linux-kernel - [patch RFC 24/29] printk: Put seq and dropped into cons_text

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Date:   Sun, 11 Sep 2022 00:28:09 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helge Deller <deller@....de>,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        John Ogness <jogness@...utronix.de>
Subject: [patch RFC 24/29] printk: Put seq and dropped into cons_text_desc

Non-BKL consoles have atomic sequence tracking which is not
compatible with the legacy consoles.

Put sequence and dropped message count into struct cons_text_desc, let
cons_fill_outbuf() operate on the seq/dropped fields and let the call sites
handle the update to the corresponding fields in struct console.

This allows sharing cons_fill_outbuf() between the two worlds. For the
legacy consoles this is not more or less racy than the existing code.

Co-Developed-by: John Ogness <jogness@...utronix.de>
Signed-off-by: John Ogness <jogness@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 include/linux/console.h |    2 ++
 kernel/printk/printk.c  |   25 ++++++++++++++-----------
 2 files changed, 16 insertions(+), 11 deletions(-)

--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -232,6 +232,7 @@ struct cons_text_buf {
  * @txtbuf:		Pointer to buffer for storing the text
  * @outbuf:		Pointer to the position in @buffer for
  *			writing it out to the device
+ * @seq:		The sequence requested
  * @dropped:		The dropped count
  * @len:		Message length
  * @extmsg:		Select extended format printing
@@ -239,6 +240,7 @@ struct cons_text_buf {
 struct cons_outbuf_desc {
 	struct cons_text_buf	*txtbuf;
 	char			*outbuf;
+	u64			seq;
 	unsigned long		dropped;
 	unsigned int		len;
 	bool			extmsg;
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2740,7 +2740,7 @@ static void cons_print_dropped(struct co
  * If it is NULL then records have been dropped or skipped and con->seq
  * has been forwarded so the caller can try to print the next record.
  */
-static bool cons_fill_outbuf(struct console *con, struct cons_outbuf_desc *desc)
+static bool cons_fill_outbuf(struct cons_outbuf_desc *desc)
 {
 	static int panic_console_dropped;
 
@@ -2755,12 +2755,12 @@ static bool cons_fill_outbuf(struct cons
 
 	prb_rec_init_rd(&r, &info, txtbuf->text, CONSOLE_LOG_MAX);
 
-	if (!prb_read_valid(prb, con->seq, &r))
+	if (!prb_read_valid(prb, desc->seq, &r))
 		return false;
 
-	if (con->seq != r.info->seq) {
-		con->dropped += r.info->seq - con->seq;
-		con->seq = r.info->seq;
+	if (desc->seq != r.info->seq) {
+		desc->dropped += r.info->seq - desc->seq;
+		desc->seq = r.info->seq;
 		if (panic_in_progress() && panic_console_dropped++ > 10) {
 			suppress_panic_printk = 1;
 			pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
@@ -2769,7 +2769,7 @@ static bool cons_fill_outbuf(struct cons
 
 	/* Skip record that has level above the console loglevel. */
 	if (suppress_message_printing(r.info->level)) {
-		con->seq++;
+		desc->seq++;
 		return true;
 	}
 
@@ -2789,9 +2789,7 @@ static bool cons_fill_outbuf(struct cons
 
 		desc->len = len;
 		desc->outbuf = txtbuf->text;
-		desc->dropped = con->dropped;
 		cons_print_dropped(desc);
-		con->dropped = desc->dropped;
 	}
 
 	return true;
@@ -2820,16 +2818,21 @@ static bool console_emit_next_record(str
 				     bool *handover, bool extmsg)
 {
 	struct cons_outbuf_desc desc = {
-		.txtbuf	= txtbuf,
-		.extmsg = extmsg,
+		.txtbuf		= txtbuf,
+		.extmsg		= extmsg,
+		.seq		= con->seq,
+		.dropped	= con->dropped,
 	};
 	unsigned long flags;
 
 	*handover = false;
 
-	if (!cons_fill_outbuf(con, &desc))
+	if (!cons_fill_outbuf(&desc))
 		return false;
 
+	con->seq = desc.seq;
+	con->dropped = desc.dropped;
+
 	if (!desc.outbuf)
 		goto skip;