[RFC 4/4] kernel/panic: add verbose logging of kernel taints in backtraces

[Jani Nikula]

With nearly 20 taint flags and respective characters, it's getting a bit
difficult to remember what each taint flag character means. Add verbose
logging of the set taints in the format:

Tainted: [P]=PROPRIETARY_MODULE, [W]=WARN

in dump_stack_print_info() when there are taints.

Note that the "negative flag" G is not included.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
---
 include/linux/panic.h |  8 +++++---
 kernel/panic.c        | 45 ++++++++++++++++++++++++++++++++-----------
 lib/dump_stack.c      |  3 +++
 3 files changed, 42 insertions(+), 14 deletions(-)

diff --git a/include/linux/panic.h b/include/linux/panic.h
index 6717b15e798c..3130e0b5116b 100644
--- a/include/linux/panic.h
+++ b/include/linux/panic.h
@@ -77,9 +77,10 @@ static inline void set_arch_panic_timeout(int timeout, int arch_default_timeout)
 #define TAINT_FLAGS_MAX			((1UL << TAINT_FLAGS_COUNT) - 1)
 
 struct taint_flag {
-	char c_true;	/* character printed when tainted */
-	char c_false;	/* character printed when not tainted */
-	bool module;	/* also show as a per-module taint flag */
+	char c_true;		/* character printed when tainted */
+	char c_false;		/* character printed when not tainted */
+	bool module;		/* also show as a per-module taint flag */
+	const char *desc;	/* verbose description of the set taint flag */
 };
 
 extern const struct taint_flag taint_flags[TAINT_FLAGS_COUNT];
@@ -90,6 +91,7 @@ enum lockdep_ok {
 };
 
 extern const char *print_tainted(void);
+extern const char *print_tainted_verbose(void);
 extern void add_taint(unsigned flag, enum lockdep_ok);
 extern int test_taint(unsigned flag);
 extern unsigned long get_taint(void);
diff --git a/kernel/panic.c b/kernel/panic.c
index e1f87ba51ba1..ed270d3b5f2b 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -477,6 +477,7 @@ EXPORT_SYMBOL(panic);
 	[ TAINT_##taint ] = {						\
 		.c_true = _c_true, .c_false = _c_false,			\
 		.module = _module,					\
+		.desc = #taint,						\
 	}
 
 /*
@@ -507,8 +508,9 @@ const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
 
 #undef TAINT_FLAG
 
-static void print_tainted_seq(struct seq_buf *s)
+static void print_tainted_seq(struct seq_buf *s, bool verbose)
 {
+	const char *sep = "";
 	int i;
 
 	if (!tainted_mask) {
@@ -522,10 +524,32 @@ static void print_tainted_seq(struct seq_buf *s)
 		bool is_set = test_bit(i, &tainted_mask);
 		char c = is_set ? t->c_true : t->c_false;
 
-		seq_buf_putc(s, c);
+		if (verbose) {
+			if (is_set) {
+				seq_buf_printf(s, "%s[%c]=%s", sep, c, t->desc);
+				sep = ", ";
+			}
+		} else {
+			seq_buf_putc(s, c);
+		}
 	}
 }
 
+static const char *_print_tainted(bool verbose)
+{
+	/* FIXME: what should the size be? */
+	static char buf[sizeof(taint_flags)];
+	struct seq_buf s;
+
+	BUILD_BUG_ON(ARRAY_SIZE(taint_flags) != TAINT_FLAGS_COUNT);
+
+	seq_buf_init(&s, buf, sizeof(buf));
+
+	print_tainted_seq(&s, verbose);
+
+	return seq_buf_str(&s);
+}
+
 /**
  * print_tainted - return a string to represent the kernel taint state.
  *
@@ -536,16 +560,15 @@ static void print_tainted_seq(struct seq_buf *s)
  */
 const char *print_tainted(void)
 {
-	static char buf[TAINT_FLAGS_COUNT + sizeof("Tainted: ")];
-	struct seq_buf s;
-
-	BUILD_BUG_ON(ARRAY_SIZE(taint_flags) != TAINT_FLAGS_COUNT);
-
-	seq_buf_init(&s, buf, sizeof(buf));
-
-	print_tainted_seq(&s);
+	return _print_tainted(false);
+}
 
-	return seq_buf_str(&s);
+/**
+ * print_tainted_verbose - A more verbose version of print_tainted()
+ */
+const char *print_tainted_verbose(void)
+{
+	return _print_tainted(true);
 }
 
 int test_taint(unsigned flag)
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 222c6d6c8281..8b6b70eaf949 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -62,6 +62,9 @@ void dump_stack_print_info(const char *log_lvl)
 	       (int)strcspn(init_utsname()->version, " "),
 	       init_utsname()->version, BUILD_ID_VAL);
 
+	if (get_taint())
+		printk("%s%s\n", log_lvl, print_tainted_verbose());
+
 	if (dump_stack_arch_desc_str[0] != '\0')
 		printk("%sHardware name: %s\n",
 		       log_lvl, dump_stack_arch_desc_str);
-- 
2.39.2