The patch titled
printk: fix delayed messages from CPU hotplug events
has been added to the -mm tree. Its filename is
printk-fix-delayed-messages-from-cpu-hotplug-events.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: printk: fix delayed messages from CPU hotplug events
From: Kevin Cernekee <cernekee@xxxxxxxxx>
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.
The issue was seen on 2.6.34.
Signed-off-by: Kevin Cernekee <cernekee@xxxxxxxxx>
Reviewed-by: Paul Mundt <lethal@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/printk.c | 34 ++++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)
diff -puN kernel/printk.c~printk-fix-delayed-messages-from-cpu-hotplug-events kernel/printk.c
--- a/kernel/printk.c~printk-fix-delayed-messages-from-cpu-hotplug-events
+++ a/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 +987,33 @@ void resume_console(void)
}
/**
+ * console_cpu_notify - print deferred console messages after CPU hotplug
+ * @self: notifier struct
+ * @action: CPU hotplug event
+ * @hcpu: unused
+ *
+ * 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 fails to come up), 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_UP_CANCELED:
+ acquire_console_sem();
+ release_console_sem();
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata console_nb = {
+ .notifier_call = console_cpu_notify,
+};
+
+/**
* acquire_console_sem - lock the console system for exclusive use.
*
* Acquires a semaphore which guarantees that the caller has
@@ -1371,7 +1400,7 @@ int unregister_console(struct console *c
}
EXPORT_SYMBOL(unregister_console);
-static int __init disable_boot_consoles(void)
+static int __init printk_late_init(void)
{
struct console *con;
@@ -1382,9 +1411,10 @@ static int __init disable_boot_consoles(
unregister_console(con);
}
}
+ register_hotcpu_notifier(&console_nb);
return 0;
}
-late_initcall(disable_boot_consoles);
+late_initcall(printk_late_init);
#if defined CONFIG_PRINTK
_
Patches currently in -mm which might be from cernekee@xxxxxxxxx are
printk-fix-delayed-messages-from-cpu-hotplug-events.patch
printk-fix-delayed-messages-from-cpu-hotplug-events-fix.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
