Date: Mon, 27 May 2024 09:45:10 -0600
From: jim.cromie@...il.com
To: Łukasz Bartosik <ukaszb@...omium.org>
Cc: jbaron@...mai.com, gregkh@...uxfoundation.org, 
	linux-kernel@...r.kernel.org, linux@...musvillemoes.dk, joe@...ches.com, 
	mcgrof@...nel.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, 
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v8-RESEND 00/33] Fix CONFIG_DRM_USE_DYNAMIC_DEBUG=y regression

hi Łukasz

thanks for testing, and with all the config combos
that uncovered this problem.

On Sun, May 26, 2024 at 4:36 PM Łukasz Bartosik <ukaszb@...omium.org> wrote:
>
> On Thu, May 16, 2024 at 7:44 PM Jim Cromie <jim.cromie@...il.com> wrote:
> >
> > hi Greg, Jason,
> >
> > This patchset fixes the CONFIG_DRM_USE_DYNAMIC_DEBUG=y regression,
> > Fixes: bb2ff6c27bc9 ("drm: Disable dynamic debug as broken")
> >
> > Im calling it v8, to keep consistent with previous labels.
> > v6 was what got committed, back in 9/2022.
> > v7 had at least 2 problems that blocked its submission:
> >
> >  https://lore.kernel.org/lkml/20231101002609.3533731-1-jim.cromie@gmailcom/
> >  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 touched 2 subsystems at once, which would require
> > special handling.
> >
> > What was broken about DYNAMIC_DEBUG ?
> >
> > Booting a modular kernel with drm.debug=0x1ff enabled pr_debugs only
> > in drm itself, not in the yet-to-be loaded driver + helpers.  Once
> > loaded, the driver's pr_debugs are properly enabled by:
> >
> >    echo 0x1ff > /sys/module/drm/parameters/debug  # still worked
> >
> > I had tested with scripts doing lots of modprobes with various
> > permutations of dyndbg=<> option, and I missed that I didn't 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 (iirc shortly after committed), but the problem
> > hadn't been seen yet in CI.  One patchset across 2 subsystems didn't
> > help either.
> >
> > So 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 a driver's dependency on extern
> > __drm_debug).
> >
> > These 2 tell dyndbg to map "class FOO" to the defined FOO_ID, which
> > allows it to make those changes via >control, in both class definer
> > modules and dependent modules.
> >
> > 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 class'd pr_debugs 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, so
> > they can be applied later.  I've included them for anyone who wants to
> > test against DRM now.
> >
> > 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 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, and to guarantee that the submod always has the same
> > complement of debug()s, giving consistent output from both when
> > classmaps are working properly.
> >
> > Also ./tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh adds a
> > turn-key selftest.  I pulled it forward from a dyndbg-to-trace patchset
> > that I and Lukasz Bartozik have been working out.
> >
> > It works nicely from virtme-ng:
> >
> > [jimc@...do 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@...do 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.
> >
> > CC: Lukas Bartosik <ukaszb@...omium.org>
> > CC: Kees Cook <keescook@...omium.org>   # recent selftests/ reviews
> >
> > Jim Cromie (33):
> >
> > cleanups & preparations:
> >   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
> >
> > 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                 | 127 ++-
> >  kernel/module/main.c                          |   3 +
> >  lib/Kconfig.debug                             |  24 +-
> >  lib/Makefile                                  |   3 +
> >  lib/dynamic_debug.c                           | 435 ++++++----
> >  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, 1391 insertions(+), 359 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
> >
> > --
> > 2.45.0
> >
>
> Jim,
>
> With the TEST_DYNAMIC_DEBUG=M and TEST_DYNAMIC_DEBUG_SUBMOD=M self test passes
> .../selftests/dynamic_debug# ./dyndbg_selftest.sh
> # BASIC_TESTS
> # COMMA_TERMINATOR_TESTS
> # TEST_PERCENT_SPLITTING - multi-command splitting on %
> # TEST_MOD_SUBMOD
>
> However when (TEST_DYNAMIC_DEBUG=Y and TEST_DYNAMIC_DEBUG_SUBMOD=Y) or
>                          (TEST_DYNAMIC_DEBUG=Y and
> TEST_DYNAMIC_DEBUG_SUBMOD=M) self test fails with
>
> # TEST_PERCENT_SPLITTING - multi-command splitting on %
> test_dynamic_debug_submod not there
> test_dynamic_debug not there
> : ./dyndbg_selftest.sh:240 check failed expected 1 on =pf, got 0
>
> This happens because module is compiled into kernel and the following
> line does not modify classmaps
> modprobe test_dynamic_debug
> dyndbg=class,D2_CORE,+pf%class,D2_KMS,+pt%class,D2_ATOMIC,+pm
>
> Maybe selftest could verify if a module is compiled into a kernel and
> in such a case instead of calling modprobe as in the line above
> just do:
> ddcmd class,D2_CORE,+pf%class,D2_KMS,+pt%class,D2_ATOMIC,+pm
>
> What do you think ?
>

You found that problem by manual testing ?

[jimc@...do linux.git]$ cat tools/testing/selftests/dynamic_debug/config
CONFIG_TEST_DYNAMIC_DEBUG=m
CONFIG_TEST_DYNAMIC_DEBUG_SUBMOD=m

Im guessing that config file prevents the problem conf from getting tested in:
  make run_tests    # in selftests dir

so at least it shouldnt cause CI failures.
Is there any regular run-&-report of selftests I can subscribe to ?

on defconfig (iirc), I got:

[root@v6 linux.git]# ./tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh
: kernel not configured for this test

[ -e /proc/dynamic_debug/control ] || {
    echo -e "${RED}: kernel not configured for this test ${NC}"
    exit 127
}

1. We could add some more conditions to give up early.
2. Or we could avoid the mod-submod test if both modules arent modular.
(those are both easy-outs)

Also, builtin test modules are an unlikely choice generally.

Or, as you suggest, do something like
modprobe_or_apply_control( dyndbg_cmd_arg )
rmmod_or_undo_control ( undo_cmd_arg )

This is probably most thorough,
but it might be a game of whack-a-mole;
the test script exits at 1st failure,
there may be a bunch of them.

at least part of the problem is that rmmod really wipes all the
pr-debug settings,
which is a pretty strong precondition for the next test.

while not as robust as a full prdbg-state wipe,
the undo_arg could certainly undo the dyndbg_cmd_arg.
its a bit fiddly, but maybe just fiddle-once.

Im thinking that a combo of 1, 2 would suffice.
And we could probably drop the config constraints,
especially if the test avoids failing on configs where a failure is expected.
IOW - if no test-modules/builtins, run only 1st 3 tests, ending with PERCENT

That said, I wonder if the exit 127 should be success instead ?

thanks Lukas,
~jimc

> Thanks,
> Lukasz

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