Merge tag 'printk-for-4.21' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk

Pull printk updates from Petr Mladek:

 - Keep spinlocks busted until the end of panic()

 - Fix races between calculating number of messages that would fit into
   user space buffers, filling the buffers, and switching printk.time
   parameter

 - Some code clean up

* tag 'printk-for-4.21' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk:
  printk: Remove print_prefix() calls with NULL buffer.
  printk: fix printk_time race.
  printk: Make printk_emit() local function.
  panic: avoid deadlocks in re-entrant console drivers

include/linux/printk.h

@@ -166,11 +166,6 @@ int vprintk_emit(int facility, int level,
 asmlinkage __printf(1, 0)
 int vprintk(const char *fmt, va_list args);
 
-asmlinkage __printf(5, 6) __cold
-int printk_emit(int facility, int level,
-		const char *dict, size_t dictlen,
-		const char *fmt, ...);
-
 asmlinkage __printf(1, 2) __cold
 int printk(const char *fmt, ...);
 

kernel/panic.c

@@ -14,6 +14,7 @@
 #include <linux/kmsg_dump.h>
 #include <linux/kallsyms.h>
 #include <linux/notifier.h>
+#include <linux/vt_kern.h>
 #include <linux/module.h>
 #include <linux/random.h>
 #include <linux/ftrace.h>
@@ -237,7 +238,10 @@ void panic(const char *fmt, ...)
 	if (_crash_kexec_post_notifiers)
 		__crash_kexec(NULL);
 
-	bust_spinlocks(0);
+#ifdef CONFIG_VT
+	unblank_screen();
+#endif
+	console_unblank();
 
 	/*
 	 * We may have ended up stopping the CPU holding the lock (in

kernel/printk/printk.c

@@ -403,6 +403,7 @@ DECLARE_WAIT_QUEUE_HEAD(log_wait);
 static u64 syslog_seq;
 static u32 syslog_idx;
 static size_t syslog_partial;
+static bool syslog_time;
 
 /* index and sequence number of the first record stored in the buffer */
 static u64 log_first_seq;
@@ -752,6 +753,19 @@ struct devkmsg_user {
 	char buf[CONSOLE_EXT_LOG_MAX];
 };
 
+static __printf(3, 4) __cold
+int devkmsg_emit(int facility, int level, const char *fmt, ...)
+{
+	va_list args;
+	int r;
+
+	va_start(args, fmt);
+	r = vprintk_emit(facility, level, NULL, 0, fmt, args);
+	va_end(args);
+
+	return r;
+}
+
 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
 {
 	char *buf, *line;
@@ -810,7 +824,7 @@ static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
 		}
 	}
 
-	printk_emit(facility, level, NULL, 0, "%s", line);
+	devkmsg_emit(facility, level, "%s", line);
 	kfree(buf);
 	return ret;
 }
@@ -1213,50 +1227,39 @@ static inline void boot_delay_msec(int level)
 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 
-static size_t print_time(u64 ts, char *buf)
+static size_t print_syslog(unsigned int level, char *buf)
 {
-	unsigned long rem_nsec;
-
-	if (!printk_time)
-		return 0;
-
-	rem_nsec = do_div(ts, 1000000000);
+	return sprintf(buf, "<%u>", level);
+}
 
-	if (!buf)
-		return snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)ts);
+static size_t print_time(u64 ts, char *buf)
+{
+	unsigned long rem_nsec = do_div(ts, 1000000000);
 
 	return sprintf(buf, "[%5lu.%06lu] ",
 		       (unsigned long)ts, rem_nsec / 1000);
 }
 
-static size_t print_prefix(const struct printk_log *msg, bool syslog, char *buf)
+static size_t print_prefix(const struct printk_log *msg, bool syslog,
+			   bool time, char *buf)
 {
 	size_t len = 0;
-	unsigned int prefix = (msg->facility << 3) | msg->level;
-
-	if (syslog) {
-		if (buf) {
-			len += sprintf(buf, "<%u>", prefix);
-		} else {
-			len += 3;
-			if (prefix > 999)
-				len += 3;
-			else if (prefix > 99)
-				len += 2;
-			else if (prefix > 9)
-				len++;
-		}
-	}
 
-	len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
+	if (syslog)
+		len = print_syslog((msg->facility << 3) | msg->level, buf);
+	if (time)
+		len += print_time(msg->ts_nsec, buf + len);
 	return len;
 }
 
-static size_t msg_print_text(const struct printk_log *msg, bool syslog, char *buf, size_t size)
+static size_t msg_print_text(const struct printk_log *msg, bool syslog,
+			     bool time, char *buf, size_t size)
 {
 	const char *text = log_text(msg);
 	size_t text_size = msg->text_len;
 	size_t len = 0;
+	char prefix[PREFIX_MAX];
+	const size_t prefix_len = print_prefix(msg, syslog, time, prefix);
 
 	do {
 		const char *next = memchr(text, '\n', text_size);
@@ -1271,19 +1274,17 @@ static size_t msg_print_text(const struct printk_log *msg, bool syslog, char *bu
 		}
 
 		if (buf) {
-			if (print_prefix(msg, syslog, NULL) +
-			    text_len + 1 >= size - len)
+			if (prefix_len + text_len + 1 >= size - len)
 				break;
 
-			len += print_prefix(msg, syslog, buf + len);
+			memcpy(buf + len, prefix, prefix_len);
+			len += prefix_len;
 			memcpy(buf + len, text, text_len);
 			len += text_len;
 			buf[len++] = '\n';
 		} else {
 			/* SYSLOG_ACTION_* buffer size only calculation */
-			len += print_prefix(msg, syslog, NULL);
-			len += text_len;
-			len++;
+			len += prefix_len + text_len + 1;
 		}
 
 		text = next;
@@ -1318,9 +1319,17 @@ static int syslog_print(char __user *buf, int size)
 			break;
 		}
 
+		/*
+		 * To keep reading/counting partial line consistent,
+		 * use printk_time value as of the beginning of a line.
+		 */
+		if (!syslog_partial)
+			syslog_time = printk_time;
+
 		skip = syslog_partial;
 		msg = log_from_idx(syslog_idx);
-		n = msg_print_text(msg, true, text, LOG_LINE_MAX + PREFIX_MAX);
+		n = msg_print_text(msg, true, syslog_time, text,
+				   LOG_LINE_MAX + PREFIX_MAX);
 		if (n - syslog_partial <= size) {
 			/* message fits into buffer, move forward */
 			syslog_idx = log_next(syslog_idx);
@@ -1360,11 +1369,13 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	u64 next_seq;
 	u64 seq;
 	u32 idx;
+	bool time;
 
 	text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
 	if (!text)
 		return -ENOMEM;
 
+	time = printk_time;
 	logbuf_lock_irq();
 	/*
 	 * Find first record that fits, including all following records,
@@ -1375,7 +1386,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	while (seq < log_next_seq) {
 		struct printk_log *msg = log_from_idx(idx);
 
-		len += msg_print_text(msg, true, NULL, 0);
+		len += msg_print_text(msg, true, time, NULL, 0);
 		idx = log_next(idx);
 		seq++;
 	}
@@ -1386,7 +1397,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	while (len > size && seq < log_next_seq) {
 		struct printk_log *msg = log_from_idx(idx);
 
-		len -= msg_print_text(msg, true, NULL, 0);
+		len -= msg_print_text(msg, true, time, NULL, 0);
 		idx = log_next(idx);
 		seq++;
 	}
@@ -1397,14 +1408,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	len = 0;
 	while (len >= 0 && seq < next_seq) {
 		struct printk_log *msg = log_from_idx(idx);
-		int textlen;
-
-		textlen = msg_print_text(msg, true, text,
+		int textlen = msg_print_text(msg, true, time, text,
 					     LOG_LINE_MAX + PREFIX_MAX);
-		if (textlen < 0) {
-			len = textlen;
-			break;
-		}
+
 		idx = log_next(idx);
 		seq++;
 
@@ -1528,11 +1534,14 @@ int do_syslog(int type, char __user *buf, int len, int source)
 		} else {
 			u64 seq = syslog_seq;
 			u32 idx = syslog_idx;
+			bool time = syslog_partial ? syslog_time : printk_time;
 
 			while (seq < log_next_seq) {
 				struct printk_log *msg = log_from_idx(idx);
 
-				error += msg_print_text(msg, true, NULL, 0);
+				error += msg_print_text(msg, true, time, NULL,
+							0);
+				time = printk_time;
 				idx = log_next(idx);
 				seq++;
 			}
@@ -1935,21 +1944,6 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 }
 EXPORT_SYMBOL(vprintk);
 
-asmlinkage int printk_emit(int facility, int level,
-			   const char *dict, size_t dictlen,
-			   const char *fmt, ...)
-{
-	va_list args;
-	int r;
-
-	va_start(args, fmt);
-	r = vprintk_emit(facility, level, dict, dictlen, fmt, args);
-	va_end(args);
-
-	return r;
-}
-EXPORT_SYMBOL(printk_emit);
-
 int vprintk_default(const char *fmt, va_list args)
 {
 	int r;
@@ -2005,6 +1999,7 @@ EXPORT_SYMBOL(printk);
 
 #define LOG_LINE_MAX		0
 #define PREFIX_MAX		0
+#define printk_time		false
 
 static u64 syslog_seq;
 static u32 syslog_idx;
@@ -2028,8 +2023,8 @@ static void console_lock_spinning_enable(void) { }
 static int console_lock_spinning_disable_and_check(void) { return 0; }
 static void call_console_drivers(const char *ext_text, size_t ext_len,
 				 const char *text, size_t len) {}
-static size_t msg_print_text(const struct printk_log *msg,
-			     bool syslog, char *buf, size_t size) { return 0; }
+static size_t msg_print_text(const struct printk_log *msg, bool syslog,
+			     bool time, char *buf, size_t size) { return 0; }
 static bool suppress_message_printing(int level) { return false; }
 
 #endif /* CONFIG_PRINTK */
@@ -2387,8 +2382,7 @@ void console_unlock(void)
 
 		len += msg_print_text(msg,
 				console_msg_format & MSG_FORMAT_SYSLOG,
-				text + len,
-				sizeof(text) - len);
+				printk_time, text + len, sizeof(text) - len);
 		if (nr_ext_console_drivers) {
 			ext_len = msg_print_ext_header(ext_text,
 						sizeof(ext_text),
@@ -3112,7 +3106,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 		goto out;
 
 	msg = log_from_idx(dumper->cur_idx);
-	l = msg_print_text(msg, syslog, line, size);
+	l = msg_print_text(msg, syslog, printk_time, line, size);
 
 	dumper->cur_idx = log_next(dumper->cur_idx);
 	dumper->cur_seq++;
@@ -3183,6 +3177,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	u32 next_idx;
 	size_t l = 0;
 	bool ret = false;
+	bool time = printk_time;
 
 	if (!dumper->active)
 		goto out;
@@ -3206,7 +3201,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	while (seq < dumper->next_seq) {
 		struct printk_log *msg = log_from_idx(idx);
 
-		l += msg_print_text(msg, true, NULL, 0);
+		l += msg_print_text(msg, true, time, NULL, 0);
 		idx = log_next(idx);
 		seq++;
 	}
@@ -3217,7 +3212,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	while (l > size && seq < dumper->next_seq) {
 		struct printk_log *msg = log_from_idx(idx);
 
-		l -= msg_print_text(msg, true, NULL, 0);
+		l -= msg_print_text(msg, true, time, NULL, 0);
 		idx = log_next(idx);
 		seq++;
 	}
@@ -3230,7 +3225,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	while (seq < dumper->next_seq) {
 		struct printk_log *msg = log_from_idx(idx);
 
-		l += msg_print_text(msg, syslog, buf + l, size - l);
+		l += msg_print_text(msg, syslog, time, buf + l, size - l);
 		idx = log_next(idx);
 		seq++;
 	}