linux-kernel - [PATCH v2 1/2] printk: flush consoles before checking progress

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Message-Id: <20231006082151.6969-2-pmladek@suse.com>
Date:   Fri,  6 Oct 2023 10:21:50 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Todd Brandt <todd.e.brandt@...el.com>,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>
Subject: [PATCH v2 1/2] printk: flush consoles before checking progress

From: John Ogness <john.ogness@...utronix.de>

Commit 9e70a5e109a4 ("printk: Add per-console suspended state")
removed console lock usage during resume and replaced it with
the clearly defined console_list_lock and srcu mechanisms.

However, the console lock usage had an important side-effect
of flushing the consoles. After its removal, consoles were no
longer flushed before checking their progress.

Add the console_lock/console_unlock dance to the beginning
of __pr_flush() to actually flush the consoles before checking
their progress. Also add comments to clarify this additional
usage of the console lock.

Note that console_unlock() does not guarantee flushing all messages
since the commit dbdda842fe96f89 ("printk: Add console owner and waiter
logic to load balance console writes").

Reported-by: Todd Brandt <todd.e.brandt@...el.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217955
Fixes: 9e70a5e109a4 ("printk: Add per-console suspended state")
Co-developed-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/printk/printk.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7e0b4dd02398..0b3af1529778 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3740,12 +3740,18 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre

 	seq = prb_next_seq(prb);

+	/* Flush the consoles so that records up to @seq are printed. */
+	console_lock();
+	console_unlock();
+
 	for (;;) {
 		diff = 0;

 		/*
 		 * Hold the console_lock to guarantee safe access to
-		 * console->seq.
+		 * console->seq. Releasing console_lock flushes more
+		 * records in case @seq is still not printed on all
+		 * usable consoles.
 		 */
 		console_lock();

-- 
2.35.3