linux-kernel - [RFC PATCH v5 24/28] dyndbg: make site pointer and checks on it optional (not quite)

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Date:   Tue, 11 May 2021 12:50:53 -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 24/28] dyndbg: make site pointer and checks on it optional (not quite)

Wrap declaration and uses of _ddebug.site pointer in ifdefs.
Mostly, this eliminates all the WARN_ONs in ddebug_site_get(),
which seem to be mostly proven (they were BUG_ONs).

This adds macro indirection around ifdef SITE_CHK; adding SITE_INIT_
to adjust the .site initializations, and SITE_COND, which abstracts a
logic test used by is_dyndbg_header_pair(i,s).

TODO: breaks when !defined SITE_CHK - the header, being just a struct
_ddebug, also lost the .site member.  Need to specialize the header
struct, then unionize it back in.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/linux/dynamic_debug.h | 20 ++++++++++++++++----
 lib/dynamic_debug.c           | 13 ++++++++++---
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 06ae1d8d8c10..46901b5348ee 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -6,6 +6,18 @@
 #include <linux/jump_label.h>
 #endif
 
+#define SITE_CHK /* include .site pointer and checks on it */
+
+#ifdef SITE_CHK
+#define SITE_CHK_(...)		__VA_ARGS__
+#define SITE_COND(_i, _s)	(_s == _i->site)
+#define SITE_INIT_(_name)	.site = &_name,
+#else
+#define SITE_CHK_(...)
+#define SITE_COND(_i, _s)	(true)
+#define SITE_INIT_(name)
+#endif
+
 /*
  * A pair of these structs are created in 2 special ELF sections
  * (__dyndbg, __dyndbg_sites) for every dynamic debug callsite.
@@ -25,7 +37,7 @@ struct _ddebug_site {
 } __aligned(8);
 
 struct _ddebug {
-	struct _ddebug_site *site;
+	SITE_CHK_(struct _ddebug_site *site;)
 	/* format is always needed, lineno shares word with flags */
 	const char *format;
 	const unsigned lineno:18;
@@ -106,7 +118,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 	};							\
 	static struct _ddebug  __aligned(8)			\
 	__section("__dyndbg") name = {				\
-		.site = &name##_site,				\
+		SITE_INIT_(name##_site)				\
 		.format = (fmt),				\
 		.lineno = __LINE__,				\
 		.flags = _DPRINTK_FLAGS_DEFAULT,		\
@@ -138,13 +150,13 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 	__weak struct _ddebug __used __aligned(8)		\
 		__section(".gnu.linkonce.dyndbg")		\
 	_LINKONCE_dyndbg_header = {				\
-		.site = &_LINKONCE_dyndbg_site_header,		\
+		SITE_INIT_(_LINKONCE_dyndbg_site_header)	\
 		.format = KBUILD_MODNAME			\
 	}
 
 /* The header initializations as a distinguishing predicate */
 #define is_dyndbg_header_pair(iter, sitep)			\
-	(sitep == iter->site					\
+	(SITE_COND(iter, sitep)					\
 	 && (!iter->lineno)					\
 	 && (iter->format == sitep->modname)			\
 	 && (sitep->modname == sitep->function)			\
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index b83187e72ee0..9551c0d406b6 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -151,7 +151,7 @@ static struct _ddebug_site *ddebug_site_get(struct _ddebug *dp)
 	struct _ddebug *dh = dp - (dp->_index);
 
 	WARN_ON(!is_dyndbg_header_pair(dh, dh->site));
-
+#ifdef SITE_CHK
 	if (dp >= __start___dyndbg && dp < __stop___dyndbg) {
 
 		v5pr_info("get: %s is builtin: %d %s:%s:%d\n",
@@ -177,6 +177,9 @@ static struct _ddebug_site *ddebug_site_get(struct _ddebug *dp)
 		WARN_ON(&dh->site[dp->_index] != dp->site);
 
 	return dp->site;
+#else
+	return &dh->site[dp->_index];
+#endif
 }
 static inline void ddebug_site_put(struct _ddebug *dp)
 {
@@ -241,6 +244,7 @@ static void ddebug_alter_site(struct _ddebug *dp,
 	} else if (modifiers->flags & _DPRINTK_FLAGS_PRINT)
 		static_branch_enable(&dp->key.dd_key_true);
 #endif
+#ifdef SITE_CHK
 	/* delete site info for this callsite */
 	if (modifiers->flags & _DPRINTK_FLAGS_DELETE_SITE) {
 		if (dp->site) {
@@ -249,6 +253,7 @@ static void ddebug_alter_site(struct _ddebug *dp,
 			dp->site = NULL;
 		}
 	}
+#endif
 }
 
 /*
@@ -1073,7 +1078,9 @@ static int __ddebug_add_module(struct _ddebug *tab, struct _ddebug_site *sites,
 
 		v3pr_info(" header: %d %s.%s.%d\n", tab[0]._index, modname,
 			  tab[0].site->function, tab[0].lineno);
-		WARN_ON(tab[0].site != &sites[0]);
+
+		SITE_CHK_(BUG_ON(tab[0].site != &sites[0]));
+
 		if (numdbgs <= 1) {
 			v3pr_info(" skip header %s\n", modname);
 			return 0;
@@ -1251,7 +1258,7 @@ static int __init dynamic_debug_init(void)
 
 	for (i = 0; iter < __stop___dyndbg; iter++, site++, i++) {
 
-		WARN_ON(site != iter->site);
+		SITE_CHK_(WARN_ON(site != iter->site));
 
 		if (strcmp(modname, site->modname)) {
 			modct++;
-- 
2.31.1