diff options
author | Kevin Cernekee <cernekee@gmail.com> | 2010-08-03 12:58:22 +0530 |
---|---|---|
committer | Bryan Wu <bryan.wu@canonical.com> | 2010-08-26 21:23:45 +0800 |
commit | ff42318a50c7b0cc1c5bbdf2a6567fea80546fa4 (patch) | |
tree | 4eef15f362d91da472e141605449cce77005bafc /kernel | |
parent | 22b99ae035995c0a0e88638050ac64ad97bfc343 (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.
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@ti.com>
Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/printk.c | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/kernel/printk.c b/kernel/printk.c index 444b770c9595..14d7cc1eee06 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 |