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authorIngo Molnar <mingo@elte.hu>2011-05-27 12:38:52 +0200
committerIngo Molnar <mingo@elte.hu>2011-05-28 17:41:05 +0200
commit29f742f88a32c9ab8cf6d9ba69e1ea918be5aa58 (patch)
treea38aa38c8025e050ec82a7e64d02dca07f90ffc7 /kernel/rcutree.c
parentDocumentation: Add statistics about nested locks (diff)
parentrcu: Decrease memory-barrier usage based on semi-formal proof (diff)
downloadlinux-29f742f88a32c9ab8cf6d9ba69e1ea918be5aa58.tar.xz
linux-29f742f88a32c9ab8cf6d9ba69e1ea918be5aa58.zip
Merge branch 'rcu/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu into core/urgent
Diffstat (limited to 'kernel/rcutree.c')
-rw-r--r--kernel/rcutree.c130
1 files changed, 56 insertions, 74 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f07d2f03181a..8154a4a3491c 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -163,7 +163,7 @@ EXPORT_SYMBOL_GPL(rcu_note_context_switch);
#ifdef CONFIG_NO_HZ
DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
.dynticks_nesting = 1,
- .dynticks = 1,
+ .dynticks = ATOMIC_INIT(1),
};
#endif /* #ifdef CONFIG_NO_HZ */
@@ -322,13 +322,25 @@ void rcu_enter_nohz(void)
unsigned long flags;
struct rcu_dynticks *rdtp;
- smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
- rdtp->dynticks++;
- rdtp->dynticks_nesting--;
- WARN_ON_ONCE(rdtp->dynticks & 0x1);
+ if (--rdtp->dynticks_nesting) {
+ local_irq_restore(flags);
+ return;
+ }
+ /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
+ smp_mb__before_atomic_inc(); /* See above. */
+ atomic_inc(&rdtp->dynticks);
+ smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
+ WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
local_irq_restore(flags);
+
+ /* If the interrupt queued a callback, get out of dyntick mode. */
+ if (in_irq() &&
+ (__get_cpu_var(rcu_sched_data).nxtlist ||
+ __get_cpu_var(rcu_bh_data).nxtlist ||
+ rcu_preempt_needs_cpu(smp_processor_id())))
+ set_need_resched();
}
/*
@@ -344,11 +356,16 @@ void rcu_exit_nohz(void)
local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
- rdtp->dynticks++;
- rdtp->dynticks_nesting++;
- WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
+ if (rdtp->dynticks_nesting++) {
+ local_irq_restore(flags);
+ return;
+ }
+ smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
+ atomic_inc(&rdtp->dynticks);
+ /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
+ smp_mb__after_atomic_inc(); /* See above. */
+ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
local_irq_restore(flags);
- smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}
/**
@@ -362,11 +379,15 @@ void rcu_nmi_enter(void)
{
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
- if (rdtp->dynticks & 0x1)
+ if (rdtp->dynticks_nmi_nesting == 0 &&
+ (atomic_read(&rdtp->dynticks) & 0x1))
return;
- rdtp->dynticks_nmi++;
- WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1));
- smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
+ rdtp->dynticks_nmi_nesting++;
+ smp_mb__before_atomic_inc(); /* Force delay from prior write. */
+ atomic_inc(&rdtp->dynticks);
+ /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
+ smp_mb__after_atomic_inc(); /* See above. */
+ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
}
/**
@@ -380,11 +401,14 @@ void rcu_nmi_exit(void)
{
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
- if (rdtp->dynticks & 0x1)
+ if (rdtp->dynticks_nmi_nesting == 0 ||
+ --rdtp->dynticks_nmi_nesting != 0)
return;
- smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
- rdtp->dynticks_nmi++;
- WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1);
+ /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
+ smp_mb__before_atomic_inc(); /* See above. */
+ atomic_inc(&rdtp->dynticks);
+ smp_mb__after_atomic_inc(); /* Force delay to next write. */
+ WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
}
/**
@@ -395,13 +419,7 @@ void rcu_nmi_exit(void)
*/
void rcu_irq_enter(void)
{
- struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
-
- if (rdtp->dynticks_nesting++)
- return;
- rdtp->dynticks++;
- WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
- smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
+ rcu_exit_nohz();
}
/**
@@ -413,18 +431,7 @@ void rcu_irq_enter(void)
*/
void rcu_irq_exit(void)
{
- struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
-
- if (--rdtp->dynticks_nesting)
- return;
- smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
- rdtp->dynticks++;
- WARN_ON_ONCE(rdtp->dynticks & 0x1);
-
- /* If the interrupt queued a callback, get out of dyntick mode. */
- if (__this_cpu_read(rcu_sched_data.nxtlist) ||
- __this_cpu_read(rcu_bh_data.nxtlist))
- set_need_resched();
+ rcu_enter_nohz();
}
#ifdef CONFIG_SMP
@@ -436,19 +443,8 @@ void rcu_irq_exit(void)
*/
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
- int ret;
- int snap;
- int snap_nmi;
-
- snap = rdp->dynticks->dynticks;
- snap_nmi = rdp->dynticks->dynticks_nmi;
- smp_mb(); /* Order sampling of snap with end of grace period. */
- rdp->dynticks_snap = snap;
- rdp->dynticks_nmi_snap = snap_nmi;
- ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
- if (ret)
- rdp->dynticks_fqs++;
- return ret;
+ rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
+ return 0;
}
/*
@@ -459,16 +455,11 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp)
*/
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
- long curr;
- long curr_nmi;
- long snap;
- long snap_nmi;
+ unsigned long curr;
+ unsigned long snap;
- curr = rdp->dynticks->dynticks;
- snap = rdp->dynticks_snap;
- curr_nmi = rdp->dynticks->dynticks_nmi;
- snap_nmi = rdp->dynticks_nmi_snap;
- smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
+ curr = (unsigned long)atomic_add_return(0, &rdp->dynticks->dynticks);
+ snap = (unsigned long)rdp->dynticks_snap;
/*
* If the CPU passed through or entered a dynticks idle phase with
@@ -478,8 +469,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
* read-side critical section that started before the beginning
* of the current RCU grace period.
*/
- if ((curr != snap || (curr & 0x1) == 0) &&
- (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
+ if ((curr & 0x1) == 0 || ULONG_CMP_GE(curr, snap + 2)) {
rdp->dynticks_fqs++;
return 1;
}
@@ -908,6 +898,12 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
unsigned long gp_duration;
WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
+
+ /*
+ * Ensure that all grace-period and pre-grace-period activity
+ * is seen before the assignment to rsp->completed.
+ */
+ smp_mb(); /* See above block comment. */
gp_duration = jiffies - rsp->gp_start;
if (gp_duration > rsp->gp_max)
rsp->gp_max = gp_duration;
@@ -1455,25 +1451,11 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
*/
static void rcu_process_callbacks(void)
{
- /*
- * Memory references from any prior RCU read-side critical sections
- * executed by the interrupted code must be seen before any RCU
- * grace-period manipulations below.
- */
- smp_mb(); /* See above block comment. */
-
__rcu_process_callbacks(&rcu_sched_state,
&__get_cpu_var(rcu_sched_data));
__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
rcu_preempt_process_callbacks();
- /*
- * Memory references from any later RCU read-side critical sections
- * executed by the interrupted code must be seen after any RCU
- * grace-period manipulations above.
- */
- smp_mb(); /* See above block comment. */
-
/* If we are last CPU on way to dyntick-idle mode, accelerate it. */
rcu_needs_cpu_flush();
}