linux-kernel - [RFC PATCH v5 28/28] dyndbg: RFC drop

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Date:   Tue, 11 May 2021 12:50:57 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     Jason Baron <jbaron@...mai.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, Jim Cromie <jim.cromie@...il.com>
Subject: [RFC PATCH v5 28/28] dyndbg: RFC drop _ddebug.site pointer

In .h, flip the switch on #define SITE_CHK.  This finally removes the
_ddebug.site pointer, and all uses of it.  Due to this, the .site
cross-link done by DEFINE_DYNAMIC_DEBUG_METADATA() is lost to the
compiler, so suppress the resulting warnings by adding a "__used" to
the _ddebug_site records initialized there.

In .c, fix a bunch of fallout:
- mostly casts from struct to/from union
- convert a BUG_ON to a WARN,
  it happens ~20x per `cat control`, probably headers on loaded modules
- fixup missing _ddebug_header.site,
  bad initialization of some sort.

This seems to work, but should be cleaner.  RFC

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/linux/dynamic_debug.h |  4 ++--
 lib/dynamic_debug.c           | 25 +++++++++++++++++--------
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 9ca413985fb2..7f2b255a25ae 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -6,7 +6,7 @@
 #include <linux/jump_label.h>
 #endif
 
-#define SITE_CHK /* include .site pointer and checks on it */
+// #define SITE_CHK /* include .site pointer and checks on it */
 
 #ifdef SITE_CHK
 #define SITE_CHK_(...)		__VA_ARGS__
@@ -135,7 +135,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 			 const char *fmt, ...);
 
 #define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt)		\
-	static struct _ddebug_site  __aligned(8)		\
+	static struct _ddebug_site  __aligned(8) __used		\
 	__section("__dyndbg_sites") name##_site = {		\
 		.modname = KBUILD_MODNAME,			\
 		.filename = __FILE__,				\
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index aa4a476d70ad..db759c998c54 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -148,9 +148,12 @@ static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
 
 static struct _ddebug_site *ddebug_site_get(struct _ddebug *dp)
 {
-	struct _ddebug *dh = dp - (dp->_index);
+	union _ddebug_header *dh = (union _ddebug_header *) (dp - dp->_index);
+
+	if (!is_dyndbg_header_pair(dh, dh->site)) {
+		v3pr_info("get: header fail\n");
+	}
 
-	BUG_ON(!is_dyndbg_header_pair(dh, dh->site));
 #ifdef SITE_CHK
 	if (dp >= __start___dyndbg && dp < __stop___dyndbg) {
 
@@ -178,7 +181,7 @@ static struct _ddebug_site *ddebug_site_get(struct _ddebug *dp)
 
 	return dp->site;
 #else
-	return &dh->site[dp->_index];
+	return (struct _ddebug_site *) &dh->site[dp->_index];
 #endif
 }
 static inline void ddebug_site_put(struct _ddebug *dp)
@@ -1070,17 +1073,23 @@ static int __ddebug_add_module(struct _ddebug *tab, struct _ddebug_site *sites,
 			       const char *modname)
 {
 	struct ddebug_table *dt;
+	union _ddebug_header *dh = (union _ddebug_header *) &tab[0];
 	int i;
 
 	v3pr_info("add-module: %s.%d sites\n", modname, numdbgs);
 
-	if (numdbgs && is_dyndbg_header_pair(tab, sites)) {
+	if (numdbgs && is_dyndbg_header_pair(dh, sites)) {
 
-		v3pr_info(" header: %d %s.%s.%d\n", tab[0]._index, modname,
-			  tab[0].site->function, tab[0].lineno);
+		v3pr_info(" header: %d %s.\n", dh->_index, modname);
 
-		SITE_CHK_(BUG_ON(tab[0].site != &sites[0]));
+		SITE_CHK_(BUG_ON(dh->site[0] != &sites[0]));
 
+		/* for !SITE_CHK, need to set site ptr, fixup missed init! */
+		if (!dh->site) {
+			dh->site = (union _ddebug_site_header *) sites;
+			v3pr_info(" header: %d %s.%s.%d\n", dh->_index, modname,
+				  dh->site->function, dh->lineno);
+		}
 		if (numdbgs <= 1) {
 			v3pr_info(" skip header %s\n", modname);
 			return 0;
@@ -1110,7 +1119,7 @@ static int __ddebug_add_module(struct _ddebug *tab, struct _ddebug_site *sites,
 	for (i = 0; i < numdbgs; i++, base++) {
 		tab[i]._index = base;
 		v3pr_info(" %d %d %s.%s.%d\n", i, base, modname,
-			  tab[i].site->function, tab[i].lineno);
+			  sites[i].function, tab[i].lineno);
 	}
 
 	mutex_lock(&ddebug_lock);
-- 
2.31.1