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linux-next/kernel/rcupreempt.c
Paul E. McKenney c9e71002aa rcupreempt: remove never-migrates assumption from rcu_process_callbacks()
This patch fixes a potentially invalid access to a per-CPU variable in
rcu_process_callbacks().

This per-CPU access needs to be done in such a way as to guarantee that
the code using it cannot move to some other CPU before all uses of the
value accessed have completed.  Even though this code is currently only
invoked from softirq context, which currrently cannot migrate to some
other CPU, life would be better if this code did not silently make such
an assumption.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-29 20:21:13 +01:00

1173 lines
32 KiB
C

/*
* Read-Copy Update mechanism for mutual exclusion, realtime implementation
*
* 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, 2006
*
* Authors: Paul E. McKenney <paulmck@us.ibm.com>
* With thanks to Esben Nielsen, Bill Huey, and Ingo Molnar
* for pushing me away from locks and towards counters, and
* to Suparna Bhattacharya for pushing me completely away
* from atomic instructions on the read side.
*
* - Added handling of Dynamic Ticks
* Copyright 2007 - Paul E. Mckenney <paulmck@us.ibm.com>
* - Steven Rostedt <srostedt@redhat.com>
*
* Papers: http://www.rdrop.com/users/paulmck/RCU
*
* Design Document: http://lwn.net/Articles/253651/
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU/ *.txt
*
*/
#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/rcupdate.h>
#include <linux/cpu.h>
#include <linux/random.h>
#include <linux/delay.h>
#include <linux/byteorder/swabb.h>
#include <linux/cpumask.h>
#include <linux/rcupreempt_trace.h>
/*
* Macro that prevents the compiler from reordering accesses, but does
* absolutely -nothing- to prevent CPUs from reordering. This is used
* only to mediate communication between mainline code and hardware
* interrupt and NMI handlers.
*/
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
/*
* PREEMPT_RCU data structures.
*/
/*
* GP_STAGES specifies the number of times the state machine has
* to go through the all the rcu_try_flip_states (see below)
* in a single Grace Period.
*
* GP in GP_STAGES stands for Grace Period ;)
*/
#define GP_STAGES 2
struct rcu_data {
spinlock_t lock; /* Protect rcu_data fields. */
long completed; /* Number of last completed batch. */
int waitlistcount;
struct tasklet_struct rcu_tasklet;
struct rcu_head *nextlist;
struct rcu_head **nexttail;
struct rcu_head *waitlist[GP_STAGES];
struct rcu_head **waittail[GP_STAGES];
struct rcu_head *donelist;
struct rcu_head **donetail;
long rcu_flipctr[2];
#ifdef CONFIG_RCU_TRACE
struct rcupreempt_trace trace;
#endif /* #ifdef CONFIG_RCU_TRACE */
};
/*
* States for rcu_try_flip() and friends.
*/
enum rcu_try_flip_states {
/*
* Stay here if nothing is happening. Flip the counter if somthing
* starts happening. Denoted by "I"
*/
rcu_try_flip_idle_state,
/*
* Wait here for all CPUs to notice that the counter has flipped. This
* prevents the old set of counters from ever being incremented once
* we leave this state, which in turn is necessary because we cannot
* test any individual counter for zero -- we can only check the sum.
* Denoted by "A".
*/
rcu_try_flip_waitack_state,
/*
* Wait here for the sum of the old per-CPU counters to reach zero.
* Denoted by "Z".
*/
rcu_try_flip_waitzero_state,
/*
* Wait here for each of the other CPUs to execute a memory barrier.
* This is necessary to ensure that these other CPUs really have
* completed executing their RCU read-side critical sections, despite
* their CPUs wildly reordering memory. Denoted by "M".
*/
rcu_try_flip_waitmb_state,
};
struct rcu_ctrlblk {
spinlock_t fliplock; /* Protect state-machine transitions. */
long completed; /* Number of last completed batch. */
enum rcu_try_flip_states rcu_try_flip_state; /* The current state of
the rcu state machine */
};
static DEFINE_PER_CPU(struct rcu_data, rcu_data);
static struct rcu_ctrlblk rcu_ctrlblk = {
.fliplock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.fliplock),
.completed = 0,
.rcu_try_flip_state = rcu_try_flip_idle_state,
};
#ifdef CONFIG_RCU_TRACE
static char *rcu_try_flip_state_names[] =
{ "idle", "waitack", "waitzero", "waitmb" };
#endif /* #ifdef CONFIG_RCU_TRACE */
static cpumask_t rcu_cpu_online_map __read_mostly = CPU_MASK_NONE;
/*
* Enum and per-CPU flag to determine when each CPU has seen
* the most recent counter flip.
*/
enum rcu_flip_flag_values {
rcu_flip_seen, /* Steady/initial state, last flip seen. */
/* Only GP detector can update. */
rcu_flipped /* Flip just completed, need confirmation. */
/* Only corresponding CPU can update. */
};
static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_flip_flag_values, rcu_flip_flag)
= rcu_flip_seen;
/*
* Enum and per-CPU flag to determine when each CPU has executed the
* needed memory barrier to fence in memory references from its last RCU
* read-side critical section in the just-completed grace period.
*/
enum rcu_mb_flag_values {
rcu_mb_done, /* Steady/initial state, no mb()s required. */
/* Only GP detector can update. */
rcu_mb_needed /* Flip just completed, need an mb(). */
/* Only corresponding CPU can update. */
};
static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_mb_flag_values, rcu_mb_flag)
= rcu_mb_done;
/*
* RCU_DATA_ME: find the current CPU's rcu_data structure.
* RCU_DATA_CPU: find the specified CPU's rcu_data structure.
*/
#define RCU_DATA_ME() (&__get_cpu_var(rcu_data))
#define RCU_DATA_CPU(cpu) (&per_cpu(rcu_data, cpu))
/*
* Helper macro for tracing when the appropriate rcu_data is not
* cached in a local variable, but where the CPU number is so cached.
*/
#define RCU_TRACE_CPU(f, cpu) RCU_TRACE(f, &(RCU_DATA_CPU(cpu)->trace));
/*
* Helper macro for tracing when the appropriate rcu_data is not
* cached in a local variable.
*/
#define RCU_TRACE_ME(f) RCU_TRACE(f, &(RCU_DATA_ME()->trace));
/*
* Helper macro for tracing when the appropriate rcu_data is pointed
* to by a local variable.
*/
#define RCU_TRACE_RDP(f, rdp) RCU_TRACE(f, &((rdp)->trace));
/*
* Return the number of RCU batches processed thus far. Useful
* for debug and statistics.
*/
long rcu_batches_completed(void)
{
return rcu_ctrlblk.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
void __rcu_read_lock(void)
{
int idx;
struct task_struct *t = current;
int nesting;
nesting = ACCESS_ONCE(t->rcu_read_lock_nesting);
if (nesting != 0) {
/* An earlier rcu_read_lock() covers us, just count it. */
t->rcu_read_lock_nesting = nesting + 1;
} else {
unsigned long flags;
/*
* We disable interrupts for the following reasons:
* - If we get scheduling clock interrupt here, and we
* end up acking the counter flip, it's like a promise
* that we will never increment the old counter again.
* Thus we will break that promise if that
* scheduling clock interrupt happens between the time
* we pick the .completed field and the time that we
* increment our counter.
*
* - We don't want to be preempted out here.
*
* NMIs can still occur, of course, and might themselves
* contain rcu_read_lock().
*/
local_irq_save(flags);
/*
* Outermost nesting of rcu_read_lock(), so increment
* the current counter for the current CPU. Use volatile
* casts to prevent the compiler from reordering.
*/
idx = ACCESS_ONCE(rcu_ctrlblk.completed) & 0x1;
ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])++;
/*
* Now that the per-CPU counter has been incremented, we
* are protected from races with rcu_read_lock() invoked
* from NMI handlers on this CPU. We can therefore safely
* increment the nesting counter, relieving further NMIs
* of the need to increment the per-CPU counter.
*/
ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting + 1;
/*
* Now that we have preventing any NMIs from storing
* to the ->rcu_flipctr_idx, we can safely use it to
* remember which counter to decrement in the matching
* rcu_read_unlock().
*/
ACCESS_ONCE(t->rcu_flipctr_idx) = idx;
local_irq_restore(flags);
}
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);
void __rcu_read_unlock(void)
{
int idx;
struct task_struct *t = current;
int nesting;
nesting = ACCESS_ONCE(t->rcu_read_lock_nesting);
if (nesting > 1) {
/*
* We are still protected by the enclosing rcu_read_lock(),
* so simply decrement the counter.
*/
t->rcu_read_lock_nesting = nesting - 1;
} else {
unsigned long flags;
/*
* Disable local interrupts to prevent the grace-period
* detection state machine from seeing us half-done.
* NMIs can still occur, of course, and might themselves
* contain rcu_read_lock() and rcu_read_unlock().
*/
local_irq_save(flags);
/*
* Outermost nesting of rcu_read_unlock(), so we must
* decrement the current counter for the current CPU.
* This must be done carefully, because NMIs can
* occur at any point in this code, and any rcu_read_lock()
* and rcu_read_unlock() pairs in the NMI handlers
* must interact non-destructively with this code.
* Lots of volatile casts, and -very- careful ordering.
*
* Changes to this code, including this one, must be
* inspected, validated, and tested extremely carefully!!!
*/
/*
* First, pick up the index.
*/
idx = ACCESS_ONCE(t->rcu_flipctr_idx);
/*
* Now that we have fetched the counter index, it is
* safe to decrement the per-task RCU nesting counter.
* After this, any interrupts or NMIs will increment and
* decrement the per-CPU counters.
*/
ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting - 1;
/*
* It is now safe to decrement this task's nesting count.
* NMIs that occur after this statement will route their
* rcu_read_lock() calls through this "else" clause, and
* will thus start incrementing the per-CPU counter on
* their own. They will also clobber ->rcu_flipctr_idx,
* but that is OK, since we have already fetched it.
*/
ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])--;
local_irq_restore(flags);
}
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
/*
* If a global counter flip has occurred since the last time that we
* advanced callbacks, advance them. Hardware interrupts must be
* disabled when calling this function.
*/
static void __rcu_advance_callbacks(struct rcu_data *rdp)
{
int cpu;
int i;
int wlc = 0;
if (rdp->completed != rcu_ctrlblk.completed) {
if (rdp->waitlist[GP_STAGES - 1] != NULL) {
*rdp->donetail = rdp->waitlist[GP_STAGES - 1];
rdp->donetail = rdp->waittail[GP_STAGES - 1];
RCU_TRACE_RDP(rcupreempt_trace_move2done, rdp);
}
for (i = GP_STAGES - 2; i >= 0; i--) {
if (rdp->waitlist[i] != NULL) {
rdp->waitlist[i + 1] = rdp->waitlist[i];
rdp->waittail[i + 1] = rdp->waittail[i];
wlc++;
} else {
rdp->waitlist[i + 1] = NULL;
rdp->waittail[i + 1] =
&rdp->waitlist[i + 1];
}
}
if (rdp->nextlist != NULL) {
rdp->waitlist[0] = rdp->nextlist;
rdp->waittail[0] = rdp->nexttail;
wlc++;
rdp->nextlist = NULL;
rdp->nexttail = &rdp->nextlist;
RCU_TRACE_RDP(rcupreempt_trace_move2wait, rdp);
} else {
rdp->waitlist[0] = NULL;
rdp->waittail[0] = &rdp->waitlist[0];
}
rdp->waitlistcount = wlc;
rdp->completed = rcu_ctrlblk.completed;
}
/*
* Check to see if this CPU needs to report that it has seen
* the most recent counter flip, thereby declaring that all
* subsequent rcu_read_lock() invocations will respect this flip.
*/
cpu = raw_smp_processor_id();
if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) {
smp_mb(); /* Subsequent counter accesses must see new value */
per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen;
smp_mb(); /* Subsequent RCU read-side critical sections */
/* seen -after- acknowledgement. */
}
}
#ifdef CONFIG_NO_HZ
DEFINE_PER_CPU(long, dynticks_progress_counter) = 1;
static DEFINE_PER_CPU(long, rcu_dyntick_snapshot);
static DEFINE_PER_CPU(int, rcu_update_flag);
/**
* rcu_irq_enter - Called from Hard irq handlers and NMI/SMI.
*
* If the CPU was idle with dynamic ticks active, this updates the
* dynticks_progress_counter to let the RCU handling know that the
* CPU is active.
*/
void rcu_irq_enter(void)
{
int cpu = smp_processor_id();
if (per_cpu(rcu_update_flag, cpu))
per_cpu(rcu_update_flag, cpu)++;
/*
* Only update if we are coming from a stopped ticks mode
* (dynticks_progress_counter is even).
*/
if (!in_interrupt() &&
(per_cpu(dynticks_progress_counter, cpu) & 0x1) == 0) {
/*
* The following might seem like we could have a race
* with NMI/SMIs. But this really isn't a problem.
* Here we do a read/modify/write, and the race happens
* when an NMI/SMI comes in after the read and before
* the write. But NMI/SMIs will increment this counter
* twice before returning, so the zero bit will not
* be corrupted by the NMI/SMI which is the most important
* part.
*
* The only thing is that we would bring back the counter
* to a postion that it was in during the NMI/SMI.
* But the zero bit would be set, so the rest of the
* counter would again be ignored.
*
* On return from the IRQ, the counter may have the zero
* bit be 0 and the counter the same as the return from
* the NMI/SMI. If the state machine was so unlucky to
* see that, it still doesn't matter, since all
* RCU read-side critical sections on this CPU would
* have already completed.
*/
per_cpu(dynticks_progress_counter, cpu)++;
/*
* The following memory barrier ensures that any
* rcu_read_lock() primitives in the irq handler
* are seen by other CPUs to follow the above
* increment to dynticks_progress_counter. This is
* required in order for other CPUs to correctly
* determine when it is safe to advance the RCU
* grace-period state machine.
*/
smp_mb(); /* see above block comment. */
/*
* Since we can't determine the dynamic tick mode from
* the dynticks_progress_counter after this routine,
* we use a second flag to acknowledge that we came
* from an idle state with ticks stopped.
*/
per_cpu(rcu_update_flag, cpu)++;
/*
* If we take an NMI/SMI now, they will also increment
* the rcu_update_flag, and will not update the
* dynticks_progress_counter on exit. That is for
* this IRQ to do.
*/
}
}
/**
* rcu_irq_exit - Called from exiting Hard irq context.
*
* If the CPU was idle with dynamic ticks active, update the
* dynticks_progress_counter to put let the RCU handling be
* aware that the CPU is going back to idle with no ticks.
*/
void rcu_irq_exit(void)
{
int cpu = smp_processor_id();
/*
* rcu_update_flag is set if we interrupted the CPU
* when it was idle with ticks stopped.
* Once this occurs, we keep track of interrupt nesting
* because a NMI/SMI could also come in, and we still
* only want the IRQ that started the increment of the
* dynticks_progress_counter to be the one that modifies
* it on exit.
*/
if (per_cpu(rcu_update_flag, cpu)) {
if (--per_cpu(rcu_update_flag, cpu))
return;
/* This must match the interrupt nesting */
WARN_ON(in_interrupt());
/*
* If an NMI/SMI happens now we are still
* protected by the dynticks_progress_counter being odd.
*/
/*
* The following memory barrier ensures that any
* rcu_read_unlock() primitives in the irq handler
* are seen by other CPUs to preceed the following
* increment to dynticks_progress_counter. This
* is required in order for other CPUs to determine
* when it is safe to advance the RCU grace-period
* state machine.
*/
smp_mb(); /* see above block comment. */
per_cpu(dynticks_progress_counter, cpu)++;
WARN_ON(per_cpu(dynticks_progress_counter, cpu) & 0x1);
}
}
static void dyntick_save_progress_counter(int cpu)
{
per_cpu(rcu_dyntick_snapshot, cpu) =
per_cpu(dynticks_progress_counter, cpu);
}
static inline int
rcu_try_flip_waitack_needed(int cpu)
{
long curr;
long snap;
curr = per_cpu(dynticks_progress_counter, cpu);
snap = per_cpu(rcu_dyntick_snapshot, cpu);
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
/*
* If the CPU remained in dynticks mode for the entire time
* and didn't take any interrupts, NMIs, SMIs, or whatever,
* then it cannot be in the middle of an rcu_read_lock(), so
* the next rcu_read_lock() it executes must use the new value
* of the counter. So we can safely pretend that this CPU
* already acknowledged the counter.
*/
if ((curr == snap) && ((curr & 0x1) == 0))
return 0;
/*
* If the CPU passed through or entered a dynticks idle phase with
* no active irq handlers, then, as above, we can safely pretend
* that this CPU already acknowledged the counter.
*/
if ((curr - snap) > 2 || (snap & 0x1) == 0)
return 0;
/* We need this CPU to explicitly acknowledge the counter flip. */
return 1;
}
static inline int
rcu_try_flip_waitmb_needed(int cpu)
{
long curr;
long snap;
curr = per_cpu(dynticks_progress_counter, cpu);
snap = per_cpu(rcu_dyntick_snapshot, cpu);
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
/*
* If the CPU remained in dynticks mode for the entire time
* and didn't take any interrupts, NMIs, SMIs, or whatever,
* then it cannot have executed an RCU read-side critical section
* during that time, so there is no need for it to execute a
* memory barrier.
*/
if ((curr == snap) && ((curr & 0x1) == 0))
return 0;
/*
* If the CPU either entered or exited an outermost interrupt,
* SMI, NMI, or whatever handler, then we know that it executed
* a memory barrier when doing so. So we don't need another one.
*/
if (curr != snap)
return 0;
/* We need the CPU to execute a memory barrier. */
return 1;
}
#else /* !CONFIG_NO_HZ */
# define dyntick_save_progress_counter(cpu) do { } while (0)
# define rcu_try_flip_waitack_needed(cpu) (1)
# define rcu_try_flip_waitmb_needed(cpu) (1)
#endif /* CONFIG_NO_HZ */
/*
* Get here when RCU is idle. Decide whether we need to
* move out of idle state, and return non-zero if so.
* "Straightforward" approach for the moment, might later
* use callback-list lengths, grace-period duration, or
* some such to determine when to exit idle state.
* Might also need a pre-idle test that does not acquire
* the lock, but let's get the simple case working first...
*/
static int
rcu_try_flip_idle(void)
{
int cpu;
RCU_TRACE_ME(rcupreempt_trace_try_flip_i1);
if (!rcu_pending(smp_processor_id())) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_ie1);
return 0;
}
/*
* Do the flip.
*/
RCU_TRACE_ME(rcupreempt_trace_try_flip_g1);
rcu_ctrlblk.completed++; /* stands in for rcu_try_flip_g2 */
/*
* Need a memory barrier so that other CPUs see the new
* counter value before they see the subsequent change of all
* the rcu_flip_flag instances to rcu_flipped.
*/
smp_mb(); /* see above block comment. */
/* Now ask each CPU for acknowledgement of the flip. */
for_each_cpu_mask(cpu, rcu_cpu_online_map) {
per_cpu(rcu_flip_flag, cpu) = rcu_flipped;
dyntick_save_progress_counter(cpu);
}
return 1;
}
/*
* Wait for CPUs to acknowledge the flip.
*/
static int
rcu_try_flip_waitack(void)
{
int cpu;
RCU_TRACE_ME(rcupreempt_trace_try_flip_a1);
for_each_cpu_mask(cpu, rcu_cpu_online_map)
if (rcu_try_flip_waitack_needed(cpu) &&
per_cpu(rcu_flip_flag, cpu) != rcu_flip_seen) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_ae1);
return 0;
}
/*
* Make sure our checks above don't bleed into subsequent
* waiting for the sum of the counters to reach zero.
*/
smp_mb(); /* see above block comment. */
RCU_TRACE_ME(rcupreempt_trace_try_flip_a2);
return 1;
}
/*
* Wait for collective ``last'' counter to reach zero,
* then tell all CPUs to do an end-of-grace-period memory barrier.
*/
static int
rcu_try_flip_waitzero(void)
{
int cpu;
int lastidx = !(rcu_ctrlblk.completed & 0x1);
int sum = 0;
/* Check to see if the sum of the "last" counters is zero. */
RCU_TRACE_ME(rcupreempt_trace_try_flip_z1);
for_each_cpu_mask(cpu, rcu_cpu_online_map)
sum += RCU_DATA_CPU(cpu)->rcu_flipctr[lastidx];
if (sum != 0) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_ze1);
return 0;
}
/*
* This ensures that the other CPUs see the call for
* memory barriers -after- the sum to zero has been
* detected here
*/
smp_mb(); /* ^^^^^^^^^^^^ */
/* Call for a memory barrier from each CPU. */
for_each_cpu_mask(cpu, rcu_cpu_online_map) {
per_cpu(rcu_mb_flag, cpu) = rcu_mb_needed;
dyntick_save_progress_counter(cpu);
}
RCU_TRACE_ME(rcupreempt_trace_try_flip_z2);
return 1;
}
/*
* Wait for all CPUs to do their end-of-grace-period memory barrier.
* Return 0 once all CPUs have done so.
*/
static int
rcu_try_flip_waitmb(void)
{
int cpu;
RCU_TRACE_ME(rcupreempt_trace_try_flip_m1);
for_each_cpu_mask(cpu, rcu_cpu_online_map)
if (rcu_try_flip_waitmb_needed(cpu) &&
per_cpu(rcu_mb_flag, cpu) != rcu_mb_done) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_me1);
return 0;
}
smp_mb(); /* Ensure that the above checks precede any following flip. */
RCU_TRACE_ME(rcupreempt_trace_try_flip_m2);
return 1;
}
/*
* Attempt a single flip of the counters. Remember, a single flip does
* -not- constitute a grace period. Instead, the interval between
* at least GP_STAGES consecutive flips is a grace period.
*
* If anyone is nuts enough to run this CONFIG_PREEMPT_RCU implementation
* on a large SMP, they might want to use a hierarchical organization of
* the per-CPU-counter pairs.
*/
static void rcu_try_flip(void)
{
unsigned long flags;
RCU_TRACE_ME(rcupreempt_trace_try_flip_1);
if (unlikely(!spin_trylock_irqsave(&rcu_ctrlblk.fliplock, flags))) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_e1);
return;
}
/*
* Take the next transition(s) through the RCU grace-period
* flip-counter state machine.
*/
switch (rcu_ctrlblk.rcu_try_flip_state) {
case rcu_try_flip_idle_state:
if (rcu_try_flip_idle())
rcu_ctrlblk.rcu_try_flip_state =
rcu_try_flip_waitack_state;
break;
case rcu_try_flip_waitack_state:
if (rcu_try_flip_waitack())
rcu_ctrlblk.rcu_try_flip_state =
rcu_try_flip_waitzero_state;
break;
case rcu_try_flip_waitzero_state:
if (rcu_try_flip_waitzero())
rcu_ctrlblk.rcu_try_flip_state =
rcu_try_flip_waitmb_state;
break;
case rcu_try_flip_waitmb_state:
if (rcu_try_flip_waitmb())
rcu_ctrlblk.rcu_try_flip_state =
rcu_try_flip_idle_state;
}
spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
}
/*
* Check to see if this CPU needs to do a memory barrier in order to
* ensure that any prior RCU read-side critical sections have committed
* their counter manipulations and critical-section memory references
* before declaring the grace period to be completed.
*/
static void rcu_check_mb(int cpu)
{
if (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed) {
smp_mb(); /* Ensure RCU read-side accesses are visible. */
per_cpu(rcu_mb_flag, cpu) = rcu_mb_done;
}
}
void rcu_check_callbacks(int cpu, int user)
{
unsigned long flags;
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
rcu_check_mb(cpu);
if (rcu_ctrlblk.completed == rdp->completed)
rcu_try_flip();
spin_lock_irqsave(&rdp->lock, flags);
RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
__rcu_advance_callbacks(rdp);
if (rdp->donelist == NULL) {
spin_unlock_irqrestore(&rdp->lock, flags);
} else {
spin_unlock_irqrestore(&rdp->lock, flags);
raise_softirq(RCU_SOFTIRQ);
}
}
/*
* Needed by dynticks, to make sure all RCU processing has finished
* when we go idle:
*/
void rcu_advance_callbacks(int cpu, int user)
{
unsigned long flags;
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
if (rcu_ctrlblk.completed == rdp->completed) {
rcu_try_flip();
if (rcu_ctrlblk.completed == rdp->completed)
return;
}
spin_lock_irqsave(&rdp->lock, flags);
RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
__rcu_advance_callbacks(rdp);
spin_unlock_irqrestore(&rdp->lock, flags);
}
#ifdef CONFIG_HOTPLUG_CPU
#define rcu_offline_cpu_enqueue(srclist, srctail, dstlist, dsttail) do { \
*dsttail = srclist; \
if (srclist != NULL) { \
dsttail = srctail; \
srclist = NULL; \
srctail = &srclist;\
} \
} while (0)
void rcu_offline_cpu(int cpu)
{
int i;
struct rcu_head *list = NULL;
unsigned long flags;
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
struct rcu_head **tail = &list;
/*
* Remove all callbacks from the newly dead CPU, retaining order.
* Otherwise rcu_barrier() will fail
*/
spin_lock_irqsave(&rdp->lock, flags);
rcu_offline_cpu_enqueue(rdp->donelist, rdp->donetail, list, tail);
for (i = GP_STAGES - 1; i >= 0; i--)
rcu_offline_cpu_enqueue(rdp->waitlist[i], rdp->waittail[i],
list, tail);
rcu_offline_cpu_enqueue(rdp->nextlist, rdp->nexttail, list, tail);
spin_unlock_irqrestore(&rdp->lock, flags);
rdp->waitlistcount = 0;
/* Disengage the newly dead CPU from the grace-period computation. */
spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
rcu_check_mb(cpu);
if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) {
smp_mb(); /* Subsequent counter accesses must see new value */
per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen;
smp_mb(); /* Subsequent RCU read-side critical sections */
/* seen -after- acknowledgement. */
}
RCU_DATA_ME()->rcu_flipctr[0] += RCU_DATA_CPU(cpu)->rcu_flipctr[0];
RCU_DATA_ME()->rcu_flipctr[1] += RCU_DATA_CPU(cpu)->rcu_flipctr[1];
RCU_DATA_CPU(cpu)->rcu_flipctr[0] = 0;
RCU_DATA_CPU(cpu)->rcu_flipctr[1] = 0;
cpu_clear(cpu, rcu_cpu_online_map);
spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
/*
* Place the removed callbacks on the current CPU's queue.
* Make them all start a new grace period: simple approach,
* in theory could starve a given set of callbacks, but
* you would need to be doing some serious CPU hotplugging
* to make this happen. If this becomes a problem, adding
* a synchronize_rcu() to the hotplug path would be a simple
* fix.
*/
local_irq_save(flags);
rdp = RCU_DATA_ME();
spin_lock(&rdp->lock);
*rdp->nexttail = list;
if (list)
rdp->nexttail = tail;
spin_unlock_irqrestore(&rdp->lock, flags);
}
void __devinit rcu_online_cpu(int cpu)
{
unsigned long flags;
spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
cpu_set(cpu, rcu_cpu_online_map);
spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
}
#else /* #ifdef CONFIG_HOTPLUG_CPU */
void rcu_offline_cpu(int cpu)
{
}
void __devinit rcu_online_cpu(int cpu)
{
}
#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_process_callbacks(struct softirq_action *unused)
{
unsigned long flags;
struct rcu_head *next, *list;
struct rcu_data *rdp;
local_irq_save(flags);
rdp = RCU_DATA_ME();
spin_lock(&rdp->lock);
list = rdp->donelist;
if (list == NULL) {
spin_unlock_irqrestore(&rdp->lock, flags);
return;
}
rdp->donelist = NULL;
rdp->donetail = &rdp->donelist;
RCU_TRACE_RDP(rcupreempt_trace_done_remove, rdp);
spin_unlock_irqrestore(&rdp->lock, flags);
while (list) {
next = list->next;
list->func(list);
list = next;
RCU_TRACE_ME(rcupreempt_trace_invoke);
}
}
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
unsigned long flags;
struct rcu_data *rdp;
head->func = func;
head->next = NULL;
local_irq_save(flags);
rdp = RCU_DATA_ME();
spin_lock(&rdp->lock);
__rcu_advance_callbacks(rdp);
*rdp->nexttail = head;
rdp->nexttail = &head->next;
RCU_TRACE_RDP(rcupreempt_trace_next_add, rdp);
spin_unlock(&rdp->lock);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(call_rcu);
/*
* 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.
*/
void __synchronize_sched(void)
{
cpumask_t oldmask;
int cpu;
if (sched_getaffinity(0, &oldmask) < 0)
oldmask = cpu_possible_map;
for_each_online_cpu(cpu) {
sched_setaffinity(0, cpumask_of_cpu(cpu));
schedule();
}
sched_setaffinity(0, oldmask);
}
EXPORT_SYMBOL_GPL(__synchronize_sched);
/*
* Check to see if any future RCU-related work will need to be done
* by the current CPU, even if none need be done immediately, returning
* 1 if so. Assumes that notifiers would take care of handling any
* outstanding requests from the RCU core.
*
* This function is part of the RCU implementation; it is -not-
* an exported member of the RCU API.
*/
int rcu_needs_cpu(int cpu)
{
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
return (rdp->donelist != NULL ||
!!rdp->waitlistcount ||
rdp->nextlist != NULL);
}
int rcu_pending(int cpu)
{
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
/* The CPU has at least one callback queued somewhere. */
if (rdp->donelist != NULL ||
!!rdp->waitlistcount ||
rdp->nextlist != NULL)
return 1;
/* The RCU core needs an acknowledgement from this CPU. */
if ((per_cpu(rcu_flip_flag, cpu) == rcu_flipped) ||
(per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed))
return 1;
/* This CPU has fallen behind the global grace-period number. */
if (rdp->completed != rcu_ctrlblk.completed)
return 1;
/* Nothing needed from this CPU. */
return 0;
}
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:
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,
};
void __init __rcu_init(void)
{
int cpu;
int i;
struct rcu_data *rdp;
printk(KERN_NOTICE "Preemptible RCU implementation.\n");
for_each_possible_cpu(cpu) {
rdp = RCU_DATA_CPU(cpu);
spin_lock_init(&rdp->lock);
rdp->completed = 0;
rdp->waitlistcount = 0;
rdp->nextlist = NULL;
rdp->nexttail = &rdp->nextlist;
for (i = 0; i < GP_STAGES; i++) {
rdp->waitlist[i] = NULL;
rdp->waittail[i] = &rdp->waitlist[i];
}
rdp->donelist = NULL;
rdp->donetail = &rdp->donelist;
rdp->rcu_flipctr[0] = 0;
rdp->rcu_flipctr[1] = 0;
}
register_cpu_notifier(&rcu_nb);
/*
* We don't need protection against CPU-Hotplug here
* since
* a) If a CPU comes online while we are iterating over the
* cpu_online_map below, we would only end up making a
* duplicate call to rcu_online_cpu() which sets the corresponding
* CPU's mask in the rcu_cpu_online_map.
*
* b) A CPU cannot go offline at this point in time since the user
* does not have access to the sysfs interface, nor do we
* suspend the system.
*/
for_each_online_cpu(cpu)
rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu);
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
}
/*
* Deprecated, use synchronize_rcu() or synchronize_sched() instead.
*/
void synchronize_kernel(void)
{
synchronize_rcu();
}
#ifdef CONFIG_RCU_TRACE
long *rcupreempt_flipctr(int cpu)
{
return &RCU_DATA_CPU(cpu)->rcu_flipctr[0];
}
EXPORT_SYMBOL_GPL(rcupreempt_flipctr);
int rcupreempt_flip_flag(int cpu)
{
return per_cpu(rcu_flip_flag, cpu);
}
EXPORT_SYMBOL_GPL(rcupreempt_flip_flag);
int rcupreempt_mb_flag(int cpu)
{
return per_cpu(rcu_mb_flag, cpu);
}
EXPORT_SYMBOL_GPL(rcupreempt_mb_flag);
char *rcupreempt_try_flip_state_name(void)
{
return rcu_try_flip_state_names[rcu_ctrlblk.rcu_try_flip_state];
}
EXPORT_SYMBOL_GPL(rcupreempt_try_flip_state_name);
struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu)
{
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
return &rdp->trace;
}
EXPORT_SYMBOL_GPL(rcupreempt_trace_cpu);
#endif /* #ifdef RCU_TRACE */