linux-kernel - [PATCH 2/2] printk: make sure to print log on console.

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Message-Id: <20180531102246epcas5p2f1cbc6ff217172e12e2f78bb88eb4a7e~zs5h59tMh2250222502epcas5p2S@epcas5p2.samsung.com>
Date:   Thu, 31 May 2018 15:49:11 +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 2/2] printk: make sure to print log on console.

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

@why
In case of async printk, printk thread can miss logs because it checks
current log level at time of console_unlock.

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

Now if printk thread is scheduled after setting console loglevel
to silent, then user's requirement will be in waste, because it will not
print logs on console at time of printk thread scheduling.

@how
use one bit of flags field to store whether its console print
or not(console_print) by checking current console loglevel with 
message's level at time of log.
At time of print check this flag for printing message on console.

Signed-off-by: Vaneet Narang <v.narang@...sung.com>
Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
---
 kernel/printk/printk.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ab15903..4e0be66e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -360,8 +360,16 @@ struct printk_log {
 	u16 text_len;		/* length of text buffer */
 	u16 dict_len;		/* length of dictionary buffer */
 	u8 facility;		/* syslog facility */
-	u8 flags:5;		/* internal record flags */
+	u8 flags:4;		/* internal record flags */
 	u8 level:3;		/* syslog level */
+	/*
+	 * whether to print this msg on console or not?
+	 * due to async printk, printk thread can miss
+	 * prints at the time of console_flush because of
+	 * change in print level afterwards.
+	 */
+	u8 console_print:1;
+
 }
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 __packed __aligned(4)
@@ -623,7 +631,12 @@ static int log_store(int facility, int level,
 	msg->dict_len = dict_len;
 	msg->facility = facility;
 	msg->level = level & 7;
-	msg->flags = flags & 0x1f;
+	if (msg->level >= console_loglevel)
+		msg->console_print = 0;
+	else
+		msg->console_print = 1;
+
+	msg->flags = flags & 0xf;
 	if (ts_nsec > 0)
 		msg->ts_nsec = ts_nsec;
 	else
@@ -1144,9 +1157,9 @@ static int __init ignore_loglevel_setup(char *str)
 MODULE_PARM_DESC(ignore_loglevel,
 		 "ignore loglevel setting (prints all kernel messages to the console)");
 
-static bool suppress_message_printing(int level)
+static bool suppress_message_printing(int console_print)
 {
-	return (level >= console_loglevel && !ignore_loglevel);
+	return (!console_print && !ignore_loglevel);
 }
 
 #ifdef CONFIG_BOOT_PRINTK_DELAY
@@ -1172,13 +1185,13 @@ static int __init boot_delay_setup(char *str)
 }
 early_param("boot_delay", boot_delay_setup);
 
-static void boot_delay_msec(int level)
+static void boot_delay_msec(int console_print)
 {
 	unsigned long long k;
 	unsigned long timeout;
 
 	if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
-		|| suppress_message_printing(level)) {
+		|| suppress_message_printing(console_print)) {
 		return;
 	}
 
@@ -1199,7 +1212,7 @@ static void boot_delay_msec(int level)
 	}
 }
 #else
-static inline void boot_delay_msec(int level)
+static inline void boot_delay_msec(int console_print)
 {
 }
 #endif
@@ -1840,7 +1853,7 @@ asmlinkage int vprintk_emit(int facility, int level,
 		in_sched = true;
 	}
 
-	boot_delay_msec(level);
+	boot_delay_msec(level < console_loglevel);
 	printk_delay();
 
 	/* This stops the holder of console_sem just where we want him */
@@ -2011,7 +2024,7 @@ 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 bool suppress_message_printing(int level) { return false; }
+static bool suppress_message_printing(int console_print) { return false; }
 
 #endif /* CONFIG_PRINTK */
 
@@ -2354,7 +2367,7 @@ void console_unlock(void)
 			break;
 
 		msg = log_from_idx(console_idx);
-		if (suppress_message_printing(msg->level)) {
+		if (suppress_message_printing(msg->console_print)) {
 			/*
 			 * Skip record we have buffered and already printed
 			 * directly to the console when we received it, and
-- 
1.9.1