linux-kernel - Re: mmotm 2014-04-24-13-07 uploaded

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Message-ID: <535D6B31.3040604@infradead.org>
Date:	Sun, 27 Apr 2014 13:40:17 -0700
From:	Randy Dunlap <rdunlap@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
CC:	Rik van Riel <riel@...hat.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Richard Weinberger <richard@....at>,
	linux-next@...r.kernel.org, umgwanakikbuti@...il.com
Subject: Re: mmotm 2014-04-24-13-07 uploaded

On 04/27/14 10:27, Randy Dunlap wrote:
> On 04/26/14 23:26, Paul E. McKenney wrote:
>> On Fri, Apr 25, 2014 at 01:52:30PM -0700, Randy Dunlap wrote:
>>> On 04/25/14 13:44, Randy Dunlap wrote:
>>>> On 04/25/14 07:04, Rik van Riel wrote:
>>>>> On Thu, 24 Apr 2014 15:40:29 -0700
>>>>> Randy Dunlap <rdunlap@...radead.org> wrote:
>>>>>
>>>>>
>>>>>> uml on x86_64 defconfig:
>>>>>>
>>>>>> drivers/built-in.o: In function `__handle_sysrq':
>>>>>> drivers/tty/sysrq.c:514: undefined reference to `rcu_sysrq_start'
>>>>>> drivers/tty/sysrq.c:558: undefined reference to `rcu_sysrq_end'
>>>>>
>>>>> Randy, does the patch below fix it?
>>>
>>> CONFIG_TINY_RCU=y
>>>
>>> tiny.c does not provide these functions...  Paul...
>>>
>>>> Hm, no, it does not.  I'll look into it.
>>>>
>>>>> Mike, this patch should also address your concerns.
>>>>>
>>>>> Andrew, this can be a -fix patch for the sysctl-rcu patch,
>>>>> assuming it fixes things :)
>>>>>
>>>>> Signed-off-by: Rik van Riel <riel@...hat.com
>>>>> ---
>>>>>  drivers/tty/sysrq.c | 1 +
>>>>>  kernel/rcu/update.c | 3 ++-
>>>>>  2 files changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
>>>>> index dd53af9..0867433 100644
>>>>> --- a/drivers/tty/sysrq.c
>>>>> +++ b/drivers/tty/sysrq.c
>>>>> @@ -46,6 +46,7 @@
>>>>>  #include <linux/jiffies.h>
>>>>>  #include <linux/syscalls.h>
>>>>>  #include <linux/of.h>
>>>>> +#include <linux/rcupdate.h>
>>>>>  
>>>>>  #include <asm/ptrace.h>
>>>>>  #include <asm/irq_regs.h>
>>>>> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
>>>>> index 2ac3289..d22309c 100644
>>>>> --- a/kernel/rcu/update.c
>>>>> +++ b/kernel/rcu/update.c
>>>>> @@ -322,7 +322,8 @@ int rcu_jiffies_till_stall_check(void)
>>>>>  
>>>>>  void rcu_sysrq_start(void)
>>>>>  {
>>>>> -	rcu_cpu_stall_suppress = 2;
>>>>> +	if (!rcu_cpu_stall_suppress)
>>>>> +		rcu_cpu_stall_suppress = 2;
>>>>>  }
>>>>>  
>>>>>  void rcu_sysrq_end(void)
>>
>> You would think that I would have learned by now that RCU requires a bit
>> more care...  Anyway, patch containing only the APIs that -should- work
>> is below.  Currently testing it on the usual set of configs.
>>
>> 							Thanx, Paul
>>
>> ------------------------------------------------------------------------
>>
>> rcu: Provide API to suppress stall warnings while sysrc runs
>>
>> Some sysrq handlers can run for a long time, because they dump a lot
>> of data onto a serial console. Having RCU stall warnings pop up in
>> the middle of them only makes the problem worse.
>>
>> This commit provides rcu_sysrq_start() and rcu_sysrq_end() APIs to
>> temporarily suppress RCU CPU stall warnings while a sysrq request is
>> handled.
>>
>> Signed-off-by: Rik van Riel <riel@...hat.com>
>> [ paulmck: Fix TINY_RCU build error. ]
>> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

I guess that you want static inline on those functions...


> Still on uml on x86_64 defconfig:
> 
>   LD      init/built-in.o
> init/version.o: In function `rcu_sysrq_start':
> include/linux/rcupdate.h:258: multiple definition of `rcu_sysrq_start'
> init/main.o:include/linux/rcupdate.h:258: first defined here
> init/version.o: In function `rcu_sysrq_end':
> include/linux/rcupdate.h:261: multiple definition of `rcu_sysrq_end'
> init/main.o:include/linux/rcupdate.h:261: first defined here
> init/mounts.o: In function `rcu_sysrq_start':
> include/linux/rcupdate.h:258: multiple definition of `rcu_sysrq_start'
> init/main.o:include/linux/rcupdate.h:258: first defined here
> init/mounts.o: In function `rcu_sysrq_end':
> include/linux/rcupdate.h:261: multiple definition of `rcu_sysrq_end'
> init/main.o:include/linux/rcupdate.h:261: first defined here
> init/noinitramfs.o: In function `rcu_sysrq_start':
> include/linux/rcupdate.h:258: multiple definition of `rcu_sysrq_start'
> init/main.o:include/linux/rcupdate.h:258: first defined here
> init/noinitramfs.o: In function `rcu_sysrq_end':
> include/linux/rcupdate.h:261: multiple definition of `rcu_sysrq_end'
> init/main.o:include/linux/rcupdate.h:261: first defined here
> init/init_task.o: In function `rcu_sysrq_start':
> include/linux/rcupdate.h:258: multiple definition of `rcu_sysrq_start'
> init/main.o:include/linux/rcupdate.h:258: first defined here
> init/init_task.o: In function `rcu_sysrq_end':
> include/linux/rcupdate.h:261: multiple definition of `rcu_sysrq_end'
> init/main.o:include/linux/rcupdate.h:261: first defined here
> make[2]: *** [init/built-in.o] Error 1
> 
> 
> 
>>
>> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
>> index a6f2664a1b77..3f53c96b3b77 100644
>> --- a/include/linux/rcupdate.h
>> +++ b/include/linux/rcupdate.h
>> @@ -248,6 +248,18 @@ void rcu_idle_exit(void);
>>  void rcu_irq_enter(void);
>>  void rcu_irq_exit(void);
>>  
>> +#ifdef CONFIG_RCU_STALL_COMMON
>> +void rcu_sysrq_start(void);
>> +void rcu_sysrq_end(void);
>> +#else /* #ifdef CONFIG_RCU_STALL_COMMON */
>> +void rcu_sysrq_start(void)
>> +{
>> +}
>> +void rcu_sysrq_end(void)
>> +{
>> +}
>> +#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
>> +
>>  #ifdef CONFIG_RCU_USER_QS
>>  void rcu_user_enter(void);
>>  void rcu_user_exit(void);
>> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
>> index ed7a0d72562c..a2aeb4df0f60 100644
>> --- a/kernel/rcu/update.c
>> +++ b/kernel/rcu/update.c
>> @@ -320,6 +320,18 @@ int rcu_jiffies_till_stall_check(void)
>>  	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
>>  }
>>  
>> +void rcu_sysrq_start(void)
>> +{
>> +	if (!rcu_cpu_stall_suppress)
>> +		rcu_cpu_stall_suppress = 2;
>> +}
>> +
>> +void rcu_sysrq_end(void)
>> +{
>> +	if (rcu_cpu_stall_suppress == 2)
>> +		rcu_cpu_stall_suppress = 0;
>> +}
>> +
>>  static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
>>  {
>>  	rcu_cpu_stall_suppress = 1;
>>
> 
> 


-- 
~Randy
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