
  dyndbg: split param_set_dyndbg_classes to _module & wrapper fns
  dyndbg: drop NUM_TYPE_ARRAY
  dyndbg: reduce verbose/debug clutter
  dyndbg: silence debugs with no-change updates
  dyndbg: tighten ddebug_class_name() 1st arg type
  dyndbg: tighten fn-sig of ddebug_apply_class_bitmap
  dyndbg: reduce verbose=3 messages in ddebug_add_module
  dyndbg-API: remove DD_CLASS_TYPE_(DISJOINT|LEVEL)_NAMES and code

core fix & selftests:
  dyndbg-API: fix DECLARE_DYNDBG_CLASSMAP
  selftests-dyndbg: add tools/testing/selftests/dynamic_debug/*
  selftests-dyndbg: exit 127 if no facility
  dyndbg-API: promote DYNDBG_CLASSMAP_PARAM to API
  dyndbg-doc: add classmap info to howto
  dyndbg: treat comma as a token separator
  selftests-dyndbg: add comma_terminator_tests
  dyndbg: split multi-query strings with %
  selftests-dyndbg: test_percent_splitting multi-cmds on module classes
  docs/dyndbg: explain new delimiters: comma, percent
  selftests-dyndbg: add test_mod_submod
  selftests-dyndbg: test dyndbg-to-tracefs
  dyndbg-doc: explain flags parse 1st
  dyndbg: add __counted_by annotations

DRM parts
  drm+drivers: adapt to use DYNDBG_CLASSMAP_{DEFINE,USE}
  drm-dyndbg: adapt to use DYNDBG_CLASSMAP_PARAM
  drm: use correct ccflags-y spelling
  drm-drivers: DRM_CLASSMAP_USE in 2nd batch of drivers, helpers
  drm: restore CONFIG_DRM_USE_DYNAMIC_DEBUG un-BROKEN
  drm-print: workaround compiler meh

 .../admin-guide/dynamic-debug-howto.rst       |  99 ++-
 MAINTAINERS                                   |   3 +-
 drivers/gpu/drm/Kconfig                       |   3 +-
 drivers/gpu/drm/Makefile                      |   3 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c       |  12 +-
 drivers/gpu/drm/display/drm_dp_helper.c       |  12 +-
 drivers/gpu/drm/drm_crtc_helper.c             |  12 +-
 drivers/gpu/drm/drm_gem_shmem_helper.c        |   2 +
 drivers/gpu/drm/drm_print.c                   |  38 +-
 drivers/gpu/drm/gud/gud_drv.c                 |   2 +
 drivers/gpu/drm/i915/i915_params.c            |  12 +-
 drivers/gpu/drm/mgag200/mgag200_drv.c         |   2 +
 drivers/gpu/drm/nouveau/nouveau_drm.c         |  12 +-
 drivers/gpu/drm/qxl/qxl_drv.c                 |   2 +
 drivers/gpu/drm/radeon/radeon_drv.c           |   2 +
 drivers/gpu/drm/udl/udl_main.c                |   2 +
 drivers/gpu/drm/vkms/vkms_drv.c               |   2 +
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c           |   2 +
 include/asm-generic/vmlinux.lds.h             |   1 +
 include/drm/drm_print.h                       |  10 +
 include/linux/dynamic_debug.h                 | 130 ++-
 kernel/module/main.c                          |   3 +
 lib/Kconfig.debug                             |  24 +-
 lib/Makefile                                  |   3 +
 lib/dynamic_debug.c                           | 443 ++++++----
 lib/test_dynamic_debug.c                      | 131 +--
 lib/test_dynamic_debug_submod.c               |  17 +
 tools/testing/selftests/Makefile              |   1 +
 .../testing/selftests/dynamic_debug/Makefile  |   9 +
 tools/testing/selftests/dynamic_debug/config  |   2 +
 .../dynamic_debug/dyndbg_selftest.sh          | 765 ++++++++++++++++++
 31 files changed, 1398 insertions(+), 363 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

-- 
2.44.0