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From: Shilimkar, Santosh on 29 Jun 2010 05:00
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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From: Shilimkar, Santosh on 1 Jul 2010 00:30
(Adding linux-pm(a)lists.linux-foundation.org)

> -----Original Message-----
> From: Shilimkar, Santosh
> Sent: Tuesday, June 29, 2010 2:22 PM
> To: 'Kevin Cernekee'
> Cc: linux-kernel(a)vger.kernel.org; Russell King - ARM Linux
> 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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