Subject: Re: mmotm 2014-04-24-13-07 uploaded

From: "Paul E. McKenney" <[email-masked]>
Date: Sun, 27 Apr 2014 17:26:15 -0700

On Sun, Apr 27, 2014 at 01:40:17PM -0700, Randy Dunlap wrote:
> 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 <[email-masked]> 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 <[email-masked]
> >>>>> ---
> >>>>>  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 <[email-masked]>
> >> [ paulmck: Fix TINY_RCU build error. ]
> >> Signed-off-by: Paul E. McKenney <[email-masked]>
> 
> I guess that you want static inline on those functions...

Indeed I do, please see the subsequent patch.

One of my favorite mistakes, leaving out static inline...

							Thanx, Paul

> > 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
>