linux-kernel - [PATCH 06/18] dyndbg: fix a BUG_ON in ddebug_describe

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Date:   Thu,  5 Dec 2019 14:51:37 -0700
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org
Cc:     linux@...musvillemoes.dk, Jim Cromie <jim.cromie@...il.com>,
        kbuild test robot <lkp@...el.com>
Subject: [PATCH 06/18] dyndbg: fix a BUG_ON in ddebug_describe_flags

ddebug_describe_flags currently fills a caller provided string buffer,
after testing its size (also passed) in a BUG_ON.  Fix this with a
struct containing a known-big-enough string buffer, and passing it
instead.

Also simplify ddebug_describe_flags sig, and de-ref the struct in the
caller; this makes function reusable (soon) in contexts where flags
are already unpacked.

-v3 fix compile err introduced in patchset grooming.
Reported-by: kbuild test robot <lkp@...el.com>

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 lib/dynamic_debug.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index b5fb0aa0fbc3..49cb24948e12 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -62,6 +62,8 @@ struct ddebug_iter {
 	unsigned int idx;
 };
 
+struct flagsbuf { char buf[12]; };	/* big enough to hold all the flags */
+
 static DEFINE_MUTEX(ddebug_lock);
 static LIST_HEAD(ddebug_tables);
 static int verbose;
@@ -88,21 +90,19 @@ static struct { unsigned flag:8; char opt_char; } opt_array[] = {
 };
 
 /* format a string into buf[] which describes the _ddebug's flags */
-static char *ddebug_describe_flags(struct _ddebug *dp, char *buf,
-				    size_t maxlen)
+static char *ddebug_describe_flags(unsigned int flags, struct flagsbuf *fb)
 {
-	char *p = buf;
+	char *p = fb->buf;
 	int i;
 
-	BUG_ON(maxlen < 6);
 	for (i = 0; i < ARRAY_SIZE(opt_array); ++i)
-		if (dp->flags & opt_array[i].flag)
+		if (flags & opt_array[i].flag)
 			*p++ = opt_array[i].opt_char;
-	if (p == buf)
+	if (p == fb->buf)
 		*p++ = '_';
 	*p = '\0';
 
-	return buf;
+	return fb->buf;
 }
 
 #define vnpr_info(lvl, fmt, ...)				\
@@ -142,13 +142,13 @@ static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
  * logs the changes.  Takes ddebug_lock.
  */
 static int ddebug_change(const struct ddebug_query *query,
-			unsigned int flags, unsigned int mask)
+			unsigned int pflags, unsigned int mask)
 {
 	int i;
 	struct ddebug_table *dt;
 	unsigned int newflags;
 	unsigned int nfound = 0;
-	char flagbuf[10];
+	struct flagsbuf flags;
 
 	/* search for matching ddebugs */
 	mutex_lock(&ddebug_lock);
@@ -191,22 +191,21 @@ static int ddebug_change(const struct ddebug_query *query,
 
 			nfound++;
 
-			newflags = (dp->flags & mask) | flags;
+			newflags = (dp->flags & mask) | pflags;
 			if (newflags == dp->flags)
 				continue;
 #ifdef CONFIG_JUMP_LABEL
 			if (dp->flags & _DPRINTK_FLAGS_PRINT) {
-				if (!(flags & _DPRINTK_FLAGS_PRINT))
+				if (!(pflags & _DPRINTK_FLAGS_PRINT))
 					static_branch_disable(&dp->key.dd_key_true);
-			} else if (flags & _DPRINTK_FLAGS_PRINT)
+			} else if (pflags & _DPRINTK_FLAGS_PRINT)
 				static_branch_enable(&dp->key.dd_key_true);
 #endif
 			dp->flags = newflags;
 			vpr_info("changed %s:%d [%s]%s =%s\n",
 				 trim_prefix(dp->filename), dp->lineno,
 				 dt->mod_name, dp->function,
-				 ddebug_describe_flags(dp, flagbuf,
-						       sizeof(flagbuf)));
+				 ddebug_describe_flags(dp->flags, &flags));
 		}
 	}
 	mutex_unlock(&ddebug_lock);
@@ -820,7 +819,7 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
 {
 	struct ddebug_iter *iter = m->private;
 	struct _ddebug *dp = p;
-	char flagsbuf[10];
+	struct flagsbuf flags;
 
 	v9pr_info("called m=%p p=%p\n", m, p);
 
@@ -833,7 +832,7 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
 	seq_printf(m, "%s:%u [%s]%s =%s \"",
 		   trim_prefix(dp->filename), dp->lineno,
 		   iter->table->mod_name, dp->function,
-		   ddebug_describe_flags(dp, flagsbuf, sizeof(flagsbuf)));
+		   ddebug_describe_flags(dp->flags, &flags));
 	seq_escape(m, dp->format, "\t\r\n\"");
 	seq_puts(m, "\"\n");
 
-- 
2.23.0