On Thu, 3 Jun 2010 22:11:25 -0700 Kevin Cernekee <cernekee@xxxxxxxxx> wrote: > [Changes from v2: > > Use hotcpu_notifier - fix will only apply to hotplug events, not > initial SMP boot > > Kerneldocify function arguments > > Use acquire_console_sem() instead of try_acquire_console_sem() > > Reuse the existing disable_boot_consoles() initcall instead of making a > new one] > > 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. > > ... > > +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 *console) > } > 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(void) > unregister_console(con); > } > } > + register_hotcpu_notifier(&console_nb); gack, we seem to have made these interfaces as hard to use and as documentation-free as we possibly could :( This: --- a/kernel/printk.c~printk-fix-delayed-messages-from-cpu-hotplug-events-fix +++ a/kernel/printk.c @@ -1009,10 +1009,6 @@ static int __cpuinit console_cpu_notify( 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. * @@ -1411,7 +1407,7 @@ static int __init printk_late_init(void) unregister_console(con); } } - register_hotcpu_notifier(&console_nb); + hotcpu_notifier(console_cpu_notify, 0); return 0; } late_initcall(printk_late_init); There are numerous other register_hotcpu_notifier() callsites which can probably be converted.
