linux-kernel - Additional fix : (was [v2]printk: fix delayed messages from CPU hotplug events)

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Date:	Tue, 29 Jun 2010 14:22:26 +0530
From:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
To:	Kevin Cernekee <cernekee@...il.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Subject: Additional fix : (was [v2]printk: fix delayed messages from CPU
 hotplug events)

Hi,

I have faced similar issue as what is being described in below with
latest kernel.

------------------------------------------------
https://patchwork.kernel.org/patch/103347/

When a secondary CPU is being brought up, it is not uncommon for
printk() to be invoked when cpu_online(smp_processor_id()) == 0.  The
case that I witnessed personally was on MIPS:

http://lkml.org/lkml/2010/5/30/4

If (can_use_console() == 0), printk() will spool its output to log_buf
and it will be visible in "dmesg", but that output will NOT be echoed to
the console until somebody calls release_console_sem() from a CPU that
is online.  Therefore, the boot time messages from the new CPU can get
stuck in "limbo" for a long time, and might suddenly appear on the
screen when a completely unrelated event (e.g. "eth0: link is down")
occurs.

This patch modifies the console code so that any pending messages are
automatically flushed out to the console whenever a CPU hotplug
operation completes successfully or aborts.

-----------------------------------------------

Above patch fixes only half of the problem. I mean the cpu online
path prints are coming on the console.

But similar problem also exist if there are prints in the cpu offline
path. I got that fixed by adding below patch on top of you patch.

diff --git a/kernel/printk.c b/kernel/printk.c
index d370b74..f4d7352 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -982,6 +982,9 @@ static int __cpuinit console_cpu_notify(struct notifier_bloc
        switch (action) {
        case CPU_ONLINE:
        case CPU_UP_CANCELED:
+       case CPU_DEAD:
+       case CPU_DYING:
+       case CPU_DOWN_FAILED:
                if (try_acquire_console_sem() == 0)
                        release_console_sem();
        }

Regards
Santosh
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