printk: make sure to print log on console. (375899cd) · Commits · 戴 / test

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 by the commit ("printk: remove console flushing special cases for partial buffered lines"). Note that there are still some corner cases where this patch is not enough. For example, when the messages are flushed later from printk_safe buffers or when there are races between console_verbose() and console_silent() callers. Link: http://lkml.kernel.org/r/20180601090029epcas5p3cc93d4bfbebb3199f0a2684058da7e26~z-a_jkmrI2993329933epcas5p3q@epcas5p3.samsung.com Cc: linux-kernel@vger.kernel.org Cc: a.sahrawat@samsung.com Cc: pankaj.m@samsung.com Cc: v.narang@samsung.com Cc: <maninder1.s@samsung.com> Signed-off-by:

Vaneet Narang <v.narang@samsung.com> Signed-off-by:

Maninder Singh <maninder1.s@samsung.com> Reviewed-by:

Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by:

Petr Mladek <pmladek@suse.com>

kernel/printk/printk.c

+7 −5

Original line number	Original line	Diff line number	Diff line
	@@ -349,7 +349,7 @@ static int console_msg_format = MSG_FORMAT_DEFAULT;
	*/		*/

	enum log_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_NEWLINE = 2, /* text ended with a newline */
	LOG_PREFIX = 4, /* text started with a prefix */		LOG_PREFIX = 4, /* text started with a prefix */
	LOG_CONT = 8, /* text is a fragment of a continuation line */		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)		if (dict)
	lflags \|= LOG_PREFIX\|LOG_NEWLINE;		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);		printed_len = log_output(facility, level, lflags, dict, dictlen, text, text_len);

	logbuf_unlock_irqrestore(flags);		logbuf_unlock_irqrestore(flags);
	@@ -2349,11 +2352,10 @@ skip:
	break;		break;

	msg = log_from_idx(console_idx);		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		* Skip record if !ignore_loglevel, and
	* directly to the console when we received it, and		* record has level above the console loglevel.
	* record that has level above the console loglevel.
	*/		*/
	console_idx = log_next(console_idx);		console_idx = log_next(console_idx);
	console_seq++;		console_seq++;

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