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

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Message-ID: <EAF47CD23C76F840A9E7FCE10091EFAB02C641DD23@dbde02.ent.ti.com>
Date:	Tue, 3 Aug 2010 22:23:45 +0530
From:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
To:	Randy Dunlap <rdunlap@...otime.net>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Kevin Cernekee <cernekee@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Subject: RE: Additional fix : (was [v2]printk: fix delayed messages from CPU
 hotplug events)

> -----Original Message-----
> From: Randy Dunlap [mailto:rdunlap@...otime.net]
> Sent: Tuesday, August 03, 2010 8:55 PM
> To: Shilimkar, Santosh
> Cc: Andrew Morton; Kevin Cernekee; linux-kernel@...r.kernel.org; Russell
> King - ARM Linux
> Subject: Re: Additional fix : (was [v2]printk: fix delayed messages from
> CPU hotplug events)
> 
> On Tue, 3 Aug 2010 13:03:25 +0530 Shilimkar, Santosh wrote:
> 

<snip>

> >  /**
> > + * console_cpu_notify - print deferred console messages after CPU
> hotplug
> > + *
> > + * If printk() is called from a CPU that is not online yet, the
> messages
> > + * will be spooled but will not show up on the console.  This function
> is
> > + * called when a new CPU comes online and ensures that any such output
> > + * gets printed.
> > + */
> > +static int __cpuinit console_cpu_notify(struct notifier_block *self,
> > +	unsigned long action, void *hcpu)
> > +{
> 
> 
> kernel-doc notation should include function parameters also, please.
> 
Sure. Here is an updated version.
--------------------------------------------
>From 127c0ea58982762ad194f22d1281baaf529c9cbc Mon Sep 17 00:00:00 2001
From: Santosh Shilimkar <santosh.shilimkar@...com>
Date: Tue, 3 Aug 2010 12:58:22 +0530
Subject: [PATCH v2] console: flush delayed log messages from cpu-hotplug events

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.
This is true even when CPU is getting hot-plugged out(offline) so
need to add additional hotplug events.

The issue was seen on 2.6.34.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@...com>
Signed-off-by: Kevin Cernekee <cernekee@...il.com>
---
 kernel/printk.c |   39 +++++++++++++++++++++++++++++++++++++++
 1 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index 444b770..c145cef 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -37,6 +37,8 @@
 #include <linux/ratelimit.h>
 #include <linux/kmsg_dump.h>
 #include <linux/syslog.h>
+#include <linux/cpu.h>
+#include <linux/notifier.h>
 
 #include <asm/uaccess.h>
 
@@ -985,6 +987,43 @@ void resume_console(void)
 }
 
 /**
+ * console_cpu_notify - print deferred console messages after CPU hotplug
+ * @self: pointer to notfier block
+ * @action: cpu-hotplug events
+ * @hcpu: void poniter to pass any data
+ *
+ * If printk() is called from a CPU that is not online yet, the messages
+ * will be spooled but will not show up on the console.  This function is
+ * called when a new CPU comes online or goes offline and ensures that
+ * any such output gets printed.
+ */
+static int __cpuinit console_cpu_notify(struct notifier_block *self,
+	unsigned long action, void *hcpu)
+{
+	switch (action) {
+	case CPU_ONLINE:
+	case CPU_DEAD:
+	case CPU_DYING:
+	case CPU_DOWN_FAILED:
+	case CPU_UP_CANCELED:
+		if (try_acquire_console_sem() == 0)
+			release_console_sem();
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata console_nb = {
+	.notifier_call		= console_cpu_notify,
+};
+
+static int __init console_notifier_init(void)
+{
+	register_cpu_notifier(&console_nb);
+	return 0;
+}
+late_initcall(console_notifier_init);
+
+/**
  * acquire_console_sem - lock the console system for exclusive use.
  *
  * Acquires a semaphore which guarantees that the caller has
-- 
1.6.0.4


Download attachment "console-flush-delayed-log-messages-from-cpu-hotplug_v2.patch" of type "application/octet-stream" (2975 bytes)