diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index a7fae45..c37ec7c 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -13,6 +13,10 @@
 
 	If variable is of Type,		use printk format specifier:
 	------------------------------------------------------------
+		char			%hhd or %hhx
+		unsigned char		%hhu or %hhx
+		short int		%hd or %hx
+		unsigned short int	%hu or %hx
 		int			%d or %x
 		unsigned int		%u or %x
 		long			%ld or %lx
@@ -21,6 +25,10 @@
 		unsigned long long	%llu or %llx
 		size_t			%zu or %zx
 		ssize_t			%zd or %zx
+		s8			%hhd or %hhx
+		u8			%hhu or %hhx
+		s16			%hd or %hx
+		u16			%hu or %hx
 		s32			%d or %x
 		u32			%u or %x
 		s64			%lld or %llx
diff --git a/include/linux/kern_levels.h b/include/linux/kern_levels.h
index d237fe8..bf2389c 100644
--- a/include/linux/kern_levels.h
+++ b/include/linux/kern_levels.h
@@ -14,7 +14,7 @@
 #define KERN_INFO	KERN_SOH "6"	/* informational */
 #define KERN_DEBUG	KERN_SOH "7"	/* debug-level messages */
 
-#define KERN_DEFAULT	KERN_SOH "d"	/* the default kernel loglevel */
+#define KERN_DEFAULT	""		/* the default kernel loglevel */
 
 /*
  * Annotation for a "continued" line of log printout (only done after a
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 02b5c11..d7c77ed 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -18,7 +18,6 @@ static inline int printk_get_level(const char *buffer)
 	if (buffer[0] == KERN_SOH_ASCII && buffer[1]) {
 		switch (buffer[1]) {
 		case '0' ... '7':
-		case 'd':	/* KERN_DEFAULT */
 		case 'c':	/* KERN_CONT */
 			return buffer[1];
 		}
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index d3d1703..8eee85b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -344,7 +344,6 @@ static int console_msg_format = MSG_FORMAT_DEFAULT;
 
 enum log_flags {
 	LOG_NEWLINE	= 2,	/* text ended with a newline */
-	LOG_PREFIX	= 4,	/* text started with a prefix */
 	LOG_CONT	= 8,	/* text is a fragment of a continuation line */
 };
 
@@ -356,6 +355,9 @@ struct printk_log {
 	u8 facility;		/* syslog facility */
 	u8 flags:5;		/* internal record flags */
 	u8 level:3;		/* syslog level */
+#ifdef CONFIG_PRINTK_CALLER
+	u32 caller_id;            /* thread id or processor id */
+#endif
 }
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 __packed __aligned(4)
@@ -422,7 +424,11 @@ static u64 exclusive_console_stop_seq;
 static u64 clear_seq;
 static u32 clear_idx;
 
+#ifdef CONFIG_PRINTK_CALLER
+#define PREFIX_MAX		48
+#else
 #define PREFIX_MAX		32
+#endif
 #define LOG_LINE_MAX		(1024 - PREFIX_MAX)
 
 #define LOG_LEVEL(v)		((v) & 0x07)
@@ -577,7 +583,7 @@ static u32 truncate_msg(u16 *text_len, u16 *trunc_msg_len,
 }
 
 /* insert record into the buffer, discard old ones, update heads */
-static int log_store(int facility, int level,
+static int log_store(u32 caller_id, int facility, int level,
 		     enum log_flags flags, u64 ts_nsec,
 		     const char *dict, u16 dict_len,
 		     const char *text, u16 text_len)
@@ -625,6 +631,9 @@ static int log_store(int facility, int level,
 		msg->ts_nsec = ts_nsec;
 	else
 		msg->ts_nsec = local_clock();
+#ifdef CONFIG_PRINTK_CALLER
+	msg->caller_id = caller_id;
+#endif
 	memset(log_dict(msg) + dict_len, 0, pad_len);
 	msg->len = size;
 
@@ -688,12 +697,21 @@ static ssize_t msg_print_ext_header(char *buf, size_t size,
 				    struct printk_log *msg, u64 seq)
 {
 	u64 ts_usec = msg->ts_nsec;
+	char caller[20];
+#ifdef CONFIG_PRINTK_CALLER
+	u32 id = msg->caller_id;
+
+	snprintf(caller, sizeof(caller), ",caller=%c%u",
+		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
+#else
+	caller[0] = '\0';
+#endif
 
 	do_div(ts_usec, 1000);
 
-	return scnprintf(buf, size, "%u,%llu,%llu,%c;",
-		       (msg->facility << 3) | msg->level, seq, ts_usec,
-		       msg->flags & LOG_CONT ? 'c' : '-');
+	return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
+			 (msg->facility << 3) | msg->level, seq, ts_usec,
+			 msg->flags & LOG_CONT ? 'c' : '-', caller);
 }
 
 static ssize_t msg_print_ext_body(char *buf, size_t size,
@@ -1038,6 +1056,9 @@ void log_buf_vmcoreinfo_setup(void)
 	VMCOREINFO_OFFSET(printk_log, len);
 	VMCOREINFO_OFFSET(printk_log, text_len);
 	VMCOREINFO_OFFSET(printk_log, dict_len);
+#ifdef CONFIG_PRINTK_CALLER
+	VMCOREINFO_OFFSET(printk_log, caller_id);
+#endif
 }
 #endif
 
@@ -1236,10 +1257,23 @@ static size_t print_time(u64 ts, char *buf)
 {
 	unsigned long rem_nsec = do_div(ts, 1000000000);
 
-	return sprintf(buf, "[%5lu.%06lu] ",
+	return sprintf(buf, "[%5lu.%06lu]",
 		       (unsigned long)ts, rem_nsec / 1000);
 }
 
+#ifdef CONFIG_PRINTK_CALLER
+static size_t print_caller(u32 id, char *buf)
+{
+	char caller[12];
+
+	snprintf(caller, sizeof(caller), "%c%u",
+		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
+	return sprintf(buf, "[%6s]", caller);
+}
+#else
+#define print_caller(id, buf) 0
+#endif
+
 static size_t print_prefix(const struct printk_log *msg, bool syslog,
 			   bool time, char *buf)
 {
@@ -1247,8 +1281,17 @@ static size_t print_prefix(const struct printk_log *msg, bool syslog,
 
 	if (syslog)
 		len = print_syslog((msg->facility << 3) | msg->level, buf);
+
 	if (time)
 		len += print_time(msg->ts_nsec, buf + len);
+
+	len += print_caller(msg->caller_id, buf + len);
+
+	if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
+		buf[len++] = ' ';
+		buf[len] = '\0';
+	}
+
 	return len;
 }
 
@@ -1752,6 +1795,12 @@ static inline void printk_delay(void)
 	}
 }
 
+static inline u32 printk_caller_id(void)
+{
+	return in_task() ? task_pid_nr(current) :
+		0x80000000 + raw_smp_processor_id();
+}
+
 /*
  * Continuation lines are buffered, and not committed to the record buffer
  * until the line is complete, or a race forces it. The line fragments
@@ -1761,7 +1810,7 @@ static inline void printk_delay(void)
 static struct cont {
 	char buf[LOG_LINE_MAX];
 	size_t len;			/* length == 0 means unused buffer */
-	struct task_struct *owner;	/* task of first print*/
+	u32 caller_id;			/* printk_caller_id() of first print */
 	u64 ts_nsec;			/* time of first print */
 	u8 level;			/* log level of first message */
 	u8 facility;			/* log facility of first message */
@@ -1773,12 +1822,13 @@ static void cont_flush(void)
 	if (cont.len == 0)
 		return;
 
-	log_store(cont.facility, cont.level, cont.flags, cont.ts_nsec,
-		  NULL, 0, cont.buf, cont.len);
+	log_store(cont.caller_id, cont.facility, cont.level, cont.flags,
+		  cont.ts_nsec, NULL, 0, cont.buf, cont.len);
 	cont.len = 0;
 }
 
-static bool cont_add(int facility, int level, enum log_flags flags, const char *text, size_t len)
+static bool cont_add(u32 caller_id, int facility, int level,
+		     enum log_flags flags, const char *text, size_t len)
 {
 	/* If the line gets too long, split it up in separate records. */
 	if (cont.len + len > sizeof(cont.buf)) {
@@ -1789,7 +1839,7 @@ static bool cont_add(int facility, int level, enum log_flags flags, const char *
 	if (!cont.len) {
 		cont.facility = facility;
 		cont.level = level;
-		cont.owner = current;
+		cont.caller_id = caller_id;
 		cont.ts_nsec = local_clock();
 		cont.flags = flags;
 	}
@@ -1809,13 +1859,15 @@ static bool cont_add(int facility, int level, enum log_flags flags, const char *
 
 static size_t log_output(int facility, int level, enum log_flags lflags, const char *dict, size_t dictlen, char *text, size_t text_len)
 {
+	const u32 caller_id = printk_caller_id();
+
 	/*
 	 * If an earlier line was buffered, and we're a continuation
-	 * write from the same process, try to add it to the buffer.
+	 * write from the same context, try to add it to the buffer.
 	 */
 	if (cont.len) {
-		if (cont.owner == current && (lflags & LOG_CONT)) {
-			if (cont_add(facility, level, lflags, text, text_len))
+		if (cont.caller_id == caller_id && (lflags & LOG_CONT)) {
+			if (cont_add(caller_id, facility, level, lflags, text, text_len))
 				return text_len;
 		}
 		/* Otherwise, make sure it's flushed */
@@ -1828,12 +1880,13 @@ static size_t log_output(int facility, int level, enum log_flags lflags, const c
 
 	/* If it doesn't end in a newline, try to buffer the current line */
 	if (!(lflags & LOG_NEWLINE)) {
-		if (cont_add(facility, level, lflags, text, text_len))
+		if (cont_add(caller_id, facility, level, lflags, text, text_len))
 			return text_len;
 	}
 
 	/* Store it in the record log */
-	return log_store(facility, level, lflags, 0, dict, dictlen, text, text_len);
+	return log_store(caller_id, facility, level, lflags, 0,
+			 dict, dictlen, text, text_len);
 }
 
 /* Must be called under logbuf_lock. */
@@ -1867,9 +1920,6 @@ int vprintk_store(int facility, int level,
 			case '0' ... '7':
 				if (level == LOGLEVEL_DEFAULT)
 					level = kern_level - '0';
-				/* fallthrough */
-			case 'd':	/* KERN_DEFAULT */
-				lflags |= LOG_PREFIX;
 				break;
 			case 'c':	/* KERN_CONT */
 				lflags |= LOG_CONT;
@@ -1884,7 +1934,7 @@ int vprintk_store(int facility, int level,
 		level = default_message_loglevel;
 
 	if (dict)
-		lflags |= LOG_PREFIX|LOG_NEWLINE;
+		lflags |= LOG_NEWLINE;
 
 	return log_output(facility, level, lflags,
 			  dict, dictlen, text, text_len);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e718487..91ed812 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -17,6 +17,23 @@
 	  The behavior is also controlled by the kernel command line
 	  parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst
 
+config PRINTK_CALLER
+	bool "Show caller information on printks"
+	depends on PRINTK
+	help
+	  Selecting this option causes printk() to add a caller "thread id" (if
+	  in task context) or a caller "processor id" (if not in task context)
+	  to every message.
+
+	  This option is intended for environments where multiple threads
+	  concurrently call printk() for many times, for it is difficult to
+	  interpret without knowing where these lines (or sometimes individual
+	  line which was divided into multiple lines due to race) came from.
+
+	  Since toggling after boot makes the code racy, currently there is
+	  no option to enable/disable at the kernel command line parameter or
+	  sysfs interface.
+
 config CONSOLE_LOGLEVEL_DEFAULT
 	int "Default console loglevel (1-15)"
 	range 1 15
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 30b00de..791b6fa 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1931,7 +1931,6 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
  *       (legacy clock framework) of the clock
  * - 'Cn' For a clock, it prints the name (Common Clock Framework) or address
  *        (legacy clock framework) of the clock
- * - 'Cr' For a clock, it prints the current rate of the clock
  * - 'G' For flags to be printed as a collection of symbolic strings that would
  *       construct the specific value. Supported flags given by option:
  *       p page flags (see struct page) given as pointer to unsigned long