Re: [BUG]: when printk too more through serial, cpu up is failed.

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Mar 14, 2013 at 09:51:34PM +0800, Shuge wrote:
> Hi all,
>     When the kernel printk too many log, the cpu is failed to come online.
> The problem is this:
> For example, cpu0 bring up cpu1:
> 
>       a. cpu0 call cpu_up:
>          cpu_up()
>          ->_cpu_up()
>             ->__cpu_notify(CPU_UP_PREPARE)
>             ->__cpu_up()
>                ->boot_secondary()
> #       ->wait_for_completion_timeout(&cpu_running, msecs_to_jiffires(1000))
>          -> if (!cpu_online(cpu)) {
>                   pr_crit("CPU%u: failed to come online\n", cpu);
>                   ret = -EIO;
>               }
>          ->cpu_notify(CPU_ONLINE)
> 
>       b. cpu1 enter kernel:
>       secondary_start_kernel()
> @   ->printk("CPU%u: Booted secondary processor\n", cpu)
> *   ->calibrate_delay()
>       ->set_cpu_online()
>       ->complete(cpu_running)
>         ->cpumask_set_cpu()
> 
>    While cpu0 run to mark #,  which wait that cpu1 complete
> cpu_running, and set online.
> Generally, cpu0 can get it. But if the __log_buf is too large or
> other threads write
> it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is
> busy outputing
> buffer, which cost time more than 1s, and cpu1 have not join in
> sched, so cpu0 wait it timeout.
>    By reading printk.c, I found that can_use_console() always return
> true, which be called by
> console_trylock_for_printk(). Because, have_callable_console()
> return ture always, if the console
> driver set CON_ANYTIME flag. I think that cpu should not output the
> __log_buf in coming online,
> even though have_callable_console() is true.
> 
> /*
>  * Can we actually use the console at this time on this cpu?
>  *
>  * Console drivers may assume that per-cpu resources have
>  * been allocated. So unless they're explicitly marked as
>  * being able to cope (CON_ANYTIME) don't call them until
>  * this CPU is officially up.
>  */
> static inline int can_use_console(unsigned int cpu)
> {
>     return cpu_online(cpu) || have_callable_console();
> }
> 
> In can_use_console, why not is &&, but ||?
> 
> Kernel Version: 3.3.0

Why such an old and obsolete kernel version?  Please try this on 3.8,
lots of work have gone into the printk area that should have solved this
issue.

greg k-h