linux-kernel - Re: [PATCH 2/2] printk: Provide a wake_up

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Date:	Thu, 14 Mar 2013 18:24:22 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	James Hogan <james.hogan@...tec.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] printk: Provide a wake_up_klogd() off-case

On Thu, Mar 14, 2013 at 4:39 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Thu, 14 Mar 2013 15:26:29 +0100 Frederic Weisbecker <fweisbec@...il.com> wrote:
>
>> wake_up_klogd() is useless when CONFIG_PRINTK=n because
>> neither printk() nor printk_sched() are in use and there
>> are actually no waiter on log_wait waitqueue. It should
>> be a stub in this case for users like bust_spinlocks().
>>
>> Otherwise this results in this warning when CONFIG_PRINTK=n
>> and CONFIG_IRQ_WORK=n:
>>
>>       kernel/built-in.o In function `wake_up_klogd':
>>       (.text.wake_up_klogd+0xb4): undefined reference to `irq_work_queue'
>>
>> To fix this, provide an off-case for wake_up_klogd() when
>> CONFIG_PRINTK=n.
>>
>> There is much more from console_unlock() and other console
>> related code in printk.c that should be moved under
>> CONFIG_PRINTK. But for now, focus on a minimal fix as we passed
>> the merged window already.
>>
>> --- a/include/linux/kernel.h
>> +++ b/include/linux/kernel.h
>> @@ -390,7 +390,6 @@ extern struct pid *session_of_pgrp(struct pid *pgrp);
>>  unsigned long int_sqrt(unsigned long);
>>
>>  extern void bust_spinlocks(int yes);
>> -extern void wake_up_klogd(void);
>>  extern int oops_in_progress;         /* If set, an oops, panic(), BUG() or die() is in progress */
>>  extern int panic_timeout;
>>  extern int panic_on_oops;
>> diff --git a/include/linux/printk.h b/include/linux/printk.h
>> index 1249a54..822171f 100644
>> --- a/include/linux/printk.h
>> +++ b/include/linux/printk.h
>> @@ -134,6 +134,8 @@ extern int printk_delay_msec;
>>  extern int dmesg_restrict;
>>  extern int kptr_restrict;
>>
>> +extern void wake_up_klogd(void);
>> +
>
> Given this, it would be prudent to include printk.h in
> bust_spinlocks.c.  printk.h currently gets included by kernel.h, but
> that doesn't actually seem necessary - nothing in kernel.h calls
> printk().
>
> (I pity anyone who tries to remove that include from kernel.h ;))

Why did you have to say that?  Now I'm inclined to poke at it and
just see how bad it really is when I pull on that loose thread...

P.
--

>
> --- a/lib/bust_spinlocks.c~printk-provide-a-wake_up_klogd-off-case-fix
> +++ a/lib/bust_spinlocks.c
> @@ -8,6 +8,7 @@
>   */
>
>  #include <linux/kernel.h>
> +#include <linux/printk.h>
>  #include <linux/spinlock.h>
>  #include <linux/tty.h>
>  #include <linux/wait.h>
> @@ -28,5 +29,3 @@ void __attribute__((weak)) bust_spinlock
>                         wake_up_klogd();
>         }
>  }
> -
> -
> _
>
> --
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