linux-kernel - [PATCH 5.10-rt] printk: fix suppressed message print when reboot/panic

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Message-Id: <20220321053815.71316-1-schspa@gmail.com>
Date:   Mon, 21 Mar 2022 13:38:16 +0800
From:   Schspa Shi <schspa@...il.com>
To:     pmladek@...e.com, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, john.ogness@...utronix.de
Cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        bigeasy@...utronix.de, tglx@...utronix.de, schspa@...il.com
Subject: [PATCH 5.10-rt] printk: fix suppressed message print when reboot/panic

Update printk_seq for suppressed message.

Affects 5.9-rt and 5.10-rt

When message is suppressed, printk_seq should be updated, otherwise
this message will be printed when reboot. This problem was introduced
in commit 3edc0c85d154 ("printk: Rebase on top of new ring buffer").

Signed-off-by: Schspa Shi <schspa@...il.com>
---
 kernel/printk/printk.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 0c56873396a9..f68c4ba7eb4d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2826,8 +2826,17 @@ static int printk_kthread_func(void *data)
 		if (!(con->flags & CON_ENABLED))
 			continue;
 
-		if (suppress_message_printing(r.info->level))
+		printk_seq = atomic64_read(&con->printk_seq);
+
+		if (suppress_message_printing(r.info->level)) {
+			/*
+			 * 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.
+			 */
+			atomic64_cmpxchg_relaxed(&con->printk_seq, printk_seq, seq);
 			continue;
+		}
 
 		if (con->flags & CON_EXTENDED) {
 			len = info_print_ext_header(ext_text,
@@ -2843,7 +2852,6 @@ static int printk_kthread_func(void *data)
 				printk_time);
 		}
 
-		printk_seq = atomic64_read(&con->printk_seq);
 
 		console_lock();
 		console_may_schedule = 0;
-- 
2.29.0