linux-kernel - [PATCH 21/30] dyndbg: detect class

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Message-ID: <20250911213823.374806-22-jim.cromie@gmail.com>
Date: Thu, 11 Sep 2025 15:38:14 -0600
From: Jim Cromie <jim.cromie@...il.com>
To: jbaron@...mai.com
Cc: gregkh@...uxfoundation.org,
	ukaszb@...omium.org,
	louis.chauvet@...tlin.com,
	linux-kernel@...r.kernel.org,
	Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH 21/30] dyndbg: detect class_id reservation conflicts

If a module _DEFINEs 2 or more classmaps, it must devise them to share
the per-module 0..62 class-id space; ie their respective base,+length
reservations cannot overlap.

To detect conflicts at modprobe, add ddebug_class_range_overlap(),
call it from ddebug_add_module(), and WARN and return -EINVAL when
they're detected.

This insures that class_id -> classname lookup has just 1 answer, so
the 1st-found search in find-class-name works properly.

test_dynamic_debug.c:

If built with -DFORCE_CLASSID_CONFLICT, the test-modules invoke 2
conflicting DYNAMIC_DEBUG_CLASSMAP_DEFINE() declarations, into parent
and the _submod.  These conflict with one of the good ones in the
parent (D2_CORE..etc), causing the modprobe(s) to warn

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
- USE doesnt need conflict test against DEFINE
  infact its wrong-headed - of course theyd overlap.
---
 lib/dynamic_debug.c      | 27 +++++++++++++++++++++++++++
 lib/test_dynamic_debug.c |  8 ++++++++
 2 files changed, 35 insertions(+)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 54f93d1d0ff2..b6a5219d71af 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -1267,6 +1267,22 @@ static void ddebug_apply_class_users(const struct _ddebug_info *di)
 	(_dst)->info._vec.len = nc;					\
 })
 
+static int __maybe_unused
+ddebug_class_range_overlap(struct _ddebug_class_map *cm,
+			   u64 *reserved_ids)
+{
+	u64 range = (((1ULL << cm->length) - 1) << cm->base);
+
+	if (range & *reserved_ids) {
+		pr_err("[%d..%d] on %s conflicts with %llx\n", cm->base,
+		       cm->base + cm->length - 1, cm->class_names[0],
+		       *reserved_ids);
+		return -EINVAL;
+	}
+	*reserved_ids |= range;
+	return 0;
+}
+
 /*
  * Allocate a new ddebug_table for the given module
  * and add it to the global list.
@@ -1276,6 +1292,7 @@ static int ddebug_add_module(struct _ddebug_info *di)
 	struct ddebug_table *dt;
 	struct _ddebug_class_map *cm;
 	struct _ddebug_class_user *cli;
+	u64 reserved_ids = 0;
 	int i;
 
 	if (!di->descs.len)
@@ -1300,6 +1317,11 @@ static int ddebug_add_module(struct _ddebug_info *di)
 	dd_mark_vector_subrange(i, dt, cli, di, users);
 	/* now di may be stale */
 
+	/* insure 2+ classmaps share the per-module 0..62 class_id space */
+	for_subvec(i, cm, di, maps)
+		if (ddebug_class_range_overlap(cm, &reserved_ids))
+			goto cleanup;
+
 	mutex_lock(&ddebug_lock);
 	list_add_tail(&dt->link, &ddebug_tables);
 	mutex_unlock(&ddebug_lock);
@@ -1312,6 +1334,11 @@ static int ddebug_add_module(struct _ddebug_info *di)
 	vpr_info("%3u debug prints in module %s\n",
 		 dt->info.descs.len, dt->info.mod_name);
 	return 0;
+cleanup:
+	WARN_ONCE("dyndbg multi-classmap conflict in %s\n", di->mod_name);
+	kfree(dt);
+	return -EINVAL;
+
 }
 
 /* helper for ddebug_dyndbg_(boot|module)_param_cb */
diff --git a/lib/test_dynamic_debug.c b/lib/test_dynamic_debug.c
index 6c4548f63512..1ba4be9a403a 100644
--- a/lib/test_dynamic_debug.c
+++ b/lib/test_dynamic_debug.c
@@ -128,6 +128,14 @@ DYNAMIC_DEBUG_CLASSMAP_DEFINE(map_level_num, DD_CLASS_TYPE_LEVEL_NUM,
 DYNAMIC_DEBUG_CLASSMAP_PARAM(disjoint_bits, p);
 DYNAMIC_DEBUG_CLASSMAP_PARAM(level_num, p);
 
+#ifdef FORCE_CLASSID_CONFLICT
+/*
+ * Enable with -Dflag on compile to test overlapping class-id range
+ * detection.  This should warn on modprobes.
+ */
+DYNDBG_CLASSMAP_DEFINE(classid_range_conflict, 0, D2_CORE + 1, "D3_CORE");
+#endif
+
 #else /* TEST_DYNAMIC_DEBUG_SUBMOD */
 
 /*
-- 
2.51.0