Messages in this thread Patch in this message | | | From | "Shilimkar, Santosh" <> | Date | Tue, 3 Aug 2010 22:23:45 +0530 | Subject | RE: Additional fix : (was [v2]printk: fix delayed messages from CPU hotplug events) |
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> -----Original Message----- > From: Randy Dunlap [mailto:rdunlap@xenotime.net] > Sent: Tuesday, August 03, 2010 8:55 PM > To: Shilimkar, Santosh > Cc: Andrew Morton; Kevin Cernekee; linux-kernel@vger.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@ti.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@ti.com> Signed-off-by: Kevin Cernekee <cernekee@gmail.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 [unhandled content-type:application/octet-stream] | |