linux-kernel - [RFC PATCH 00/17] DRM_USE_DYNAMIC

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Message-Id: <20221206003424.592078-1-jim.cromie@gmail.com>
Date:   Mon,  5 Dec 2022 17:34:07 -0700
From:   Jim Cromie <jim.cromie@...il.com>
To:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org, intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org
Cc:     jani.nikula@...el.com, ville.syrjala@...ux.intel.com,
        daniel.vetter@...ll.ch, seanpaul@...omium.org, robdclark@...il.com,
        jbaron@...mai.com, gregkh@...uxfoundation.org,
        Jim Cromie <jim.cromie@...il.com>
Subject: [RFC PATCH 00/17] DRM_USE_DYNAMIC_DEBUG regression

Hi everyone,

DRM_USE_DYNAMIC_DEBUG=y has a regression on rc-*

Regression is due to a chicken-egg problem loading modules; on
`modprobe i915`, drm is loaded 1st, and drm.debug is set.  When
drm_debug_enabled() tested __drm_debug at runtime, that just worked.

But with DRM_USE_DYNAMIC_DEBUG=y, the runtime test is replaced with a
post-load enablement of drm_dbg/dyndbg callsites (static-keys), via
dyndbg's callback on __drm_debug.  Since all drm-drivers need drm.ko,
it is loaded 1st, then drm.debug=X is applied, then drivers load, but
too late for drm_dbgs to be enabled.

STATUS

For all-loadable drm,i915,amdgpu configs, it almost works, but
propagating drm.debug to dependent modules doesnt actually apply,
though the motions are there.  This is not the problem I want to chase
here.

The more basic trouble is:

For builtin drm + helpers, things are broken pretty early; at the
beginning of dynamic_debug_init().  As the ddebug_sanity() commit-msg
describes in some detail, the records added by _USE fail to reference
the struct ddebug_class_map created and exported by _DEFINE, but get
separate addresses to "other" data that segv's when used as the
expected pointer. FWIW, the pointer val starts with "revi".

OVERVIEW

DECLARE_DYNDBG_CLASSMAP is broken: it is one-size-fits-all-poorly.
It muddles the distinction between a (single) definition, and multiple
references.  Something exported should suffice.

The core of this patchset splits it into:

DYNDBG_CLASSMAP_DEFINE	used once per subsystem to define each classmap
DYNDBG_CLASSMAP_USE	declare dependence on a DEFINEd classmap

This makes the weird coordinated-changes-by-identical-classmaps
"feature" unnecessary; the DEFINE can export the var, and USE refers
to the exported var.

So this patchset adds another section: __dyndbg_class_refs.

It is like __dyndbg_classes; it is scanned under ddebug_add_module(),
and attached to each module's ddebug_table.  Once attached, it can be
used like classes to validate and apply class FOO >control queries.

It also maps the class user -> definer explicitly, so that when the
module is loaded, the section scan can find the kernel-param that is
wired to dyndbg's kparam-callback, and apply its state-var, forex:
__drm_debug to the just loaded helper/driver module.

Theres plenty to address Im sure.

Jim Cromie (17):
  test-dyndbg: fixup CLASSMAP usage error
  test-dyndbg: show that DEBUG enables prdbgs at compiletime
  dyndbg: fix readback value on LEVEL_NAMES interfaces
  dyndbg: replace classmap list with a vector
  dyndbg: make ddebug_apply_class_bitmap more selective
  dyndbg: dynamic_debug_init - use pointer inequality, not strcmp
  dyndbg: drop NUM_TYPE_ARRAY
  dyndbg: reduce verbose/debug clutter
  dyndbg-API: replace DECLARE_DYNDBG_CLASSMAP with
    DYNDBG_CLASSMAP(_DEFINE|_USE)
  dyndbg-API: specialize DYNDBG_CLASSMAP_(DEFINE|USE)
  dyndbg-API: DYNDBG_CLASSMAP_USE drop extra args
  dyndbg-API: DYNDBG_CLASSMAP_DEFINE() improvements
  drm_print: fix stale macro-name in comment
  dyndbg: unwrap __ddebug_add_module inner function NOTYET
  dyndbg: ddebug_sanity()
  dyndbg: mess-w-dep-class
  dyndbg: miss-on HACK

 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c |  14 +-
 drivers/gpu/drm/display/drm_dp_helper.c |  14 +-
 drivers/gpu/drm/drm_crtc_helper.c       |  14 +-
 drivers/gpu/drm/drm_print.c             |  22 +--
 drivers/gpu/drm/i915/i915_params.c      |  14 +-
 drivers/gpu/drm/nouveau/nouveau_drm.c   |  14 +-
 include/asm-generic/vmlinux.lds.h       |   3 +
 include/drm/drm_print.h                 |   6 +-
 include/linux/dynamic_debug.h           |  57 ++++--
 include/linux/map.h                     |  54 ++++++
 kernel/module/main.c                    |   2 +
 lib/dynamic_debug.c                     | 240 +++++++++++++++++++-----
 lib/test_dynamic_debug.c                |  47 ++---
 13 files changed, 344 insertions(+), 157 deletions(-)
 create mode 100644 include/linux/map.h

-- 
2.38.1