path: root/kernel
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authorKevin Cernekee <cernekee@gmail.com>2010-06-03 22:11:25 -0700
committerRalf Baechle <ralf@linux-mips.org>2010-08-05 13:25:59 +0100
commit034260d6779087431a8b2f67589c68b919299e5c (patch)
tree9d9f1def96651ae098c87687a640079ddd2aafd4 /kernel
parentd745866e4d8c0675bab90868b5e4a8fcd053eff2 (diff)
printk: fix delayed 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. The issue was seen on 2.6.34. Original patch by Kevin Cernekee with cleanups by akpm and additional fixes by Santosh Shilimkar. This patch superseeds https://patchwork.linux-mips.org/patch/1357/. Signed-off-by: Kevin Cernekee <cernekee@gmail.com> To: <mingo@elte.hu> To: <akpm@linux-foundation.org> To: <simon.kagstrom@netinsight.net> To: <David.Woodhouse@intel.com> To: <lethal@linux-sh.org> Cc: <linux-kernel@vger.kernel.org> Cc: <linux-mips@linux-mips.org> Reviewed-by: Paul Mundt <lethal@linux-sh.org> Signed-off-by: Kevin Cernekee <cernekee@gmail.com> Patchwork: https://patchwork.linux-mips.org/patch/1534/ LKML-Reference: <ede63b5a20af951c755736f035d1e787772d7c28@localhost> LKML-Reference: <EAF47CD23C76F840A9E7FCE10091EFAB02C5DB6D1F@dbde02.ent.ti.com> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'kernel')
1 files changed, 31 insertions, 2 deletions
diff --git a/kernel/printk.c b/kernel/printk.c
index 444b770c959..4ab0164bcf8 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 +987,32 @@ 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_DEAD:
+ case CPU_DYING:
+ acquire_console_sem();
+ release_console_sem();
+ }
+ return NOTIFY_OK;
* acquire_console_sem - lock the console system for exclusive use.
* Acquires a semaphore which guarantees that the caller has
@@ -1371,7 +1399,7 @@ int unregister_console(struct console *console)
-static int __init disable_boot_consoles(void)
+static int __init printk_late_init(void)
struct console *con;
@@ -1382,9 +1410,10 @@ static int __init disable_boot_consoles(void)
+ hotcpu_notifier(console_cpu_notify, 0);
return 0;
#if defined CONFIG_PRINTK