linux-kernel - [PATCH v2] printk: make sure to print log on console.

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Date:   Fri,  1 Jun 2018 14:26:42 +0530
From:   Maninder Singh <maninder1.s@...sung.com>
To:     pmladek@...e.com, sergey.senozhatsky@...il.com, rostedt@...dmis.org
Cc:     linux-kernel@...r.kernel.org, a.sahrawat@...sung.com,
        pankaj.m@...sung.com, v.narang@...sung.com,
        Maninder Singh <maninder1.s@...sung.com>
Subject: [PATCH v2] printk: make sure to print log on console.

This patch make sure printing of log on console if loglevel
at time of storing log is less than current console loglevel.

@why
In SMP printk can work asynchronously, logs can be missed on console
because it checks current log level at time of console_unlock,
not at time of storing logs.

func()
{
....
....
        console_verbose();  // user wants to have all the logs on console.
        pr_alert();
	dump_backtrace(); //prints with default loglevel.
        ...
        console_silent(); // stop all logs from printing on console.
}

Now if console_lock was owned by another process, the messages might
be handled after the consoles were silenced.

reused flag LOG_NOCONS as its usage is gone long back.
(5c2992ee7fd8a29d04125dc0aa3522784c5fa5eb)

Signed-off-by: Vaneet Narang <v.narang@...sung.com>
Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
---
v1 -> v2: make changes simpler as suggested by Petr Mladek.
	  use flag rather than changing structure of printk.

 kernel/printk/printk.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2f4af21..4b059fe 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -349,7 +349,7 @@ enum con_msg_format_flags {
  */
 
 enum log_flags {
-	LOG_NOCONS	= 1,	/* already flushed, do not print to console */
+	LOG_NOCONS	= 1,	/* suppress print, do not print to console */
 	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 */
@@ -1886,6 +1886,9 @@ asmlinkage int vprintk_emit(int facility, int level,
 	if (dict)
 		lflags |= LOG_PREFIX|LOG_NEWLINE;
 
+	if (suppress_message_printing(level))
+		lflags |= LOG_NOCONS;
+
 	printed_len = log_output(facility, level, lflags, dict, dictlen, text, text_len);
 
 	logbuf_unlock_irqrestore(flags);
@@ -2355,11 +2358,10 @@ void console_unlock(void)
 			break;
 
 		msg = log_from_idx(console_idx);
-		if (suppress_message_printing(msg->level)) {
+		if (msg->flags & LOG_NOCONS) {
 			/*
-			 * Skip record we have buffered and already printed
-			 * directly to the console when we received it, and
-			 * record that has level above the console loglevel.
+			 * Skip record if !ignore_loglevel, and
+			 * record has level above the console loglevel.
 			 */
 			console_idx = log_next(console_idx);
 			console_seq++;
-- 
1.9.1