[PATCH v7 00/31] drm/dyndbg: Fix dynamic debug classmap regression

[PATCH v7 00/31] drm/dyndbg: Fix dynamic debug classmap regression

[Jim Cromie]

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

[PATCH v7 01/31] dyndbg: factor ddebug_match_desc out from ddebug_change

[Jim Cromie]

ddebug_change() is a big (~100 lines) function with a nested for loop.

The outer loop walks the per-module ddebug_tables list, and does
module stuff: it filters on a query's "module FOO*" and "class BAR",
failures here skip the entire inner loop.

The inner loop (60 lines) scans a module's descriptors.  It starts
with a long block of filters on function, line, format, and the
validated "BAR" class (or the legacy/_DPRINTK_CLASS_DFLT).

These filters "continue" past pr_debugs that don't match the query
criteria, before it falls through the code below that counts matches,
then adjusts the flags and static-keys.  This is unnecessarily hard to
think about.

So move the per-descriptor filter-block into a boolean function:
ddebug_match_desc(desc), and change each "continue" to "return false".
This puts a clear interface in place, so any future changes are either
inside, outside, or across this interface.

also fix checkpatch complaints about spaces and braces.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 lib/dynamic_debug.c | 83 +++++++++++++++++++++++++--------------------
 1 file changed, 47 insertions(+), 36 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 5a007952f7f2..eb5146bcfaca 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -171,6 +171,52 @@ static struct ddebug_class_map *ddebug_find_valid_class(struct ddebug_table cons
  * callsites, normally the same as number of changes.  If verbose,
  * logs the changes.  Takes ddebug_lock.
  */
+static bool ddebug_match_desc(const struct ddebug_query *query,
+			      struct _ddebug *dp,
+			      int valid_class)
+{
+	/* match site against query-class */
+	if (dp->class_id != valid_class)
+		return false;
+
+	/* match against the source filename */
+	if (query->filename &&
+	    !match_wildcard(query->filename, dp->filename) &&
+	    !match_wildcard(query->filename,
+			    kbasename(dp->filename)) &&
+	    !match_wildcard(query->filename,
+			    trim_prefix(dp->filename)))
+		return false;
+
+	/* match against the function */
+	if (query->function &&
+	    !match_wildcard(query->function, dp->function))
+		return false;
+
+	/* match against the format */
+	if (query->format) {
+		if (*query->format == '^') {
+			char *p;
+			/* anchored search. match must be at beginning */
+			p = strstr(dp->format, query->format + 1);
+			if (p != dp->format)
+				return false;
+		} else if (!strstr(dp->format, query->format)) {
+			return false;
+		}
+	}
+
+	/* match against the line number range */
+	if (query->first_lineno &&
+	    dp->lineno < query->first_lineno)
+		return false;
+	if (query->last_lineno &&
+	    dp->lineno > query->last_lineno)
+		return false;
+
+	return true;
+}
+
 static int ddebug_change(const struct ddebug_query *query,
 			 struct flag_settings *modifiers)
 {
@@ -203,42 +249,7 @@ static int ddebug_change(const struct ddebug_query *query,
 		for (i = 0; i < dt->num_ddebugs; i++) {
 			struct _ddebug *dp = &dt->ddebugs[i];
 
-			/* match site against query-class */
-			if (dp->class_id != valid_class)
-				continue;
-
-			/* match against the source filename */
-			if (query->filename &&
-			    !match_wildcard(query->filename, dp->filename) &&
-			    !match_wildcard(query->filename,
-					   kbasename(dp->filename)) &&
-			    !match_wildcard(query->filename,
-					   trim_prefix(dp->filename)))
-				continue;
-
-			/* match against the function */
-			if (query->function &&
-			    !match_wildcard(query->function, dp->function))
-				continue;
-
-			/* match against the format */
-			if (query->format) {
-				if (*query->format == '^') {
-					char *p;
-					/* anchored search. match must be at beginning */
-					p = strstr(dp->format, query->format+1);
-					if (p != dp->format)
-						continue;
-				} else if (!strstr(dp->format, query->format))
-					continue;
-			}
-
-			/* match against the line number range */
-			if (query->first_lineno &&
-			    dp->lineno < query->first_lineno)
-				continue;
-			if (query->last_lineno &&
-			    dp->lineno > query->last_lineno)
+			if (!ddebug_match_desc(query, dp, valid_class))
 				continue;
 
 			nfound++;
-- 
2.52.0