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Date: Fri, 10 Oct 2008 02:44:53 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
"Paul E. McKenney" <paulmck@...ibm.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [git pull] RCU updates for v2.6.28
Linus,
Please pull the latest rcu-v28-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git rcu-v28-for-linus
Thanks,
Ingo
------------------>
Harvey Harrison (1):
rcu: fix sparse shadowed variable warning
Hiroshi Shimamoto (2):
rcuclassic: fix compilation NG
rcuclassic: fix compiler warning
Ingo Molnar (2):
rcu, debug: detect stalled grace periods, cleanups
rcu: RCU-based detection of stalled CPUs for Classic RCU, fix
Lai Jiangshan (3):
rcu classic: simplify the next pending batch
rcu classic: new algorithm for callbacks-processing(v2)
doc/RCU: fix pseudocode in rcuref.txt
Mathieu Desnoyers (1):
rcu: add rcu_read_lock_sched() / rcu_read_unlock_sched()
Paul E. McKenney (10):
rcu, debug: detect stalled grace periods
rcu: prevent console flood when one CPU sees another AWOL via RCU
rcu: classic RCU locking and memory-barrier cleanups
rcu: fixes to include/linux/rcupreempt.h
rcu: remove list_for_each_rcu()
rcu: fix classic RCU locking cleanup lockdep problem
rcu: remove redundant ACCESS_ONCE definition from rcupreempt.c
rcu: fix locking cleanup fallout
rcu: use irq-safe locks
rcu: RCU-based detection of stalled CPUs for Classic RCU
Steven Rostedt (2):
rcu: just rename call_rcu_bh instead of making it a macro
rcu: trace fix possible mem-leak
Documentation/RCU/checklist.txt | 2 +-
Documentation/RCU/rcuref.txt | 16 +-
Documentation/RCU/whatisRCU.txt | 2 -
include/linux/compiler.h | 4 +-
include/linux/rcuclassic.h | 37 +++--
include/linux/rculist.h | 14 --
include/linux/rcupdate.h | 20 +++
include/linux/rcupreempt.h | 11 +-
kernel/rcuclassic.c | 337 +++++++++++++++++++++++++++++----------
kernel/rcupreempt.c | 8 -
kernel/rcupreempt_trace.c | 7 +-
lib/Kconfig.debug | 13 ++
12 files changed, 337 insertions(+), 134 deletions(-)
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index cf5562c..6e25340 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -210,7 +210,7 @@ over a rather long period of time, but improvements are always welcome!
number of updates per grace period.
9. All RCU list-traversal primitives, which include
- rcu_dereference(), list_for_each_rcu(), list_for_each_entry_rcu(),
+ rcu_dereference(), list_for_each_entry_rcu(),
list_for_each_continue_rcu(), and list_for_each_safe_rcu(),
must be either within an RCU read-side critical section or
must be protected by appropriate update-side locks. RCU
diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index 451de2a..4202ad0 100644
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -29,9 +29,9 @@ release_referenced() delete()
}
If this list/array is made lock free using RCU as in changing the
-write_lock() in add() and delete() to spin_lock and changing read_lock
-in search_and_reference to rcu_read_lock(), the atomic_get in
-search_and_reference could potentially hold reference to an element which
+write_lock() in add() and delete() to spin_lock() and changing read_lock()
+in search_and_reference() to rcu_read_lock(), the atomic_inc() in
+search_and_reference() could potentially hold reference to an element which
has already been deleted from the list/array. Use atomic_inc_not_zero()
in this scenario as follows:
@@ -40,20 +40,20 @@ add() search_and_reference()
{ {
alloc_object rcu_read_lock();
... search_for_element
- atomic_set(&el->rc, 1); if (atomic_inc_not_zero(&el->rc)) {
- write_lock(&list_lock); rcu_read_unlock();
+ atomic_set(&el->rc, 1); if (!atomic_inc_not_zero(&el->rc)) {
+ spin_lock(&list_lock); rcu_read_unlock();
return FAIL;
add_element }
... ...
- write_unlock(&list_lock); rcu_read_unlock();
+ spin_unlock(&list_lock); rcu_read_unlock();
} }
3. 4.
release_referenced() delete()
{ {
- ... write_lock(&list_lock);
+ ... spin_lock(&list_lock);
if (atomic_dec_and_test(&el->rc)) ...
call_rcu(&el->head, el_free); delete_element
- ... write_unlock(&list_lock);
+ ... spin_unlock(&list_lock);
} ...
if (atomic_dec_and_test(&el->rc))
call_rcu(&el->head, el_free);
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index e04d643..9617082 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -786,8 +786,6 @@ RCU pointer/list traversal:
list_for_each_entry_rcu
hlist_for_each_entry_rcu
- list_for_each_rcu (to be deprecated in favor of
- list_for_each_entry_rcu)
list_for_each_continue_rcu (to be deprecated in favor of new
list_for_each_entry_continue_rcu)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index c8bd2da..8322141 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -190,7 +190,9 @@ extern void __chk_io_ptr(const volatile void __iomem *);
* ACCESS_ONCE() in different C statements.
*
* This macro does absolutely -nothing- to prevent the CPU from reordering,
- * merging, or refetching absolutely anything at any time.
+ * merging, or refetching absolutely anything at any time. Its main intended
+ * use is to mediate communication between process-level code and irq/NMI
+ * handlers, all running on the same CPU.
*/
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
index 4ab8436..5f89b62 100644
--- a/include/linux/rcuclassic.h
+++ b/include/linux/rcuclassic.h
@@ -40,12 +40,21 @@
#include <linux/cpumask.h>
#include <linux/seqlock.h>
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+#define RCU_SECONDS_TILL_STALL_CHECK ( 3 * HZ) /* for rcp->jiffies_stall */
+#define RCU_SECONDS_TILL_STALL_RECHECK (30 * HZ) /* for rcp->jiffies_stall */
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
/* Global control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
long cur; /* Current batch number. */
long completed; /* Number of the last completed batch */
- int next_pending; /* Is the next batch already waiting? */
+ long pending; /* Number of the last pending batch */
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+ unsigned long gp_start; /* Time at which GP started in jiffies. */
+ unsigned long jiffies_stall;
+ /* Time at which to check for CPU stalls. */
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
int signaled;
@@ -66,11 +75,7 @@ static inline int rcu_batch_after(long a, long b)
return (a - b) > 0;
}
-/*
- * Per-CPU data for Read-Copy UPdate.
- * nxtlist - new callbacks are added here
- * curlist - current batch for which quiescent cycle started if any
- */
+/* Per-CPU data for Read-Copy UPdate. */
struct rcu_data {
/* 1) quiescent state handling : */
long quiescbatch; /* Batch # for grace period */
@@ -78,12 +83,24 @@ struct rcu_data {
int qs_pending; /* core waits for quiesc state */
/* 2) batch handling */
- long batch; /* Batch # for current RCU batch */
+ /*
+ * if nxtlist is not NULL, then:
+ * batch:
+ * The batch # for the last entry of nxtlist
+ * [*nxttail[1], NULL = *nxttail[2]):
+ * Entries that batch # <= batch
+ * [*nxttail[0], *nxttail[1]):
+ * Entries that batch # <= batch - 1
+ * [nxtlist, *nxttail[0]):
+ * Entries that batch # <= batch - 2
+ * The grace period for these entries has completed, and
+ * the other grace-period-completed entries may be moved
+ * here temporarily in rcu_process_callbacks().
+ */
+ long batch;
struct rcu_head *nxtlist;
- struct rcu_head **nxttail;
+ struct rcu_head **nxttail[3];
long qlen; /* # of queued callbacks */
- struct rcu_head *curlist;
- struct rcu_head **curtail;
struct rcu_head *donelist;
struct rcu_head **donetail;
long blimit; /* Upper limit on a processed batch */
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index eb4443c..e649bd3 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -198,20 +198,6 @@ static inline void list_splice_init_rcu(struct list_head *list,
at->prev = last;
}
-/**
- * list_for_each_rcu - iterate over an rcu-protected list
- * @pos: the &struct list_head to use as a loop cursor.
- * @head: the head for your list.
- *
- * This list-traversal primitive may safely run concurrently with
- * the _rcu list-mutation primitives such as list_add_rcu()
- * as long as the traversal is guarded by rcu_read_lock().
- */
-#define list_for_each_rcu(pos, head) \
- for (pos = rcu_dereference((head)->next); \
- prefetch(pos->next), pos != (head); \
- pos = rcu_dereference(pos->next))
-
#define __list_for_each_rcu(pos, head) \
for (pos = rcu_dereference((head)->next); \
pos != (head); \
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index e8b4039..86f1f5e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -133,6 +133,26 @@ struct rcu_head {
#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
/**
+ * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
+ *
+ * Should be used with either
+ * - synchronize_sched()
+ * or
+ * - call_rcu_sched() and rcu_barrier_sched()
+ * on the write-side to insure proper synchronization.
+ */
+#define rcu_read_lock_sched() preempt_disable()
+
+/*
+ * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
+ *
+ * See rcu_read_lock_sched for more information.
+ */
+#define rcu_read_unlock_sched() preempt_enable()
+
+
+
+/**
* rcu_dereference - fetch an RCU-protected pointer in an
* RCU read-side critical section. This pointer may later
* be safely dereferenced.
diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h
index 0967f03..3e05c09 100644
--- a/include/linux/rcupreempt.h
+++ b/include/linux/rcupreempt.h
@@ -57,7 +57,13 @@ static inline void rcu_qsctr_inc(int cpu)
rdssp->sched_qs++;
}
#define rcu_bh_qsctr_inc(cpu)
-#define call_rcu_bh(head, rcu) call_rcu(head, rcu)
+
+/*
+ * Someone might want to pass call_rcu_bh as a function pointer.
+ * So this needs to just be a rename and not a macro function.
+ * (no parentheses)
+ */
+#define call_rcu_bh call_rcu
/**
* call_rcu_sched - Queue RCU callback for invocation after sched grace period.
@@ -111,7 +117,6 @@ extern struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu);
struct softirq_action;
#ifdef CONFIG_NO_HZ
-DECLARE_PER_CPU(struct rcu_dyntick_sched, rcu_dyntick_sched);
static inline void rcu_enter_nohz(void)
{
@@ -126,8 +131,8 @@ static inline void rcu_exit_nohz(void)
{
static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
- smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
__get_cpu_var(rcu_dyntick_sched).dynticks++;
+ smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
WARN_ON_RATELIMIT(!(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1),
&rs);
}
diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index aad93cd..37f72e5 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -47,6 +47,7 @@
#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;
@@ -60,12 +61,14 @@ EXPORT_SYMBOL_GPL(rcu_lock_map);
static struct rcu_ctrlblk rcu_ctrlblk = {
.cur = -300,
.completed = -300,
+ .pending = -300,
.lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
.cpumask = CPU_MASK_NONE,
};
static struct rcu_ctrlblk rcu_bh_ctrlblk = {
.cur = -300,
.completed = -300,
+ .pending = -300,
.lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
.cpumask = CPU_MASK_NONE,
};
@@ -83,7 +86,10 @@ static void force_quiescent_state(struct rcu_data *rdp,
{
int cpu;
cpumask_t cpumask;
+ unsigned long flags;
+
set_need_resched();
+ spin_lock_irqsave(&rcp->lock, flags);
if (unlikely(!rcp->signaled)) {
rcp->signaled = 1;
/*
@@ -109,6 +115,7 @@ static void force_quiescent_state(struct rcu_data *rdp,
for_each_cpu_mask_nr(cpu, cpumask)
smp_send_reschedule(cpu);
}
+ spin_unlock_irqrestore(&rcp->lock, flags);
}
#else
static inline void force_quiescent_state(struct rcu_data *rdp,
@@ -118,6 +125,126 @@ static inline void force_quiescent_state(struct rcu_data *rdp,
}
#endif
+static void __call_rcu(struct rcu_head *head, struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ long batch;
+
+ head->next = NULL;
+ smp_mb(); /* Read of rcu->cur must happen after any change by caller. */
+
+ /*
+ * Determine the batch number of this callback.
+ *
+ * Using ACCESS_ONCE to avoid the following error when gcc eliminates
+ * local variable "batch" and emits codes like this:
+ * 1) rdp->batch = rcp->cur + 1 # gets old value
+ * ......
+ * 2)rcu_batch_after(rcp->cur + 1, rdp->batch) # gets new value
+ * then [*nxttail[0], *nxttail[1]) may contain callbacks
+ * that batch# = rdp->batch, see the comment of struct rcu_data.
+ */
+ batch = ACCESS_ONCE(rcp->cur) + 1;
+
+ if (rdp->nxtlist && rcu_batch_after(batch, rdp->batch)) {
+ /* process callbacks */
+ rdp->nxttail[0] = rdp->nxttail[1];
+ rdp->nxttail[1] = rdp->nxttail[2];
+ if (rcu_batch_after(batch - 1, rdp->batch))
+ rdp->nxttail[0] = rdp->nxttail[2];
+ }
+
+ rdp->batch = batch;
+ *rdp->nxttail[2] = head;
+ rdp->nxttail[2] = &head->next;
+
+ if (unlikely(++rdp->qlen > qhimark)) {
+ rdp->blimit = INT_MAX;
+ force_quiescent_state(rdp, &rcu_ctrlblk);
+ }
+}
+
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+
+static void record_gp_stall_check_time(struct rcu_ctrlblk *rcp)
+{
+ rcp->gp_start = jiffies;
+ rcp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
+}
+
+static void print_other_cpu_stall(struct rcu_ctrlblk *rcp)
+{
+ int cpu;
+ long delta;
+ unsigned long flags;
+
+ /* Only let one CPU complain about others per time interval. */
+
+ spin_lock_irqsave(&rcp->lock, flags);
+ delta = jiffies - rcp->jiffies_stall;
+ if (delta < 2 || rcp->cur != rcp->completed) {
+ spin_unlock_irqrestore(&rcp->lock, flags);
+ return;
+ }
+ rcp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
+ spin_unlock_irqrestore(&rcp->lock, flags);
+
+ /* OK, time to rat on our buddy... */
+
+ printk(KERN_ERR "RCU detected CPU stalls:");
+ for_each_possible_cpu(cpu) {
+ if (cpu_isset(cpu, rcp->cpumask))
+ printk(" %d", cpu);
+ }
+ printk(" (detected by %d, t=%ld jiffies)\n",
+ smp_processor_id(), (long)(jiffies - rcp->gp_start));
+}
+
+static void print_cpu_stall(struct rcu_ctrlblk *rcp)
+{
+ unsigned long flags;
+
+ printk(KERN_ERR "RCU detected CPU %d stall (t=%lu/%lu jiffies)\n",
+ smp_processor_id(), jiffies,
+ jiffies - rcp->gp_start);
+ dump_stack();
+ spin_lock_irqsave(&rcp->lock, flags);
+ if ((long)(jiffies - rcp->jiffies_stall) >= 0)
+ rcp->jiffies_stall =
+ jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
+ spin_unlock_irqrestore(&rcp->lock, flags);
+ set_need_resched(); /* kick ourselves to get things going. */
+}
+
+static void check_cpu_stall(struct rcu_ctrlblk *rcp)
+{
+ long delta;
+
+ delta = jiffies - rcp->jiffies_stall;
+ if (cpu_isset(smp_processor_id(), rcp->cpumask) && delta >= 0) {
+
+ /* We haven't checked in, so go dump stack. */
+ print_cpu_stall(rcp);
+
+ } else if (rcp->cur != rcp->completed && delta >= 2) {
+
+ /* They had two seconds to dump stack, so complain. */
+ print_other_cpu_stall(rcp);
+ }
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+
+static void record_gp_stall_check_time(struct rcu_ctrlblk *rcp)
+{
+}
+
+static inline void check_cpu_stall(struct rcu_ctrlblk *rcp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+
/**
* call_rcu - Queue an RCU callback for invocation after a grace period.
* @head: structure to be used for queueing the RCU updates.
@@ -133,18 +260,10 @@ 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 = &__get_cpu_var(rcu_data);
- *rdp->nxttail = head;
- rdp->nxttail = &head->next;
- if (unlikely(++rdp->qlen > qhimark)) {
- rdp->blimit = INT_MAX;
- force_quiescent_state(rdp, &rcu_ctrlblk);
- }
+ __call_rcu(head, &rcu_ctrlblk, &__get_cpu_var(rcu_data));
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(call_rcu);
@@ -169,20 +288,10 @@ void call_rcu_bh(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 = &__get_cpu_var(rcu_bh_data);
- *rdp->nxttail = head;
- rdp->nxttail = &head->next;
-
- if (unlikely(++rdp->qlen > qhimark)) {
- rdp->blimit = INT_MAX;
- force_quiescent_state(rdp, &rcu_bh_ctrlblk);
- }
-
+ __call_rcu(head, &rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
@@ -211,12 +320,6 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
static inline void raise_rcu_softirq(void)
{
raise_softirq(RCU_SOFTIRQ);
- /*
- * The smp_mb() here is required to ensure that this cpu's
- * __rcu_process_callbacks() reads the most recently updated
- * value of rcu->cur.
- */
- smp_mb();
}
/*
@@ -225,6 +328,7 @@ static inline void raise_rcu_softirq(void)
*/
static void rcu_do_batch(struct rcu_data *rdp)
{
+ unsigned long flags;
struct rcu_head *next, *list;
int count = 0;
@@ -239,9 +343,9 @@ static void rcu_do_batch(struct rcu_data *rdp)
}
rdp->donelist = list;
- local_irq_disable();
+ local_irq_save(flags);
rdp->qlen -= count;
- local_irq_enable();
+ local_irq_restore(flags);
if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
rdp->blimit = blimit;
@@ -269,6 +373,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
* rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
* period (if necessary).
*/
+
/*
* Register a new batch of callbacks, and start it up if there is currently no
* active batch and the batch to be registered has not already occurred.
@@ -276,15 +381,10 @@ static void rcu_do_batch(struct rcu_data *rdp)
*/
static void rcu_start_batch(struct rcu_ctrlblk *rcp)
{
- if (rcp->next_pending &&
+ if (rcp->cur != rcp->pending &&
rcp->completed == rcp->cur) {
- rcp->next_pending = 0;
- /*
- * next_pending == 0 must be visible in
- * __rcu_process_callbacks() before it can see new value of cur.
- */
- smp_wmb();
rcp->cur++;
+ record_gp_stall_check_time(rcp);
/*
* Accessing nohz_cpu_mask before incrementing rcp->cur needs a
@@ -322,6 +422,8 @@ static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
struct rcu_data *rdp)
{
+ unsigned long flags;
+
if (rdp->quiescbatch != rcp->cur) {
/* start new grace period: */
rdp->qs_pending = 1;
@@ -345,7 +447,7 @@ static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
return;
rdp->qs_pending = 0;
- spin_lock(&rcp->lock);
+ spin_lock_irqsave(&rcp->lock, flags);
/*
* rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
* during cpu startup. Ignore the quiescent state.
@@ -353,7 +455,7 @@ static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
if (likely(rdp->quiescbatch == rcp->cur))
cpu_quiet(rdp->cpu, rcp);
- spin_unlock(&rcp->lock);
+ spin_unlock_irqrestore(&rcp->lock, flags);
}
@@ -364,33 +466,38 @@ static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
* which is dead and hence not processing interrupts.
*/
static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
- struct rcu_head **tail)
+ struct rcu_head **tail, long batch)
{
- local_irq_disable();
- *this_rdp->nxttail = list;
- if (list)
- this_rdp->nxttail = tail;
- local_irq_enable();
+ unsigned long flags;
+
+ if (list) {
+ local_irq_save(flags);
+ this_rdp->batch = batch;
+ *this_rdp->nxttail[2] = list;
+ this_rdp->nxttail[2] = tail;
+ local_irq_restore(flags);
+ }
}
static void __rcu_offline_cpu(struct rcu_data *this_rdp,
struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
{
- /* if the cpu going offline owns the grace period
+ unsigned long flags;
+
+ /*
+ * if the cpu going offline owns the grace period
* we can block indefinitely waiting for it, so flush
* it here
*/
- spin_lock_bh(&rcp->lock);
+ spin_lock_irqsave(&rcp->lock, flags);
if (rcp->cur != rcp->completed)
cpu_quiet(rdp->cpu, rcp);
- spin_unlock_bh(&rcp->lock);
- rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
- rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
- rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
+ rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail, rcp->cur + 1);
+ rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail[2], rcp->cur + 1);
+ spin_unlock(&rcp->lock);
- local_irq_disable();
this_rdp->qlen += rdp->qlen;
- local_irq_enable();
+ local_irq_restore(flags);
}
static void rcu_offline_cpu(int cpu)
@@ -420,38 +527,52 @@ static void rcu_offline_cpu(int cpu)
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
struct rcu_data *rdp)
{
- if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
- *rdp->donetail = rdp->curlist;
- rdp->donetail = rdp->curtail;
- rdp->curlist = NULL;
- rdp->curtail = &rdp->curlist;
- }
+ unsigned long flags;
+ long completed_snap;
- if (rdp->nxtlist && !rdp->curlist) {
- local_irq_disable();
- rdp->curlist = rdp->nxtlist;
- rdp->curtail = rdp->nxttail;
- rdp->nxtlist = NULL;
- rdp->nxttail = &rdp->nxtlist;
- local_irq_enable();
+ if (rdp->nxtlist) {
+ local_irq_save(flags);
+ completed_snap = ACCESS_ONCE(rcp->completed);
/*
- * start the next batch of callbacks
+ * move the other grace-period-completed entries to
+ * [rdp->nxtlist, *rdp->nxttail[0]) temporarily
*/
+ if (!rcu_batch_before(completed_snap, rdp->batch))
+ rdp->nxttail[0] = rdp->nxttail[1] = rdp->nxttail[2];
+ else if (!rcu_batch_before(completed_snap, rdp->batch - 1))
+ rdp->nxttail[0] = rdp->nxttail[1];
- /* determine batch number */
- rdp->batch = rcp->cur + 1;
- /* see the comment and corresponding wmb() in
- * the rcu_start_batch()
+ /*
+ * the grace period for entries in
+ * [rdp->nxtlist, *rdp->nxttail[0]) has completed and
+ * move these entries to donelist
*/
- smp_rmb();
+ if (rdp->nxttail[0] != &rdp->nxtlist) {
+ *rdp->donetail = rdp->nxtlist;
+ rdp->donetail = rdp->nxttail[0];
+ rdp->nxtlist = *rdp->nxttail[0];
+ *rdp->donetail = NULL;
+
+ if (rdp->nxttail[1] == rdp->nxttail[0])
+ rdp->nxttail[1] = &rdp->nxtlist;
+ if (rdp->nxttail[2] == rdp->nxttail[0])
+ rdp->nxttail[2] = &rdp->nxtlist;
+ rdp->nxttail[0] = &rdp->nxtlist;
+ }
+
+ local_irq_restore(flags);
+
+ if (rcu_batch_after(rdp->batch, rcp->pending)) {
+ unsigned long flags2;
- if (!rcp->next_pending) {
/* and start it/schedule start if it's a new batch */
- spin_lock(&rcp->lock);
- rcp->next_pending = 1;
- rcu_start_batch(rcp);
- spin_unlock(&rcp->lock);
+ spin_lock_irqsave(&rcp->lock, flags2);
+ if (rcu_batch_after(rdp->batch, rcp->pending)) {
+ rcp->pending = rdp->batch;
+ rcu_start_batch(rcp);
+ }
+ spin_unlock_irqrestore(&rcp->lock, flags2);
}
}
@@ -462,21 +583,53 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
static void rcu_process_callbacks(struct softirq_action *unused)
{
+ /*
+ * Memory references from any prior RCU read-side critical sections
+ * executed by the interrupted code must be see before any RCU
+ * grace-period manupulations below.
+ */
+
+ smp_mb(); /* See above block comment. */
+
__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
+
+ /*
+ * Memory references from any later RCU read-side critical sections
+ * executed by the interrupted code must be see after any RCU
+ * grace-period manupulations above.
+ */
+
+ smp_mb(); /* See above block comment. */
}
static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
{
- /* This cpu has pending rcu entries and the grace period
- * for them has completed.
- */
- if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
- return 1;
+ /* Check for CPU stalls, if enabled. */
+ check_cpu_stall(rcp);
- /* This cpu has no pending entries, but there are new entries */
- if (!rdp->curlist && rdp->nxtlist)
- return 1;
+ if (rdp->nxtlist) {
+ long completed_snap = ACCESS_ONCE(rcp->completed);
+
+ /*
+ * This cpu has pending rcu entries and the grace period
+ * for them has completed.
+ */
+ if (!rcu_batch_before(completed_snap, rdp->batch))
+ return 1;
+ if (!rcu_batch_before(completed_snap, rdp->batch - 1) &&
+ rdp->nxttail[0] != rdp->nxttail[1])
+ return 1;
+ if (rdp->nxttail[0] != &rdp->nxtlist)
+ return 1;
+
+ /*
+ * This cpu has pending rcu entries and the new batch
+ * for then hasn't been started nor scheduled start
+ */
+ if (rcu_batch_after(rdp->batch, rcp->pending))
+ return 1;
+ }
/* This cpu has finished callbacks to invoke */
if (rdp->donelist)
@@ -512,9 +665,15 @@ int rcu_needs_cpu(int cpu)
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
- return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
+ return !!rdp->nxtlist || !!rdp_bh->nxtlist || rcu_pending(cpu);
}
+/*
+ * 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.
+ */
void rcu_check_callbacks(int cpu, int user)
{
if (user ||
@@ -558,14 +717,17 @@ void rcu_check_callbacks(int cpu, int user)
static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
struct rcu_data *rdp)
{
+ unsigned long flags;
+
+ spin_lock_irqsave(&rcp->lock, flags);
memset(rdp, 0, sizeof(*rdp));
- rdp->curtail = &rdp->curlist;
- rdp->nxttail = &rdp->nxtlist;
+ rdp->nxttail[0] = rdp->nxttail[1] = rdp->nxttail[2] = &rdp->nxtlist;
rdp->donetail = &rdp->donelist;
rdp->quiescbatch = rcp->completed;
rdp->qs_pending = 0;
rdp->cpu = cpu;
rdp->blimit = blimit;
+ spin_unlock_irqrestore(&rcp->lock, flags);
}
static void __cpuinit rcu_online_cpu(int cpu)
@@ -610,6 +772,9 @@ static struct notifier_block __cpuinitdata rcu_nb = {
*/
void __init __rcu_init(void)
{
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+ printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
(void *)(long)smp_processor_id());
/* Register notifier for non-boot CPUs */
diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
index 2782793..ca4bbbe 100644
--- a/kernel/rcupreempt.c
+++ b/kernel/rcupreempt.c
@@ -59,14 +59,6 @@
#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.
*/
diff --git a/kernel/rcupreempt_trace.c b/kernel/rcupreempt_trace.c
index 5edf82c..35c2d33 100644
--- a/kernel/rcupreempt_trace.c
+++ b/kernel/rcupreempt_trace.c
@@ -308,11 +308,16 @@ out:
static int __init rcupreempt_trace_init(void)
{
+ int ret;
+
mutex_init(&rcupreempt_trace_mutex);
rcupreempt_trace_buf = kmalloc(RCUPREEMPT_TRACE_BUF_SIZE, GFP_KERNEL);
if (!rcupreempt_trace_buf)
return 1;
- return rcupreempt_debugfs_init();
+ ret = rcupreempt_debugfs_init();
+ if (ret)
+ kfree(rcupreempt_trace_buf);
+ return ret;
}
static void __exit rcupreempt_trace_cleanup(void)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 0b50481..9fee969 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -597,6 +597,19 @@ config RCU_TORTURE_TEST_RUNNABLE
Say N here if you want the RCU torture tests to start only
after being manually enabled via /proc.
+config RCU_CPU_STALL_DETECTOR
+ bool "Check for stalled CPUs delaying RCU grace periods"
+ depends on CLASSIC_RCU
+ default n
+ help
+ This option causes RCU to printk information on which
+ CPUs are delaying the current grace period, but only when
+ the grace period extends for excessive time periods.
+
+ Say Y if you want RCU to perform such checks.
+
+ Say N if you are unsure.
+
config KPROBES_SANITY_TEST
bool "Kprobes sanity tests"
depends on DEBUG_KERNEL
--
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