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Message-ID: <20080824170949.GG6851@linux.vnet.ibm.com>
Date: Sun, 24 Aug 2008 10:09:49 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Manfred Spraul <manfred@...orfullife.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC, PATCH] state machine based rcu
On Sat, Aug 23, 2008 at 10:16:17AM +0200, Manfred Spraul wrote:
> Paul E. McKenney wrote:
>>> -#if defined(CONFIG_PREEMPT_RCU) && defined(CONFIG_NO_HZ)
>>> +#ifdef CONFIG_NO_HZ
>>> extern void rcu_irq_enter(void);
>>> extern void rcu_irq_exit(void);
>>> #else
>>> # define rcu_irq_enter() do { } while (0)
>>> # define rcu_irq_exit() do { } while (0)
>>> -#endif /* CONFIG_PREEMPT_RCU */
>>> +#endif /* CONFIG_NO_HZ */
>>>
>>
>> Good approach! Will steal it. ;-)
>>
>>
> I've attached an updated patch [now without the initial "From" line. Either
> thunderbird or dovecot cannot handle that, sorry for the noise caused by
> posting everything 3 times].
No problem!
> Btw, does STP still exist? I'd like to do some testing on real SMP
> hardware. http://stp.testing.osdl.org/ appears to be dead.
I believe that it has indeed passed on.
I have occasional access to some 128-CPU machines, but they both
currently being used for a week-long test sequence, so I won't have
access to them for some time. Once they free up, I would be happy to
run some short (a few hours) tests on them, given a patch stack starting
from a Linux release (e.g., 2.6.27-rc1). Given such a patch stack, I
can simply point the machine at it. The automated test system doesn't
yet understand git trees. :-/
My hope is that the SGI guys take a look, as they have truly huge
machines.
>>> /*
>>> * It is safe to do non-atomic ops on ->hardirq_context,
>>> diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
>>> index 1658995..811969f 100644
>>> --- a/include/linux/rcuclassic.h
>>> +++ b/include/linux/rcuclassic.h
>>> @@ -28,6 +28,8 @@
>>> * For detailed explanation of Read-Copy Update mechanism see -
>>> * Documentation/RCU
>>> *
>>> + * Rewrite based on a global state machine
>>> + * (C) Manfred Spraul <manfred@...orfullife.com>, 2008
>>> */
>>>
>>> #ifndef __LINUX_RCUCLASSIC_H
>>> @@ -39,88 +41,97 @@
>>> #include <linux/percpu.h>
>>> #include <linux/cpumask.h>
>>> #include <linux/seqlock.h>
>>> +#include <linux/rcucpumask.h>
>>>
>>> +/*
>>> + * global state machine:
>>> + * - each cpu regularly check the global state and compares it with it's
>>> own local state.
>>> + * - if both state do not match, then the cpus do the required work and
>>> afterwards
>>> + * - update their local state
>>> + * - clear their bit in the cpu bitmask.
>>> + * The state machine is protected by the protocol:
>>> + * The state can only change when all cpus have completed the current
>>> stage, thus
>>> + * random changes cannot happen.
>>> + * The only exception is the change from RCU_STATE_DESTROY to
>>> RCU_STATE_DESTROY_AND_COLLECT,
>>> + * but this change doesn't matter, because RCU_STATE_DESTROY is a subset
>>> of
>>> + * RCU_STATE_DESTROY_AND_COLLECT.
>>> + *
>>> + * The state is stored in the rcu_cpumask structure.
>>> + */
>>>
>>
>> Interesting approach! My main concern would be that this might extend
>> grace periods (which has come up with preemptable RCU). Or do you
>> have some clever way of overlapping the required processing for the
>> various states?
>>
> No, no overlapping at all. But it shouldn't be slower than mainline:
> Mainline has two grace periods between call_rcu() and the rcu callback.
> My approach means one call and one grace period.
>
> Your code might be a bit faster, if I understand it correctly, call_rcu()
> reads rdp->batch and includes everything in the next grace period.
It does indeed optimize a few situations. I expect to be able to get a
few more, for example, call_rcu() can probably check to see if the
current grace period is running, though it mean touching the rcu_state
structure.
>> How do you handle the uncertainty as to when a given state begins?
>> Here is an example sequence of events that I would be worried about:
>>
>> o CPU 0 notices the end of a grace period, so updates the state.
>>
> global state now DESTROY_AND_COLLECT.
>> o CPU 1 notices the new grace period while in a quiescent state.
>> It checks into the RCU state machine.
>>
> DESTROY_AND_COLLECT done for cpu 1. Btw, there is no need that there is a
> quiescent state for this operation.
Ah, OK -- having the quiescent states for both phases would seem to
handle it.
>> o CPU 1 starts a long-running RCU read-side critical section.
>>
>> o CPU 2 deletes one of the elements that CPU 1 is referencing,
>> and registers an RCU callback to free it after a grace period.
>>
>>
> >>> ok - here is call_rcu(). element in rcs->new.
>> o CPU 2 notices that a new grace period has commenced.
>>
>>
> CPU 2 notices DESTROY_AND_COLLECT. Moves all elements from rcs->new to
> rcs->old.
>> o The remaining CPUs (other than CPU 1, which already passed
>> through a quiescent state) pass through a quiescent state, ending
>> the grace period. CPU 1 remains in its RCU read-side critical
>> section.
>>
> someone notices that DESTROY_AND_COLLECT is completed, moves global state
> to GRACE.
>> o The RCU grace period ends, permitting CPU 2 to free the element
>> that it removed -- but which CPU 1 is still referencing.
>>
> No - that's impossible. The grace period is started when the global state
> is set to GRACE, all cpus must pass a quiescent state while in GRACE.
> What is still missing is:
> - all cpus must pass a quiescent state.
> - last cpus moves global state to DESTROY
> - cpu 2 notices that the global state is DESTROY. It moves the elements
> from rcs->new to rcd->dead and the softirq will destroy them.
OK, I think. ;-)
I will look your update over later -- the question is "how do the CPUs
know when a grace period has started?" If this question can be answered
with no temporal uncertainty, then we are set.
> Oh - I forgot to list one point in the patch summary:
> I've merged the list of dead pointers for the _bh and the _normal lists.
> rcu_do_batch() operates on a unified list.
Yep. Not yet sure whether this is good or bad in my patch.
>> Jiangshan recently unified this into another stage of
>> queuing, which seems to work very well -- and much more straightforwardly.
>>
> My approach is similar: first all cpus collect the pointers. Then the grace
> period starts. When all cpus have finished, the pointers are destroyed. New
> call_rcu() calls during the grace period are queued.
Yep, that is the general RCU approach for quiescent states. ;-)
>>> +/*
>>> + * FIXME:
>>> + * This is wrong:
>>> + * NMIs are not handled.
>>> + */
>>> #define call_rcu_sched(head, func) call_rcu(head, func)
>>>
>>
>> The approach preemptable RCU uses to interact with dynticks should
>> handle this. You mentioned using atomic operations previously, which
>> might simplify the code (Steve and I were concerned that use of atomic
>> ops in the interrupt path would get an automatic NACK, but it is quite
>> possible that we were being too paranoid).
>>
> I think it was a NACK on sparc, because sparc used a spinlock inside
> atomic_t. I assume it's ok today.
> If it's not ok, then I would have to find another solution. I'll wait for
> complains.
Sounds like a reasonable strategy.
>>> +
>>> +#ifndef __LINUX_RCUCPUMASK_H
>>> +#define __LINUX_RCUCPUMASK_H
>>> +
>>> +#include <linux/spinlock.h>
>>> +#include <linux/cpumask.h>
>>> +
>>> +#define RCUCPUMASK_CPULIMIT 512
>>>
>>
>> People are apparently looking at 4096 CPUs these days, FWIW. I don't
>> see any architectural limit in your code, so just FYI.
>>
>>
> The #define has a bad name: above that limit I would use a hierarchy
> instead of the flag rcu_cumask. The hierarchy is not yet implemented.
>>> +#if (NR_CPUS > RCUCPUMASK_CPULIMIT)
>>> +
>>> +Bla Bla Bla
>>> +
>>>
> Here the miracle occurs: "bla bla bla" is replaced by a rcu_cpumask
> structure with (probably) an array of atomic_t's instead of the simple "int
> cpus_open".
Ah! I was interpreting "Bla Bla Bla" as "#error".
>>> +/*
>>> + * rcu_cpumode:
>>> + * -1:
>>> + * "normal" rcu behavior: the scheduler and the timer interrupt
>>> + * check for grace periods, read side critical sections are permitted
>>> + * everywhere.
>>> + *
>>> + * 0:
>>> + * This cpu is sitting in the idle thread, with disabled hz timer.
>>> + *
>>> + * > 0:
>>> + * The cpu is in an interrupt that interrupted a nohz idle thread.
>>> + */
>>
>> This could be made to work, but the advantage of preemptable RCU's
>> upcounter approach is the ability to count momentarily dropping into
>> dyntick idle mode as a quiescent state -- even if we don't happen to
>> look at that CPU while it is actually residing in dyntick idle mode.
>>
> My code does that same thing: When "0", the cpu is ignored by the state
> machine, the cpu is assumed to be outside any read side critical sections.
> When switching from "1" to "0", the outstanding work for the current state
> is performed.
OK, seems reasonable. I should also put a cpu_quiet() into
rcu_enter_nohz() and friends. Still need to sample state for CPUs that
remain in NO_HZ idle for the entire grace period, but still would help.
> That's for the detailed review!
>
> Attached is an updated patch, NO_HZ and NMI is now implemented.
I will look it over!
Thanx, Paul
> --
> Manfred
> xxx From 1445cbb7b30b4c918ad9efd2997b0dae76ba7ace Mon Sep 17 00:00:00 2001
> xxx From: Manfred Spraul <manfred@...orfullife.com>
> Date: Fri, 22 Aug 2008 14:51:54 +0200
> Subject: [PATCH] kernel/rcustate.c: state machine based rcu implementation.
>
> I've decided to move the state machine based rcu code into
> a separate file, that's simpler to maintain.
> Very few updates are needed outside the new files.
> The code contains a few new ideas for the "classic" rcu code:
>
> Right now, each cpu locally decides what it does, the only
> global thing is the bitmap that keeps track of grace periods.
> What this grace period means is defined by the cpu: it's possible
> that some cpus interpret a grace period as the sign for
> calling the rcu callbacks, other cpus interpret it as the
> sign that they should stop accepting further call_rcu()
> calls and start waiting for the next grace period.
>
> The patch adds a global state, now all cpus do the same thing.
> The system is either collecting pointers for the next grace
> period, or it's waiting for a grace period to complete.
> This helps, because both calls are different:
> - for collecting pointers, any context is acceptable.
> - for the end of the grace period, the call must be from
> outside critical sections.
>
> Each cpu compares it's own state with the global state.
> If they do not match, then it must do something.
>
> Additionally, the patch removes the cpu bitmask:
> Since all cpus must do something and the only thing that
> is tested for is an empty bitmask, the bitmask can be replaced
> with an integer that counts the outstanding cpus.
> (right now, the bitmasks are still there, but just for debugging).
>
> If needed, a slow path could reconstruct the bitmap on the fly.
> {for_each_online_cpu(i) if (rcu_pending(i) {do_something()} }
>
> The code in kernel/rcustate.c also has a unified list for the
> dead structures of call_rcu(), call_rcu_sched() and call_rcu_bh():
> There is no need to treat the outstanding callbacks differently,
> thus one list is sufficient.
>
> The patch is work in progress:
> - The counters could be made hierarchical for better scalability.
> - The counters could be replaced by atomic_t
> - The bitmaps could be removed.
> - The patch doesn't contain the new debug features in rcu classic.
> - The patch doesn't contain a force_quiescent_state() implementation.
> - The Kconfig file is probably incorrect.
>
> I'm interested in test feedback: with qemu & 8 cpus, fedora boots
> into runlevel 3, logging in works.
>
> The patch is against tip/rcu.
> ---
> include/linux/hardirq.h | 27 +-
> include/linux/rcuclassic.h | 2 -
> include/linux/rcucpumask.h | 154 +++++++
> include/linux/rcupdate.h | 19 +-
> include/linux/rcupreempt.h | 14 -
> include/linux/rcustate.h | 199 +++++++++
> init/Kconfig | 12 +-
> kernel/Makefile | 1 +
> kernel/rcuclassic.c | 20 +-
> kernel/rcucpumask.c | 119 ++++++
> kernel/rcupreempt.c | 6 +-
> kernel/rcustate.c | 961 ++++++++++++++++++++++++++++++++++++++++++++
> kernel/softirq.c | 2 +-
> 13 files changed, 1501 insertions(+), 35 deletions(-)
> create mode 100644 include/linux/rcucpumask.h
> create mode 100644 include/linux/rcustate.h
> create mode 100644 kernel/rcucpumask.c
> create mode 100644 kernel/rcustate.c
>
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index 181006c..4c064a3 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -118,13 +118,13 @@ static inline void account_system_vtime(struct task_struct *tsk)
> }
> #endif
>
> -#if defined(CONFIG_PREEMPT_RCU) && defined(CONFIG_NO_HZ)
> -extern void rcu_irq_enter(void);
> -extern void rcu_irq_exit(void);
> +#ifdef CONFIG_NO_HZ
> +extern void rcu_irq_enter(int in_nmi);
> +extern void rcu_irq_exit(int in_nmi);
> #else
> -# define rcu_irq_enter() do { } while (0)
> -# define rcu_irq_exit() do { } while (0)
> -#endif /* CONFIG_PREEMPT_RCU */
> +# define rcu_irq_enter(in_nmi) do { } while (0)
> +# define rcu_irq_exit(in_nmi) do { } while (0)
> +#endif /* CONFIG_NO_HZ */
>
> /*
> * It is safe to do non-atomic ops on ->hardirq_context,
> @@ -132,14 +132,17 @@ extern void rcu_irq_exit(void);
> * always balanced, so the interrupted value of ->hardirq_context
> * will always be restored.
> */
> -#define __irq_enter() \
> +#define ____irq_enter(in_nmi) \
> do { \
> - rcu_irq_enter(); \
> + rcu_irq_enter(in_nmi); \
> account_system_vtime(current); \
> add_preempt_count(HARDIRQ_OFFSET); \
> trace_hardirq_enter(); \
> } while (0)
>
> +#define __irq_enter() ____irq_enter(0)
> +#define __irq_exit() ____irq_exit(0)
> +
> /*
> * Enter irq context (on NO_HZ, update jiffies):
> */
> @@ -148,12 +151,12 @@ extern void irq_enter(void);
> /*
> * Exit irq context without processing softirqs:
> */
> -#define __irq_exit() \
> +#define ____irq_exit(in_nmi) \
> do { \
> trace_hardirq_exit(); \
> account_system_vtime(current); \
> sub_preempt_count(HARDIRQ_OFFSET); \
> - rcu_irq_exit(); \
> + rcu_irq_exit(in_nmi); \
> } while (0)
>
> /*
> @@ -161,7 +164,7 @@ extern void irq_enter(void);
> */
> extern void irq_exit(void);
>
> -#define nmi_enter() do { lockdep_off(); __irq_enter(); } while (0)
> -#define nmi_exit() do { __irq_exit(); lockdep_on(); } while (0)
> +#define nmi_enter() do { lockdep_off(); ____irq_enter(1); } while (0)
> +#define nmi_exit() do { ____irq_exit(1); lockdep_on(); } while (0)
>
> #endif /* LINUX_HARDIRQ_H */
> diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
> index 1658995..fc3047f 100644
> --- a/include/linux/rcuclassic.h
> +++ b/include/linux/rcuclassic.h
> @@ -162,8 +162,6 @@ extern struct lockdep_map rcu_lock_map;
>
> #define __synchronize_sched() synchronize_rcu()
>
> -#define call_rcu_sched(head, func) call_rcu(head, func)
> -
> extern void __rcu_init(void);
> #define rcu_init_sched() do { } while (0)
> extern void rcu_check_callbacks(int cpu, int user);
> diff --git a/include/linux/rcucpumask.h b/include/linux/rcucpumask.h
> new file mode 100644
> index 0000000..0a650dd
> --- /dev/null
> +++ b/include/linux/rcucpumask.h
> @@ -0,0 +1,154 @@
> +/*
> + * cpu mask with integrated locking, intended for rcu
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
> + *
> + * (C) Manfred Spraul <manfred@...orfullife.com>, 2008
> + *
> + */
> +
> +#ifndef __LINUX_RCUCPUMASK_H
> +#define __LINUX_RCUCPUMASK_H
> +
> +#include <linux/spinlock.h>
> +#include <linux/cpumask.h>
> +
> +#define RCUCPUMASK_CPULIMIT 512
> +
> +#if (NR_CPUS > RCUCPUMASK_CPULIMIT)
> +
> +Bla Bla Bla
> +
> +#elif (NR_CPUS > 1)
> +
> +/*
> + * cpu bitmask:
> + * "normal" implementation, single spinlock.
> + */
> +
> +#define RCUCPUMASK_FLAT 1
> +
> +struct rcu_cpumask {
> + spinlock_t lock;
> +
> + /* number of cpus that are tracked by rcu */
> + int cpus_total;
> +
> + /* number of cpus that are still unresolved */
> + int cpus_open;
> +
> + int state ____cacheline_internodealigned_in_smp;
> +
> + /* debug only: two bitmaps to double check the counters */
> + cpumask_t mask_cpu_total;
> + cpumask_t mask_cpu_open;
> +} ____cacheline_internodealigned_in_smp;
> +
> +#define __RCU_CPUMASK_INIT(ptr) { .lock = __SPIN_LOCK_UNLOCKED(&(ptr)->lock) }
> +
> +/**
> + * rcu_cpumask_init(rcm, new_state) - initialize cpu mask with all live cpus.
> + * @rcm: rcu cpumask pointer.
> + * @new_state: new global state of the state machine
> + *
> + * This function sets the cpu bits for all cpus that might read pointers
> + * to rcu protected structures.
> + */
> +extern void rcu_cpumask_init(struct rcu_cpumask *rcm, int newstate, int setupcpus);
> +
> +/**
> + * rcu_cpumask_clear_and_test(rcm, cpu) - remove one cpu from cpumask
> + * @rcm: rcu cpumask pointer.
> + * @cpu: cpu to remove
> + *
> + * This function clears the bit for the given @cpu from the cpu mask.
> + * If no other bits are set, then the function returns 1, otherwise 0.
> + */
> +extern int rcu_cpumask_clear_and_test(struct rcu_cpumask *rcm, int cpu);
> +
> +/**
> + * rcu_cpumask_addcpu(rcm, cpu) - list a cpu as important for rcu
> + * @rcm: rcu cpumask pointer.
> + * @cpu: cpu to remove
> + *
> + * This function adds the given cpu to the list of cpus that might access
> + * rcu related structures.
> + * The function return the current state, i.e. the state for which the cpu
> + * doesn't need to do anything.
> + */
> +extern int rcu_cpumask_addcpu(struct rcu_cpumask *rcm, int cpu);
> +
> +/**
> + * rcu_cpumask_removecpu(rcm, cpu) - remove a cpu from cpu list.
> + * @rcm: rcu cpumask pointer.
> + * @cpu: cpu to remove
> + *
> + * The function removes the given @cpu from the list of rcu related cpus.
> + * A cpu that is not listed must neither call call_rcu() nor access any
> + * rcu protected structures.
> + *
> + * The function returns the state for which the cpu is still listed,
> + * i.e. the cpu must do the work for that state.
> + */
> +extern int rcu_cpumask_removecpu(struct rcu_cpumask *rcm, int cpu);
> +
> +#else /* NR_CPUS == 1 */
> +
> +/*
> + * cpu bitmask: uniprocessor optimized.
> + * - there is just one cpu, it's always online.
> + * - clear_and_test always clears the only bit that could be set,
> + * thus it always returns 1.
> + * Conclusion: No datastorage at all needed.
> + */
> +
> +struct rcu_cpumask {
> + int state;
> +};
> +
> +#define __RCU_CPUMASK_INIT(ptr) { .state = 0 }
> +
> +static inline void rcu_cpumask_init(struct rcu_cpumask *rcm, int newstate, int setupcpus)
> +{
> + rcm->state = newstate;
> +}
> +static inline int rcu_cpumask_clear_and_test(struct rcu_cpumask *rcm, int cpu)
> +{
> + return 1;
> +}
> +static inline int rcu_cpumask_addcpu(struct rcu_cpumask *rcm, int cpu)
> +{
> + return rcm->state;
> +}
> +
> +static inline int rcu_cpumask_removecpu(struct rcu_cpumask *rcm, int cpu)
> +{
> + return rcm->state;
> +}
> +
> +#endif /* NR_CPUS == 1 */
> +
> +/**
> + * rcu_cpumask_getstate(rcm) - retrieve the current state
> + * @rcm: rcu cpumask pointer.
> + *
> + * This function returns the current state from the cpu mask.
> + */
> +static inline int rcu_cpumask_getstate(struct rcu_cpumask *rcm)
> +{
> + return rcm->state;
> +}
> +
> +#endif /* __LINUX_RCUCPUMASK_H */
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index e8b4039..b75035c 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -52,7 +52,9 @@ struct rcu_head {
> void (*func)(struct rcu_head *head);
> };
>
> -#ifdef CONFIG_CLASSIC_RCU
> +#ifdef CONFIG_STATE_RCU
> +#include <linux/rcustate.h>
> +#elif CONFIG_CLASSIC_RCU
> #include <linux/rcuclassic.h>
> #else /* #ifdef CONFIG_CLASSIC_RCU */
> #include <linux/rcupreempt.h>
> @@ -243,6 +245,21 @@ extern void call_rcu(struct rcu_head *head,
> extern void call_rcu_bh(struct rcu_head *head,
> void (*func)(struct rcu_head *head));
>
> +/**
> + * call_rcu_sched - Queue RCU callback for invocation after sched grace period.
> + * @head: structure to be used for queueing the RCU updates.
> + * @func: actual update function to be invoked after the grace period
> + *
> + * The update function will be invoked some time after a full
> + * synchronize_sched()-style grace period elapses, in other words after
> + * all currently executing preempt-disabled sections of code (including
> + * hardirq handlers, NMI handlers, and local_irq_save() blocks) have
> + * completed.
> + */
> +extern void call_rcu_sched(struct rcu_head *head,
> + void (*func)(struct rcu_head *head));
> +
> +
> /* Exported common interfaces */
> extern void synchronize_rcu(void);
> extern void rcu_barrier(void);
> diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h
> index 3e05c09..bef8562 100644
> --- a/include/linux/rcupreempt.h
> +++ b/include/linux/rcupreempt.h
> @@ -65,20 +65,6 @@ static inline void rcu_qsctr_inc(int cpu)
> */
> #define call_rcu_bh call_rcu
>
> -/**
> - * call_rcu_sched - Queue RCU callback for invocation after sched grace period.
> - * @head: structure to be used for queueing the RCU updates.
> - * @func: actual update function to be invoked after the grace period
> - *
> - * The update function will be invoked some time after a full
> - * synchronize_sched()-style grace period elapses, in other words after
> - * all currently executing preempt-disabled sections of code (including
> - * hardirq handlers, NMI handlers, and local_irq_save() blocks) have
> - * completed.
> - */
> -extern void call_rcu_sched(struct rcu_head *head,
> - void (*func)(struct rcu_head *head));
> -
> extern void __rcu_read_lock(void) __acquires(RCU);
> extern void __rcu_read_unlock(void) __releases(RCU);
> extern int rcu_pending(int cpu);
> diff --git a/include/linux/rcustate.h b/include/linux/rcustate.h
> new file mode 100644
> index 0000000..32557d1
> --- /dev/null
> +++ b/include/linux/rcustate.h
> @@ -0,0 +1,199 @@
> +/*
> + * Read-Copy Update mechanism for mutual exclusion (classic version)
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
> + *
> + * Copyright IBM Corporation, 2001
> + *
> + * Author: Dipankar Sarma <dipankar@...ibm.com>
> + *
> + * Based on the original work by Paul McKenney <paulmck@...ibm.com>
> + * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
> + * Papers:
> + * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
> + * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
> + *
> + * For detailed explanation of Read-Copy Update mechanism see -
> + * Documentation/RCU
> + *
> + * Rewrite based on a global state machine
> + * (C) Manfred Spraul <manfred@...orfullife.com>, 2008
> + */
> +
> +#ifndef __LINUX_RCUCLASSIC_H
> +#define __LINUX_RCUCLASSIC_H
> +
> +#include <linux/cache.h>
> +#include <linux/spinlock.h>
> +#include <linux/threads.h>
> +#include <linux/percpu.h>
> +#include <linux/cpumask.h>
> +#include <linux/seqlock.h>
> +#include <linux/rcucpumask.h>
> +
> +/*
> + * global state machine:
> + * - each cpu regularly check the global state and compares it with it's own local state.
> + * - if both state do not match, then the cpus do the required work and afterwards
> + * - update their local state
> + * - clear their bit in the cpu bitmask.
> + * The state machine is protected by the protocol:
> + * The state can only change when all cpus have completed the current stage, thus
> + * random changes cannot happen.
> + * The only exception is the change from RCU_STATE_DESTROY to RCU_STATE_DESTROY_AND_COLLECT,
> + * but this change doesn't matter, because RCU_STATE_DESTROY is a subset of
> + * RCU_STATE_DESTROY_AND_COLLECT.
> + *
> + * The state is stored in the rcu_cpumask structure.
> + */
> +
> +/* RCU_STATE_DESTROY:
> + * call callbacks that were registered by call_rcu for the objects in rcu_cpu_state.old
> + */
> +#define RCU_STATE_DESTROY 1
> +/* RCU_STATE_DESTROY_AND_COLLECT:
> + * - call callbacks that were registered by call_rcu for the objects in rcu_cpu_state.old
> + * - move the objects from rcu_cpu_state.new to rcu_cpu_state.new
> + */
> +#define RCU_STATE_DESTROY_AND_COLLECT 2
> +/* RCU_STATE_GRACE
> + * - wait for a quiescent state
> + */
> +#define RCU_STATE_GRACE 3
> +
> +struct rcu_global_state {
> + seqlock_t lock;
> + int start_immediately;
> + long completed;
> + struct rcu_cpumask cpus;
> +} ____cacheline_internodealigned_in_smp;
> +
> +struct rcu_cpu_state {
> + int state;
> +
> + int mode;
> + int count;
> + /* new objects, directly from call_rcu().
> + * The list are length-based, not NULL-terminated.
> + */
> + struct rcu_head *new; /* new objects */
> + struct rcu_head **newtail;
> + long newqlen; /* # of queued callbacks */
> +
> + unsigned long timeout;
> +
> + /* objects that are in rcu grace processing. The actual
> + * state depends on rcu_cpumask_getstate(&rgs->cpus);
> + */
> + struct rcu_head *old;
> + struct rcu_head **oldtail;
> + long oldqlen;
> +
> + /*
> + * quiescent state looking:
> + * When the cpu sees RCU_STATE_DESTROY_AND_COLLECT, it clears looking.
> + * When the cpu sees RCU_STATE_GRACE, it sets looking and clears
> + * quiet.
> + * If looking and quiet are both set, then there was a grace period,
> + * even if the state machine is called from non-idle context.
> + */
> + int quiet;
> + int looking;
> +};
> +
> +/* Note: only one structure for _bh and _normal. */
> +struct rcu_cpu_dead {
> + /*
> + * objects that are scheduled for immediate call of
> + * ->func().
> + */
> + struct rcu_head *dead;
> + struct rcu_head **deadtail;
> + long deadqlen;
> +
> + long batchcount;
> +};
> +
> +DECLARE_PER_CPU(struct rcu_cpu_state, rcu_cpudata_normal);
> +DECLARE_PER_CPU(struct rcu_cpu_state, rcu_cpudata_bh);
> +DECLARE_PER_CPU(struct rcu_cpu_dead, rcu_cpudata_dead);
> +
> +extern long rcu_batches_completed(void);
> +extern long rcu_batches_completed_bh(void);
> +
> +extern int rcu_pending(int cpu);
> +extern int rcu_needs_cpu(int cpu);
> +
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +extern struct lockdep_map rcu_lock_map;
> +# define rcu_read_acquire() \
> + lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_)
> +# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
> +#else
> +# define rcu_read_acquire() do { } while (0)
> +# define rcu_read_release() do { } while (0)
> +#endif
> +
> +#define __rcu_read_lock() \
> + do { \
> + preempt_disable(); \
> + __acquire(RCU); \
> + rcu_read_acquire(); \
> + } while (0)
> +#define __rcu_read_unlock() \
> + do { \
> + rcu_read_release(); \
> + __release(RCU); \
> + preempt_enable(); \
> + } while (0)
> +#define __rcu_read_lock_bh() \
> + do { \
> + local_bh_disable(); \
> + __acquire(RCU_BH); \
> + rcu_read_acquire(); \
> + } while (0)
> +#define __rcu_read_unlock_bh() \
> + do { \
> + rcu_read_release(); \
> + __release(RCU_BH); \
> + local_bh_enable(); \
> + } while (0)
> +
> +extern void __rcu_init(void);
> +#define rcu_init_sched() do { } while (0)
> +
> +extern void __synchronize_sched(void);
> +extern void rcu_check_callbacks(int cpu, int user);
> +
> +#ifdef CONFIG_NO_HZ
> +extern void rcu_enter_nohz(void);
> +extern void rcu_exit_nohz(void);
> +#else /* CONFIG_NO_HZ */
> +#define rcu_enter_nohz() do { } while (0)
> +#define rcu_exit_nohz() do { } while (0)
> +#endif /* CONFIG_NO_HZ */
> +
> +static inline void rcu_qsctr_inc(int cpu)
> +{
> + per_cpu(rcu_cpudata_normal, cpu).quiet = 1;
> + per_cpu(rcu_cpudata_bh, cpu).quiet = 1;
> +}
> +
> +static inline void rcu_bh_qsctr_inc(int cpu)
> +{
> + per_cpu(rcu_cpudata_bh, cpu).quiet = 1;
> +}
> +
> +#endif /* __LINUX_RCUCLASSIC_H */
> diff --git a/init/Kconfig b/init/Kconfig
> index b678803..faa7bba 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -914,10 +914,20 @@ source "block/Kconfig"
> config PREEMPT_NOTIFIERS
> bool
>
> +config STATE_RCU
> + bool
> + default y
> + help
> + This option selects a state machine based RCU implementation.
> + It's a replacement for the "classic" rcu implementation that
> + aims simpler code and better scalability.
> + If unsure, say N.
> +
> config CLASSIC_RCU
> - def_bool !PREEMPT_RCU
> + def_bool !PREEMPT_RCU && !STATE_RCU
> help
> This option selects the classic RCU implementation that is
> designed for best read-side performance on non-realtime
> systems. Classic RCU is the default. Note that the
> PREEMPT_RCU symbol is used to select/deselect this option.
> +
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 4e1d7df..6bc9503 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -74,6 +74,7 @@ obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
> obj-$(CONFIG_SECCOMP) += seccomp.o
> obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
> obj-$(CONFIG_CLASSIC_RCU) += rcuclassic.o
> +obj-$(CONFIG_STATE_RCU) += rcustate.o rcucpumask.o
> obj-$(CONFIG_PREEMPT_RCU) += rcupreempt.o
> ifeq ($(CONFIG_PREEMPT_RCU),y)
> obj-$(CONFIG_RCU_TRACE) += rcupreempt_trace.o
> diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
> index 01e761a..39fde99 100644
> --- a/kernel/rcuclassic.c
> +++ b/kernel/rcuclassic.c
> @@ -215,6 +215,13 @@ void call_rcu_bh(struct rcu_head *head,
> }
> EXPORT_SYMBOL_GPL(call_rcu_bh);
>
> +void call_rcu_sched(struct rcu_head *head,
> + void (*func)(struct rcu_head *rcu))
> +{
> + call_rcu(head, func);
> +}
> +EXPORT_SYMBOL_GPL(call_rcu_sched);
> +
> /*
> * Return the number of RCU batches processed thus far. Useful
> * for debug and statistics.
> @@ -710,7 +717,7 @@ void rcu_check_callbacks(int cpu, int user)
> static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
> struct rcu_data *rdp)
> {
> - long flags;
> + unsigned long flags;
>
> spin_lock_irqsave(&rcp->lock, flags);
> memset(rdp, 0, sizeof(*rdp));
> @@ -757,6 +764,17 @@ static struct notifier_block __cpuinitdata rcu_nb = {
> .notifier_call = rcu_cpu_notify,
> };
>
> +#ifdef CONFIG_NO_HZ
> +
> +void rcu_irq_enter(int in_nmi)
> +{
> +}
> +
> +void rcu_irq_exit(int in_nmi)
> +{
> +}
> +#endif
> +
> /*
> * Initializes rcu mechanism. Assumed to be called early.
> * That is before local timer(SMP) or jiffie timer (uniproc) is setup.
> diff --git a/kernel/rcucpumask.c b/kernel/rcucpumask.c
> new file mode 100644
> index 0000000..85ceb1e
> --- /dev/null
> +++ b/kernel/rcucpumask.c
> @@ -0,0 +1,119 @@
> +/*
> + * Scalable cpu mask for rcu.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
> + *
> + * (C) Manfred Spraul <manfred@...orfullife.com>, 2008
> + *
> + */
> +#include <linux/rcucpumask.h>
> +#include <linux/bug.h>
> +
> +#ifdef RCUCPUMASK_FLAT
> +
> +void rcu_cpumask_init(struct rcu_cpumask *rcm, int newstate, int setupcpus)
> +{
> + BUG_ON(!irqs_disabled());
> +
> + spin_lock(&rcm->lock);
> + rcm->state = newstate;
> +
> + if (setupcpus) {
> + rcm->cpus_open = rcm->cpus_total;
> +
> + bitmap_copy(cpus_addr(rcm->mask_cpu_open), cpus_addr(rcm->mask_cpu_total), NR_CPUS);
> + } else {
> + rcm->cpus_open = 0;
> + cpus_clear(rcm->mask_cpu_open);
> + }
> + spin_unlock(&rcm->lock);
> +}
> +
> +int rcu_cpumask_clear_and_test(struct rcu_cpumask *rcm, int cpu)
> +{
> + int ret;
> +
> + BUG_ON(!irqs_disabled());
> +
> + spin_lock(&rcm->lock);
> +
> + BUG_ON(!cpu_isset(cpu, rcm->mask_cpu_open));
> + cpu_clear(cpu, rcm->mask_cpu_open);
> +
> + rcm->cpus_open--;
> +if (rcm->cpus_open < 0) {
> + printk(KERN_ERR" rcm %p cpu %d state %d.\n", rcm, cpu, rcm->state);
> +for(;;);
> +}
> + ret = rcm->cpus_open;
> + if (ret == 0) {
> +if (!cpus_empty(rcm->mask_cpu_open)) {
> + printk(KERN_ERR" rcm %p cpu %d state %d.\n", rcm, cpu, rcm->state);
> +for(;;);
> +}
> + }
> +
> + spin_unlock(&rcm->lock);
> +
> + return !ret;
> +}
> +
> +int rcu_cpumask_addcpu(struct rcu_cpumask *rcm, int cpu)
> +{
> + int ret;
> + unsigned long flags;
> +
> + /*
> + * This function is called both during early bootup (irqs disabled)
> + * and during "normal" CPU_UP notifiers (irqs enabled).
> + */
> + spin_lock_irqsave(&rcm->lock, flags);
> +
> + BUG_ON(cpu_isset(cpu, rcm->mask_cpu_total));
> + cpu_set(cpu, rcm->mask_cpu_total);
> +
> + rcm->cpus_total++;
> + ret = rcm->state;
> +
> + spin_unlock_irqrestore(&rcm->lock, flags);
> +
> + return ret;
> +}
> +
> +int rcu_cpumask_removecpu(struct rcu_cpumask *rcm, int cpu)
> +{
> + int ret;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&rcm->lock, flags);
> +
> + BUG_ON(!cpu_isset(cpu, rcm->mask_cpu_total));
> + cpu_clear(cpu, rcm->mask_cpu_total);
> +
> + rcm->cpus_total--;
> + ret = rcm->state;
> +
> + spin_unlock_irqrestore(&rcm->lock, flags);
> +
> + return ret;
> +}
> +
> +#endif /* RCUCPUMASK_FLAT */
> +
> +#ifdef RCUCPUMASK_HIERARCHICAL
> +
> +bla
> +
> +#endif /* RCUCPUMASK_HIERARCHICAL */
> diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
> index ca4bbbe..ab18347 100644
> --- a/kernel/rcupreempt.c
> +++ b/kernel/rcupreempt.c
> @@ -434,13 +434,13 @@ DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched) = {
> static DEFINE_PER_CPU(int, rcu_update_flag);
>
> /**
> - * rcu_irq_enter - Called from Hard irq handlers and NMI/SMI.
> + * __rcu_irq_enter - Called from Hard irq handlers and NMI/SMI.
> *
> * If the CPU was idle with dynamic ticks active, this updates the
> * rcu_dyntick_sched.dynticks to let the RCU handling know that the
> * CPU is active.
> */
> -void rcu_irq_enter(void)
> +void __rcu_irq_enter(int in_nmi)
> {
> int cpu = smp_processor_id();
> struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
> @@ -510,7 +510,7 @@ void rcu_irq_enter(void)
> * rcu_dyntick_sched.dynticks to put let the RCU handling be
> * aware that the CPU is going back to idle with no ticks.
> */
> -void rcu_irq_exit(void)
> +void __rcu_irq_exit(int in_nmi)
> {
> int cpu = smp_processor_id();
> struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
> diff --git a/kernel/rcustate.c b/kernel/rcustate.c
> new file mode 100644
> index 0000000..76ee1fe
> --- /dev/null
> +++ b/kernel/rcustate.c
> @@ -0,0 +1,961 @@
> +/*
> + * Read-Copy Update mechanism for mutual exclusion
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
> + *
> + * Copyright IBM Corporation, 2001
> + *
> + * Authors: Dipankar Sarma <dipankar@...ibm.com>
> + * Manfred Spraul <manfred@...orfullife.com>
> + *
> + * Based on the original work by Paul McKenney <paulmck@...ibm.com>
> + * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
> + * Papers:
> + * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
> + * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
> + *
> + * For detailed explanation of Read-Copy Update mechanism see -
> + * Documentation/RCU
> + *
> + * Rewrite based on a global state machine
> + * (C) Manfred Spraul <manfred@...orfullife.com>, 2008
> + *
> + */
> +#include <linux/types.h>
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/spinlock.h>
> +#include <linux/smp.h>
> +#include <linux/rcupdate.h>
> +#include <linux/interrupt.h>
> +#include <linux/sched.h>
> +#include <asm/atomic.h>
> +#include <linux/bitops.h>
> +#include <linux/module.h>
> +#include <linux/completion.h>
> +#include <linux/moduleparam.h>
> +#include <linux/percpu.h>
> +#include <linux/notifier.h>
> +#include <linux/cpu.h>
> +#include <linux/mutex.h>
> +#include <linux/time.h>
> +
> +
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +static struct lock_class_key rcu_lock_key;
> +struct lockdep_map rcu_lock_map =
> + STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
> +EXPORT_SYMBOL_GPL(rcu_lock_map);
> +#endif
> +
> +/* Definition for rcupdate control block. */
> +static struct rcu_global_state rcu_global_state_normal = {
> + .lock = __SEQLOCK_UNLOCKED(&rcu_global_state_normal.lock),
> + .start_immediately = 0,
> + .cpus = __RCU_CPUMASK_INIT(&rcu_global_state_normal.cpus)
> +};
> +
> +static struct rcu_global_state rcu_global_state_bh = {
> + .lock = __SEQLOCK_UNLOCKED(&rcu_global_state_bh.lock),
> + .start_immediately = 0,
> + .cpus = __RCU_CPUMASK_INIT(&rcu_global_state_bh.cpus)
> +};
> +
> +DEFINE_PER_CPU(struct rcu_cpu_state, rcu_cpudata_normal) = { 0L };
> +DEFINE_PER_CPU(struct rcu_cpu_state, rcu_cpudata_bh) = { 0L };
> +DEFINE_PER_CPU(struct rcu_cpu_dead, rcu_cpudata_dead) = { 0L };
> +
> +#ifdef CONFIG_NO_HZ
> +/*
> + * NMI Handling:
> + * NMIs on nohz cpus must be handled seperately:
> + * nohz cpus that are outside interrupt are ignored for rcu
> + * grace period checking. For normal interrupt, the cpus
> + * are added back on the fly.
> + * This is impossible for NMIs, NMIs can't take spinlocks.
> + * Therefore a different approach is taken:
> + * On NMI entry, a counter is increased and on exit decreased
> + * again.
> + * call_rcu_sched() polls all cpus and checks that this count is 0.
> + *
> + * Since there is no spinlock(), memory barriers are needed.
> + */
> +static atomic_t rcu_nmi_counter = ATOMIC_INIT(0);
> +
> +DEFINE_PER_CPU(int , rcu_nmi_counter_percpu) = { 0L };
> +
> +#endif
> +
> +
> +/*
> + * rcu_cpumode:
> + * -1:
> + * "normal" rcu behavior: the scheduler and the timer interrupt
> + * check for grace periods, read side critical sections are permitted
> + * everywhere.
> + *
> + * 0:
> + * This cpu is sitting in the idle thread, with disabled hz timer.
> + *
> + * > 0:
> + * The cpu is in an interrupt that interrupted a nohz idle thread.
> + */
> +
> +#define RCU_CPUMODE_INVALID -2
> +#define RCU_CPUMODE_DELAYED -1
> +DEFINE_PER_CPU(int, rcu_cpumode) = { 0L };
> +
> +int qlowmark = 100;
> +
> +long rcu_batches_completed(void)
> +{
> + return rcu_global_state_normal.completed;
> +}
> +
> +long rcu_batches_completed_bh(void)
> +{
> + return rcu_global_state_normal.completed;
> +}
> +
> +/**
> + * rcu_state_startcycle - start the next rcu cycle
> + * @rgs: global rcu state
> + *
> + * The function starts the next rcu cycle, either immediately or
> + * by setting rgs->start_immediately.
> + */
> +static void rcu_state_startcycle(struct rcu_global_state *rgs)
> +{
> + unsigned seq;
> + int do_real_start;
> +
> + BUG_ON(!irqs_disabled());
> + do {
> + seq = read_seqbegin(&rgs->lock);
> + if (rgs->start_immediately == 0) {
> + do_real_start = 1;
> + } else {
> + do_real_start = 0;
> + BUG_ON(rcu_cpumask_getstate(&rgs->cpus) == RCU_STATE_DESTROY);
> + }
> + } while (read_seqretry(&rgs->lock, seq));
> +
> + if (do_real_start) {
> + write_seqlock(&rgs->lock);
> + switch(rcu_cpumask_getstate(&rgs->cpus)) {
> + case RCU_STATE_DESTROY_AND_COLLECT:
> + case RCU_STATE_GRACE:
> + rgs->start_immediately = 1;
> + break;
> + case RCU_STATE_DESTROY:
> + rcu_cpumask_init(&rgs->cpus, RCU_STATE_DESTROY_AND_COLLECT, 1);
> + BUG_ON(rgs->start_immediately);
> + break;
> + default:
> + BUG();
> + }
> + write_sequnlock(&rgs->lock);
> + }
> +}
> +
> +/*
> + * Delay that can occur for synchronize_rcu() callers
> + */
> +#define RCU_MAX_DELAY (HZ/30+1)
> +
> +static void rcu_checkqlen(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs, int inc)
> +{
> + BUG_ON(!irqs_disabled());
> + if (unlikely(rcs->newqlen == 0)) {
> + rcs->timeout = jiffies + RCU_MAX_DELAY;
> + }
> + if ((rcs->newqlen < qlowmark) && (rcs->newqlen+inc >= qlowmark))
> + rcu_state_startcycle(rgs);
> +
> + rcs->newqlen += inc;
> +
> + /*
> + * This is not really a bug, it might happen when interrupt calls
> + * call_rcu() while the cpu is in nohz mode. see rcu_irq_exit
> + */
> + WARN_ON( (rcs->newqlen >= qlowmark) && (rcu_cpumask_getstate(&rgs->cpus) == RCU_STATE_DESTROY));
> +}
> +
> +
> +static void __call_rcu(struct rcu_head *head, struct rcu_global_state *rgs,
> + struct rcu_cpu_state *rcs)
> +{
> + if (rcs->new == NULL) {
> + rcs->new = head;
> + } else {
> + (*rcs->newtail) = head;
> + }
> + rcs->newtail = &head->next;
> +
> + rcu_checkqlen(rgs, rcs, 1);
> +}
> +
> +void call_rcu_sched(struct rcu_head *head,
> + void (*func)(struct rcu_head *rcu))
> +{
> +#if CONFIG_NO_HZ
> + /*
> + * NMI interrupts are not included in rgs->cpus.
> + * Thus we must wait synchroneously until no NMI
> + * is running.
> + */
> + /*
> + * make all rcu_assign statements visible to
> + * all cpus.
> + */
> + smp_mb();
> +
> + /* quick check: no nmi at all? */
> + if (unlikely(atomic_read(&rcu_nmi_counter) > 0)) {
> + int cpu;
> +
> + /* slow check: check each cpu individually */
> + for_each_online_cpu(cpu) {
> +
> + /* loop while this cpu is in a nmi */
> + while (per_cpu(rcu_nmi_counter_percpu, cpu) > 0) {
> + cpu_relax();
> + }
> +
> + /* quick check: if noone is in an nmi, then we can exit
> + * immediately, without checking the remaining cpus.
> + */
> + if (atomic_read(&rcu_nmi_counter) == 0)
> + break;
> +
> + cpu_relax();
> + }
> + }
> +#endif
> + call_rcu(head, func);
> +}
> +
> +EXPORT_SYMBOL_GPL(call_rcu_sched);
> +
> +/*
> + * Wait until all currently running preempt_disable() code segments
> + * (including hardware-irq-disable segments) complete. Note that
> + * in -rt this does -not- necessarily result in all currently executing
> + * interrupt -handlers- having completed.
> + */
> +synchronize_rcu_xxx(__synchronize_sched, call_rcu_sched)
> +EXPORT_SYMBOL_GPL(__synchronize_sched);
> +
> +
> +void call_rcu(struct rcu_head *head,
> + void (*func)(struct rcu_head *rcu))
> +{
> + unsigned long flags;
> +
> + head->func = func;
> + local_irq_save(flags);
> + __call_rcu(head, &rcu_global_state_normal, &__get_cpu_var(rcu_cpudata_normal));
> + local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(call_rcu);
> +
> +void call_rcu_bh(struct rcu_head *head,
> + void (*func)(struct rcu_head *rcu))
> +{
> + unsigned long flags;
> +
> + head->func = func;
> + local_irq_save(flags);
> + __call_rcu(head, &rcu_global_state_bh, &__get_cpu_var(rcu_cpudata_bh));
> + local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(call_rcu_bh);
> +
> +#define RCU_BATCH_MIN 100
> +#define RCU_BATCH_INCFACTOR 2
> +#define RCU_BATCH_DECFACTOR 4
> +
> +static void rcu_move_and_raise(struct rcu_cpu_state *rcs, int do_raise)
> +{
> + struct rcu_cpu_dead *rcd = &get_cpu_var(rcu_cpudata_dead);
> +
> + BUG_ON(!irqs_disabled());
> +
> + /* update batch limit:
> + * - if there are still old entries when new entries are added:
> + * double the batch count.
> + * - if there are no old entries: reduce it by 25%, but never below 100.
> + */
> + if (rcd->deadqlen)
> + rcd->batchcount = rcd->batchcount*RCU_BATCH_INCFACTOR;
> + else
> + rcd->batchcount = rcd->batchcount-rcd->batchcount/RCU_BATCH_DECFACTOR;
> + if (rcd->batchcount < RCU_BATCH_MIN)
> + rcd->batchcount = RCU_BATCH_MIN;
> +
> + if (rcs->old != NULL) {
> + if (rcd->dead == NULL) {
> + rcd->dead = rcs->old;
> + } else {
> + (*rcd->deadtail) = rcs->old;
> + }
> + rcd->deadtail = rcs->oldtail;
> + rcd->deadqlen += rcs->oldqlen;
> + }
> +
> + rcs->old = NULL;
> + rcs->oldtail = NULL;
> + rcs->oldqlen = 0;
> +
> + if (do_raise)
> + raise_softirq(RCU_SOFTIRQ);
> +
> + put_cpu_var(rcu_cpudata_dead);
> +}
> +
> +static void __rcu_state_machine(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs,
> + int global_state, int is_quiet, int do_raise, int cpu)
> +{
> + int inc_state;
> + unsigned long flags;
> +
> + /*
> + * Theoretically, this code should run under read_seqbegin().
> + * But: important chages (i.e. from COLLECT to GRACE,
> + * from GRACE to DESTROY) only happen when all cpus have completed
> + * their work. If rcu_cpumask_getstate(&rgs->cpus) != rcs->state, then we haven't completed
> + * our work yet. Thus such a change cannot happen.
> + * The only change that might happen is a change from RCU_STATE_DESTROY
> + * to RCU_STATE_DESTROY_AND_COLLECT. We'll notice that in the next
> + * round.
> + * no need for an mb() either - it simply doesn't matter.
> + * Actually: when rcu_state_startcycle() is called, then it's guaranteed
> + * that global_state and rcu_cpumask_getstate(&rgs->cpus) do not match...
> + */
> + local_irq_save(flags);
> + if (global_state == RCU_STATE_DESTROY && rcs->newqlen > 0 &&
> + time_after(jiffies, rcs->timeout) && do_raise) {
> + rcu_state_startcycle(rgs);
> + }
> +
> + inc_state = 0;
> + if (global_state != rcs->state) {
> + switch(global_state) {
> + case RCU_STATE_DESTROY:
> + rcs->state = RCU_STATE_DESTROY;
> + rcu_move_and_raise(rcs, do_raise);
> + break;
> + case RCU_STATE_DESTROY_AND_COLLECT:
> + rcs->state = RCU_STATE_DESTROY_AND_COLLECT;
> + rcu_move_and_raise(rcs, do_raise);
> + rcs->old = rcs->new;
> + rcs->oldtail = rcs->newtail;
> + rcs->oldqlen = rcs->newqlen;
> + rcs->new = NULL;
> + rcs->newtail = NULL;
> + rcs->newqlen = 0;
> + rcs->looking = 0;
> + if (rcu_cpumask_clear_and_test(&rgs->cpus, cpu))
> + inc_state = 1;
> + break;
> + case RCU_STATE_GRACE:
> + if (is_quiet || (rcs->quiet && rcs->looking)) {
> + rcs->state = RCU_STATE_GRACE;
> + if (rcu_cpumask_clear_and_test(&rgs->cpus, cpu))
> + inc_state = 1;
> + }
> + rcs->quiet = 0;
> + rcs->looking = 1;
> + break;
> + default:
> + BUG();
> + }
> + }
> +
> + if (unlikely(inc_state)) {
> + local_irq_save(flags);
> + write_seqlock(&rgs->lock);
> +
> + BUG_ON(rcu_cpumask_getstate(&rgs->cpus) != rcs->state);
> + BUG_ON(global_state != rcu_cpumask_getstate(&rgs->cpus));
> + /*
> + * advance the state machine:
> + * - from COLLECT to GRACE
> + * - from GRACE to DESTROY/COLLECT
> + */
> + switch(rcu_cpumask_getstate(&rgs->cpus)) {
> + case RCU_STATE_DESTROY_AND_COLLECT:
> + rcu_cpumask_init(&rgs->cpus, RCU_STATE_GRACE, 1);
> + break;
> + case RCU_STATE_GRACE:
> + rgs->completed++;
> + if (rgs->start_immediately) {
> + rcu_cpumask_init(&rgs->cpus, RCU_STATE_DESTROY_AND_COLLECT, 1);
> + } else {
> + rcu_cpumask_init(&rgs->cpus, RCU_STATE_DESTROY, 0);
> + }
> + rgs->start_immediately = 0;
> + break;
> + default:
> + BUG();
> + }
> + write_sequnlock(&rgs->lock);
> + local_irq_restore(flags);
> + }
> +}
> +
> +static void rcu_state_machine(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs, int is_quiet, int cpu)
> +{
> + int global_state = rcu_cpumask_getstate(&rgs->cpus);
> +
> + /* gcc should not optimize away the local variable global_state... */
> + barrier();
> + __rcu_state_machine(rgs, rcs, global_state, is_quiet, 1, cpu);
> +}
> +
> +#if defined(CONFIG_HOTPLUG_CPU) || defined (CONFIG_NO_HZ)
> +
> +static void __rcu_remove_cpu(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs, int cpu)
> +{
> + int global_state;
> + unsigned seq;
> +
> + BUG_ON(!irqs_disabled());
> + /* task 1:
> + * Do the work that the cpu is still supposed to do.
> + * We rely on the lock inside the rcu_cpumask, that guarantees that
> + * we neither do too much nor too little.
> + * But do not raise the softirq, the caller is responsible handling
> + * the entries stil in the queues.
> + */
> + global_state = rcu_cpumask_removecpu(&rgs->cpus, cpu);
> +
> + /*
> + * ensure that we are not in the middle of updating
> + * rcu_cpumask_getstate(&rgs->cpus): otherwise __rcu_state_machine()
> + * would return with "nothing to do", although
> + * the cpu must do something.
> + */
> + do {
> + seq = read_seqbegin(&rgs->lock);
> + } while (read_seqretry(&rgs->lock, seq));
> +
> + __rcu_state_machine(rgs, rcs, global_state, 1, 0, cpu);
> +}
> +
> +#endif
> +
> +#ifdef CONFIG_HOTPLUG_CPU
> +/**
> + * rcu_bulk_add - bulk add new rcu objects.
> + * @rgs: global rcu state
> + * @rcs: cpu state
> + * @h: linked list of rcu objects.
> + *
> + * Must be called with enabled local interrupts
> + */
> +static void rcu_bulk_add(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs, struct rcu_head *h, struct rcu_head **htail, int len)
> +{
> +
> + BUG_ON(irqs_disabled());
> +
> + if (len > 0) {
> + local_irq_disable();
> + if (rcs->new == NULL) {
> + rcs->new = h;
> + } else {
> + (*rcs->newtail) = h;
> + }
> + rcs->newtail = htail;
> +
> + rcu_checkqlen(rgs, rcs, len);
> + local_irq_enable();
> + }
> +}
> +
> +
> +static void __rcu_offline_cpu(struct rcu_global_state *rgs, struct rcu_cpu_state *this_rcs,
> + struct rcu_cpu_state *other_rcs, int cpu)
> +{
> + /*
> + * task 1: Do the work that the other cpu is still supposed to do.
> + */
> + __rcu_remove_cpu(rgs, other_rcs, cpu);
> + per_cpu(rcu_cpumode, cpu) = RCU_CPUMODE_INVALID;
> +
> + /* task 2: move all entries from the new cpu into the lists of the current cpu.
> + * locking: The other cpu is dead, thus no locks are required.
> + * Thus it's more or less a bulk call_rcu().
> + * For the sake of simplicity, all objects are treated as "new", even the objects
> + * that are already in old.
> + */
> + rcu_bulk_add(rgs, this_rcs, other_rcs->new, other_rcs->newtail, other_rcs->newqlen);
> + rcu_bulk_add(rgs, this_rcs, other_rcs->old, other_rcs->oldtail, other_rcs->oldqlen);
> +}
> +
> +static void rcu_offline_cpu(int cpu)
> +{
> + struct rcu_cpu_state *this_rcs_normal = &get_cpu_var(rcu_cpudata_normal);
> + struct rcu_cpu_state *this_rcs_bh = &get_cpu_var(rcu_cpudata_bh);
> + struct rcu_cpu_dead *this_rcd, *other_rcd;
> +
> + BUG_ON(irqs_disabled());
> +
> + /* step 1: move new & old lists, clear cpu bitmask */
> + __rcu_offline_cpu(&rcu_global_state_normal, this_rcs_normal,
> + &per_cpu(rcu_cpudata_normal, cpu), cpu);
> + __rcu_offline_cpu(&rcu_global_state_bh, this_rcs_bh,
> + &per_cpu(rcu_cpudata_bh, cpu), cpu);
> + put_cpu_var(rcu_cpudata_normal);
> + put_cpu_var(rcu_cpudata_bh);
> +
> + /* step 2: move dead list */
> + this_rcd = &get_cpu_var(rcu_cpudata_dead);
> + other_rcd = &per_cpu(rcu_cpudata_dead, cpu);
> +
> + if (other_rcd->dead != NULL) {
> + local_irq_disable();
> + if (this_rcd->dead == NULL) {
> + this_rcd->dead = other_rcd->dead;
> + } else {
> + (*this_rcd->deadtail) = other_rcd->dead;
> + }
> + this_rcd->deadtail = other_rcd->deadtail;
> + this_rcd->deadqlen += other_rcd->deadqlen;
> + local_irq_enable();
> + }
> +
> + put_cpu_var(rcu_cpudata_dead);
> +
> + BUG_ON(rcu_needs_cpu(cpu));
> +}
> +
> +#else
> +
> +static void rcu_offline_cpu(int cpu)
> +{
> +}
> +
> +#endif
> +
> +static int __rcu_pending(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs)
> +{
> + /*
> + * This cpu must do something for the state machine.
> + */
> + if (rcu_cpumask_getstate(&rgs->cpus) != rcs->state)
> + return 1;
> + /*
> + * The state machine is stopped and the current
> + * cpu has outstanding rcu callbacks
> + */
> + if (rcs->state == RCU_STATE_DESTROY && rcs->newqlen)
> + return 1;
> +
> + return 0;
> +}
> +
> +/**
> + * void rcu_pending(int cpu) - check for pending rcu related work.
> + * @cpu: cpu to check.
> + *
> + * Check to see if there is any immediate RCU-related work to be done
> + * by the current CPU, returning 1 if so. This function is part of the
> + * RCU implementation; it is -not- an exported member of the RCU API.
> + *
> + * This function is inherently racy: If it returns 1, then there is something
> + * to do. If it return 0, then there was nothing to do. It's possible that
> + * by the time rcu_pending returns, there is now something to do.
> + *
> + */
> +int rcu_pending(int cpu)
> +{
> + return __rcu_pending(&rcu_global_state_normal, &per_cpu(rcu_cpudata_normal, cpu)) ||
> + __rcu_pending(&rcu_global_state_bh, &per_cpu(rcu_cpudata_bh, cpu));
> +}
> +
> +static int __rcu_needs_cpu(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs)
> +{
> + if (rcs->new)
> + return 1;
> + if (rcs->old)
> + return 1;
> + return 0;
> +}
> +
> +/**
> + * void rcu_needs_cpu(cpu) - check for outstanding rcu work.
> + * @cpu: cpu to check.
> + *
> + * Check to see if any future RCU-related work will need to be done
> + * by @cpu, even if none need be done immediately, returning
> + * 1 if so. This function is part of the RCU implementation; it is -not-
> + * an exported member of the RCU API.
> + *
> + * Locking only works properly if the function is called for the current
> + * cpu and with disabled local interupts. It's a prerequisite for
> + * rcu_nohz_enter() that rcu_needs_cpu() return 0. Local interupts must not
> + * be enabled in between, otherwise a softirq could call call_rcu().
> + *
> + * Note: rcu_needs_cpu() can be 0 (cpu not needed) even though rcu_pending()
> + * returns 1. This means that the outstanding work can be completed by either
> + * the CPU_DEAD callback or rcu_enter_nohz().
> + */
> +int rcu_needs_cpu(int cpu)
> +{
> + int ret;
> +
> + WARN_ON(!irqs_disabled());
> +
> + ret = __rcu_needs_cpu(&rcu_global_state_normal, &per_cpu(rcu_cpudata_normal, cpu)) ||
> + __rcu_needs_cpu(&rcu_global_state_bh, &per_cpu(rcu_cpudata_bh, cpu)) ||
> + (per_cpu(rcu_cpudata_dead, cpu).deadqlen > 0);
> +
> + return ret;
> +}
> +
> +/**
> + * rcu_check_callback(cpu, user) - external entry point for grace checking
> + * @cpu: cpu id.
> + * @user: user space was interrupted.
> + *
> + * Top-level function driving RCU grace-period detection, normally
> + * invoked from the scheduler-clock interrupt. This function simply
> + * increments counters that are read only from softirq by this same
> + * CPU, so there are no memory barriers required.
> + *
> + * This function can run with disabled local interrupts, thus all
> + * callees must use local_irq_save()
> + */
> +void rcu_check_callbacks(int cpu, int user)
> +{
> + if (user ||
> + (idle_cpu(cpu) && !in_softirq() &&
> + hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
> +
> + /*
> + * Get here if this CPU took its interrupt from user
> + * mode or from the idle loop, and if this is not a
> + * nested interrupt. In this case, the CPU is in
> + * a quiescent state, so count it.
> + *
> + */
> + rcu_state_machine(&rcu_global_state_normal, &per_cpu(rcu_cpudata_normal, cpu), 1, cpu);
> + rcu_state_machine(&rcu_global_state_bh, &per_cpu(rcu_cpudata_bh, cpu), 1, cpu);
> +
> + } else if (!in_softirq()) {
> +
> + /*
> + * Get here if this CPU did not take its interrupt from
> + * softirq, in other words, if it is not interrupting
> + * a rcu_bh read-side critical section. This is an _bh
> + * critical section, so count it.
> + */
> + rcu_state_machine(&rcu_global_state_normal, &per_cpu(rcu_cpudata_normal, cpu), 0, cpu);
> + rcu_state_machine(&rcu_global_state_bh, &per_cpu(rcu_cpudata_bh, cpu), 1, cpu);
> + } else {
> + /*
> + * We are interrupting something. Nevertheless - check if we should collect
> + * rcu objects. This can be done from arbitrary context.
> + */
> + rcu_state_machine(&rcu_global_state_normal, &per_cpu(rcu_cpudata_normal, cpu), 0, cpu);
> + rcu_state_machine(&rcu_global_state_bh, &per_cpu(rcu_cpudata_bh, cpu), 0, cpu);
> + }
> +}
> +
> +/*
> + * Invoke the completed RCU callbacks.
> + */
> +static void rcu_do_batch(struct rcu_cpu_dead *rcd)
> +{
> + struct rcu_head *list;
> + int i, count;
> +
> + if (!rcd->deadqlen)
> + return;
> +
> + /* step 1: pull up to rcs->batchcount objects */
> + BUG_ON(irqs_disabled());
> + local_irq_disable();
> +
> + if (rcd->deadqlen > rcd->batchcount) {
> + struct rcu_head *walk;
> +
> + list = rcd->dead;
> + count = rcd->batchcount;
> +
> + walk = rcd->dead;
> + for (i=0;i<count;i++)
> + walk = walk->next;
> + rcd->dead = walk;
> +
> + } else {
> + list = rcd->dead;
> + count = rcd->deadqlen;
> +
> + rcd->dead = NULL;
> + rcd->deadtail = NULL;
> + }
> + rcd->deadqlen -= count;
> + BUG_ON(rcd->deadqlen < 0);
> +
> + local_irq_enable();
> +
> + /* step 2: call the rcu callbacks */
> +
> + for (i=0;i<count;i++) {
> + struct rcu_head *next;
> +
> + next = list->next;
> + prefetch(next);
> + list->func(list);
> + list = next;
> + }
> +
> + /* step 3: if still entries left, raise the softirq again */
> + if (rcd->deadqlen)
> + raise_softirq(RCU_SOFTIRQ);
> +}
> +
> +static void rcu_process_callbacks(struct softirq_action *unused)
> +{
> + rcu_do_batch(&get_cpu_var(rcu_cpudata_dead));
> + put_cpu_var(rcu_cpudata_dead);
> +}
> +
> +static void __rcu_add_cpu(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs, int cpu)
> +{
> + rcs->state = rcu_cpumask_addcpu(&rgs->cpus, cpu);
> +}
> +
> +#ifdef CONFIG_NO_HZ
> +
> +void rcu_enter_nohz(void)
> +{
> + int cpu = smp_processor_id();
> + int *pmode;
> +
> + /*
> + * call_rcu() between rcu_needs_cpu and rcu_enter_nohz() are
> + * not permitted.
> + * Thus both must be called with disabled local interrupts,
> + * without enabling the interrupts in between.
> + *
> + * Note: disabling interrupts only prevents call_rcu().
> + * it can obviously happen that another cpu forwards
> + * the state machine. That doesn't hurt: __rcu_remove_cpu()
> + * the the work that we need to do.
> + */
> + BUG_ON(!irqs_disabled());
> +
> + pmode = &get_cpu_var(rcu_cpumode);
> + BUG_ON(*pmode != RCU_CPUMODE_DELAYED);
> + *pmode = 0;
> + put_cpu_var(rcu_cpumode);
> +
> + __rcu_remove_cpu(&rcu_global_state_normal, &get_cpu_var(rcu_cpudata_normal), cpu);
> + put_cpu_var(rcu_cpudata_normal);
> + __rcu_remove_cpu(&rcu_global_state_bh, &get_cpu_var(rcu_cpudata_bh), cpu);
> + put_cpu_var(rcu_cpudata_bh);
> +
> + BUG_ON(rcu_needs_cpu(cpu));
> +}
> +
> +void rcu_exit_nohz(void)
> +{
> + int cpu = smp_processor_id();
> + int *pmode;
> +
> + BUG_ON(!irqs_disabled());
> +
> + pmode = &get_cpu_var(rcu_cpumode);
> + BUG_ON(*pmode != 0);
> + *pmode = RCU_CPUMODE_DELAYED;
> + put_cpu_var(rcu_cpumode);
> +
> + __rcu_add_cpu(&rcu_global_state_normal, &get_cpu_var(rcu_cpudata_normal), cpu);
> + put_cpu_var(rcu_cpudata_normal);
> + __rcu_add_cpu(&rcu_global_state_bh, &get_cpu_var(rcu_cpudata_bh), cpu);
> + put_cpu_var(rcu_cpudata_bh);
> +}
> +
> +void rcu_irq_enter(int in_nmi)
> +{
> + int *pmode;
> +
> + BUG_ON(!irqs_disabled());
> +
> + pmode = &get_cpu_var(rcu_cpumode);
> + if (unlikely(*pmode != RCU_CPUMODE_DELAYED)) {
> + if (in_nmi) {
> + int *pcount;
> +
> + pcount = &get_cpu_var(rcu_nmi_counter_percpu);
> + (*pcount)++;
> + put_cpu_var(rcu_nmi_counter_percpu);
> + atomic_inc(&rcu_nmi_counter);
> + /*
> + * Here an explicit mb() is required:
> + * All other memory ordering is enforced by the
> + * spinlock in rgs->cpus. For NMIs, this is not
> + * the case: The counters inc must be before
> + * any accesses to rcu protected memory,
> + * the counter dec after all accesses.
> + */
> + smp_mb();
> + } else {
> + if (*pmode == 0) {
> + int cpu = smp_processor_id();
> +
> + __rcu_add_cpu(&rcu_global_state_normal,&get_cpu_var(rcu_cpudata_normal), cpu);
> + put_cpu_var(rcu_cpudata_normal);
> + __rcu_add_cpu(&rcu_global_state_bh,&get_cpu_var(rcu_cpudata_bh), cpu);
> + put_cpu_var(rcu_cpudata_bh);
> + }
> + (*pmode)++;
> + }
> + }
> + put_cpu_var(rcu_cpumode);
> +}
> +
> +void rcu_irq_exit(int in_nmi)
> +{
> + int *pmode;
> +
> + BUG_ON(!irqs_disabled());
> +
> + pmode = &get_cpu_var(rcu_cpumode);
> + if (unlikely(*pmode != RCU_CPUMODE_DELAYED)) {
> + if (in_nmi) {
> + int *pcount;
> + /* see comment in rcu_irq_enter() */
> + smp_mb();
> +
> + atomic_dec(&rcu_nmi_counter);
> +
> + pcount = &get_cpu_var(rcu_nmi_counter_percpu);
> + (*pcount)--;
> + put_cpu_var(rcu_nmi_counter_percpu);
> + } else {
> + (*pmode)--;
> +
> + if (*pmode == 0) {
> + int cpu = smp_processor_id();
> +
> + /*
> + * task 1: remove us from the list of cpus that might be inside critical
> + * sections and inform the global state machine that we are outside
> + * any read side critical sections.
> + */
> + __rcu_remove_cpu(&rcu_global_state_normal,&per_cpu(rcu_cpudata_normal, cpu), cpu);
> + __rcu_remove_cpu(&rcu_global_state_bh,&per_cpu(rcu_cpudata_bh, cpu), cpu);
> +
> + if (rcu_needs_cpu(cpu)) {
> + /*
> + * task 2: Someone did a call_rcu() in the interupt.
> + * Duh, we've lost. Force a reschedule, that leaves nohz mode.
> + *
> + * Note: This can race: our call_rcu() might have set
> + * start_immediately. But: that start might happen before
> + * we readd ourself to the global cpu mask. Then we would
> + * not take part in the global cycle - and we would not set
> + * start_immediately again, either, because our newqlen is
> + * already above qlowmark. The timeout would
> + * ensure forward progress, thus it's not that bad.
> + *
> + * FIXME: double check that this really works.
> + */
> +printk(KERN_ERR" irq exit %d - need resched .\n", cpu);
> + set_need_resched();
> + }
> + }
> + }
> + }
> +}
> +
> +#endif /* CONFIG_NO_HZ */
> +
> +static void rcu_init_percpu_data(struct rcu_global_state *rgs, struct rcu_cpu_state *rcs, int cpu)
> +{
> + __rcu_add_cpu(rgs, rcs, cpu);
> +
> + rcs->new = rcs->old = NULL;
> + rcs->newqlen = rcs->oldqlen = 0;
> +}
> +
> +static void __cpuinit rcu_online_cpu(int cpu)
> +{
> + rcu_init_percpu_data(&rcu_global_state_normal, &per_cpu(rcu_cpudata_normal, cpu), cpu);
> + rcu_init_percpu_data(&rcu_global_state_bh, &per_cpu(rcu_cpudata_bh, cpu), cpu);
> +
> + per_cpu(rcu_cpumode, cpu) = RCU_CPUMODE_DELAYED;
> +
> + per_cpu(rcu_cpudata_dead, cpu).dead = NULL;
> + per_cpu(rcu_cpudata_dead, cpu).deadqlen = 0;
> + per_cpu(rcu_cpudata_dead, cpu).batchcount = RCU_BATCH_MIN;
> +
> + open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
> +}
> +
> +static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
> + unsigned long action, void *hcpu)
> +{
> + long cpu = (long)hcpu;
> +
> + switch (action) {
> + case CPU_UP_PREPARE:
> + case CPU_UP_PREPARE_FROZEN:
> + rcu_online_cpu(cpu);
> + break;
> + case CPU_UP_CANCELED:
> + case CPU_UP_CANCELED_FROZEN:
> + /*
> + * During CPU_UP_PREPARE, the cpu is fully accounted for
> + * and added into the rcu_cpumask. Thus it must be properly
> + * removed if the CPU_UP failed.
> + * Therefore CPU_UP_CANCELED is equivalent to CPU_DEAD.
> + */
> + /* fall-through */
> + case CPU_DEAD:
> + case CPU_DEAD_FROZEN:
> + rcu_offline_cpu(cpu);
> + break;
> + default:
> + break;
> + }
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block __cpuinitdata rcu_nb = {
> + .notifier_call = rcu_cpu_notify,
> +};
> +
> +/*
> + * Initializes rcu mechanism. Assumed to be called early.
> + * That is before local timer(SMP) or jiffie timer (uniproc) is setup.
> + * Note that rcu_qsctr and friends are implicitly
> + * initialized due to the choice of ``0'' for RCU_CTR_INVALID.
> + */
> +void __init __rcu_init(void)
> +{
> + rcu_cpumask_init(&rcu_global_state_normal.cpus, RCU_STATE_DESTROY, 0);
> + rcu_cpumask_init(&rcu_global_state_bh.cpus, RCU_STATE_DESTROY, 0);
> + rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
> + (void *)(long)smp_processor_id());
> + /* Register notifier for non-boot CPUs */
> + register_cpu_notifier(&rcu_nb);
> +}
> +
> +module_param(qlowmark, int, 0);
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index c506f26..ba20a90 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -287,7 +287,7 @@ void irq_exit(void)
> /* Make sure that timer wheel updates are propagated */
> if (!in_interrupt() && idle_cpu(smp_processor_id()) && !need_resched())
> tick_nohz_stop_sched_tick(0);
> - rcu_irq_exit();
> + rcu_irq_exit(0);
> #endif
> preempt_enable_no_resched();
> }
> --
> 1.5.5.1
>
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