linux-kernel - [PATCH 1/2] printk: Relocate wake_klogd check close to the end of console

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Message-ID: <20171102135146.GN3252168@devbig577.frc2.facebook.com>
Date:   Thu, 2 Nov 2017 06:51:46 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH 1/2] printk: Relocate wake_klogd check close to the end of
 console_unlock()

We mark for waking up klogd whenever we see a new message sequence in
the main loop.  However, the actual wakeup is always at the end of the
function and we can easily test for the wakeup condition when we do
the final should-we-repeat check.

Move the wake_klogd condition check out of the main loop.  This avoids
doing the same thing repeatedly and groups similar checks into a
common place.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/printk/printk.c |   17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2184,10 +2184,6 @@ again:
 
 		printk_safe_enter_irqsave(flags);
 		raw_spin_lock(&logbuf_lock);
-		if (seen_seq != log_next_seq) {
-			wake_klogd = true;
-			seen_seq = log_next_seq;
-		}
 
 		if (console_seq < log_first_seq) {
 			len = sprintf(text, "** %u printk messages dropped ** ",
@@ -2248,12 +2244,17 @@ skip:
 	up_console_sem();
 
 	/*
-	 * Someone could have filled up the buffer again, so re-check if there's
-	 * something to flush. In case we cannot trylock the console_sem again,
-	 * there's a new owner and the console_unlock() from them will do the
-	 * flush, no worries.
+	 * Check whether userland needs notification.  Also, someone could
+	 * have filled up the buffer again, so re-check if there's
+	 * something to flush. In case we cannot trylock the console_sem
+	 * again, there's a new owner and the console_unlock() from them
+	 * will do the flush, no worries.
 	 */
 	raw_spin_lock(&logbuf_lock);
+	if (seen_seq != log_next_seq) {
+		wake_klogd = true;
+		seen_seq = log_next_seq;
+	}
 	retry = console_seq != log_next_seq;
 	raw_spin_unlock(&logbuf_lock);
 	printk_safe_exit_irqrestore(flags);