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

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Date:	Thu, 14 Mar 2013 23:34:46 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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

2013/3/14 Paul Gortmaker <paul.gortmaker@...driver.com>:
> 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...

$ git grep "#include <linux/printk.h>" | cut -d: -f1 | uniq | wc -l
29

$ git grep printk | cut -d: -f1 | uniq | wc -l
6689

There is roughly 6689 - 29 = 6660 files to modify :)
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