when publicizing a pointer to a structure that can
be traversed by an RCU read-side critical section.
-5. If call_rcu(), or a related primitive such as call_rcu_bh() or
- call_rcu_sched(), is used, the callback function must be
- written to be called from softirq context. In particular,
+5. If call_rcu(), or a related primitive such as call_rcu_bh(),
+ call_rcu_sched(), or call_srcu() is used, the callback function
+ must be written to be called from softirq context. In particular,
it cannot block.
6. Since synchronize_rcu() can block, it cannot be called from
updater uses call_rcu_sched() or synchronize_sched(), then
the corresponding readers must disable preemption, possibly
by calling rcu_read_lock_sched() and rcu_read_unlock_sched().
- If the updater uses synchronize_srcu(), the the corresponding
- readers must use srcu_read_lock() and srcu_read_unlock(),
- and with the same srcu_struct. The rules for the expedited
- primitives are the same as for their non-expedited counterparts.
- Mixing things up will result in confusion and broken kernels.
+ If the updater uses synchronize_srcu() or call_srcu(),
+ the the corresponding readers must use srcu_read_lock() and
+ srcu_read_unlock(), and with the same srcu_struct. The rules for
+ the expedited primitives are the same as for their non-expedited
+ counterparts. Mixing things up will result in confusion and
+ broken kernels.
One exception to this rule: rcu_read_lock() and rcu_read_unlock()
may be substituted for rcu_read_lock_bh() and rcu_read_unlock_bh()
victim CPU from ever going offline.)
14. SRCU (srcu_read_lock(), srcu_read_unlock(), srcu_dereference(),
- synchronize_srcu(), and synchronize_srcu_expedited()) may only
- be invoked from process context. Unlike other forms of RCU, it
- -is- permissible to block in an SRCU read-side critical section
- (demarked by srcu_read_lock() and srcu_read_unlock()), hence the
- "SRCU": "sleepable RCU". Please note that if you don't need
- to sleep in read-side critical sections, you should be using
- RCU rather than SRCU, because RCU is almost always faster and
- easier to use than is SRCU.
+ synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu())
+ may only be invoked from process context. Unlike other forms of
+ RCU, it -is- permissible to block in an SRCU read-side critical
+ section (demarked by srcu_read_lock() and srcu_read_unlock()),
+ hence the "SRCU": "sleepable RCU". Please note that if you
+ don't need to sleep in read-side critical sections, you should be
+ using RCU rather than SRCU, because RCU is almost always faster
+ and easier to use than is SRCU.
If you need to enter your read-side critical section in a
hardirq or exception handler, and then exit that same read-side
cleanup_srcu_struct(). These are passed a "struct srcu_struct"
that defines the scope of a given SRCU domain. Once initialized,
the srcu_struct is passed to srcu_read_lock(), srcu_read_unlock()
- synchronize_srcu(), and synchronize_srcu_expedited(). A given
- synchronize_srcu() waits only for SRCU read-side critical
+ synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu().
+ A given synchronize_srcu() waits only for SRCU read-side critical
sections governed by srcu_read_lock() and srcu_read_unlock()
calls that have been passed the same srcu_struct. This property
is what makes sleeping read-side critical sections tolerable --
requiring SRCU's read-side deadlock immunity or low read-side
realtime latency.
- Note that, rcu_assign_pointer() relates to SRCU just as they do
+ Note that, rcu_assign_pointer() relates to SRCU just as it does
to other forms of RCU.
15. The whole point of call_rcu(), synchronize_rcu(), and friends
2. Execute rcu_barrier().
3. Allow the module to be unloaded.
-Quick Quiz #1: Why is there no srcu_barrier()?
-
The rcutorture module makes use of rcu_barrier in its exit function
as follows:
Then lines 55-62 print status and do operation-specific cleanup, and
then return, permitting the module-unload operation to be completed.
-Quick Quiz #2: Is there any other situation where rcu_barrier() might
+Quick Quiz #1: Is there any other situation where rcu_barrier() might
be required?
Your module might have additional complications. For example, if your
4 complete(&rcu_barrier_completion);
5 }
-Quick Quiz #3: What happens if CPU 0's rcu_barrier_func() executes
+Quick Quiz #2: What happens if CPU 0's rcu_barrier_func() executes
immediately (thus incrementing rcu_barrier_cpu_count to the
value one), but the other CPU's rcu_barrier_func() invocations
are delayed for a full grace period? Couldn't this result in
Answers to Quick Quizzes
-Quick Quiz #1: Why is there no srcu_barrier()?
-
-Answer: Since there is no call_srcu(), there can be no outstanding SRCU
- callbacks. Therefore, there is no need to wait for them.
-
-Quick Quiz #2: Is there any other situation where rcu_barrier() might
+Quick Quiz #1: Is there any other situation where rcu_barrier() might
be required?
Answer: Interestingly enough, rcu_barrier() was not originally
implementing rcutorture, and found that rcu_barrier() solves
this problem as well.
-Quick Quiz #3: What happens if CPU 0's rcu_barrier_func() executes
+Quick Quiz #2: What happens if CPU 0's rcu_barrier_func() executes
immediately (thus incrementing rcu_barrier_cpu_count to the
value one), but the other CPU's rcu_barrier_func() invocations
are delayed for a full grace period? Couldn't this result in
and synchronize_rcu_bh_expedited().
"srcu": srcu_read_lock(), srcu_read_unlock() and
+ call_srcu().
+
+ "srcu_sync": srcu_read_lock(), srcu_read_unlock() and
synchronize_srcu().
"srcu_expedited": srcu_read_lock(), srcu_read_unlock() and
synchronize_srcu_expedited().
+ "srcu_raw": srcu_read_lock_raw(), srcu_read_unlock_raw(),
+ and call_srcu().
+
+ "srcu_raw_sync": srcu_read_lock_raw(), srcu_read_unlock_raw(),
+ and synchronize_srcu().
+
"sched": preempt_disable(), preempt_enable(), and
call_rcu_sched().
SRCU: Critical sections Grace period Barrier
- srcu_read_lock synchronize_srcu N/A
- srcu_read_unlock synchronize_srcu_expedited
- srcu_read_lock_raw
+ srcu_read_lock synchronize_srcu srcu_barrier
+ srcu_read_unlock call_srcu
+ srcu_read_lock_raw synchronize_srcu_expedited
srcu_read_unlock_raw
srcu_dereference
.children = LIST_HEAD_INIT(tsk.children), \
.sibling = LIST_HEAD_INIT(tsk.sibling), \
.group_leader = &tsk, \
- RCU_INIT_POINTER(.real_cred, &init_cred), \
- RCU_INIT_POINTER(.cred, &init_cred), \
+ RCU_POINTER_INITIALIZER(real_cred, &init_cred), \
+ RCU_POINTER_INITIALIZER(cred, &init_cred), \
.comm = INIT_TASK_COMM, \
.thread = INIT_THREAD, \
.fs = &init_fs, \
rwsem_is_locked(&((struct key *)(KEY))->sem)))
#define rcu_assign_keypointer(KEY, PAYLOAD) \
- (rcu_assign_pointer((KEY)->payload.rcudata, PAYLOAD))
+do { \
+ rcu_assign_pointer((KEY)->payload.rcudata, (PAYLOAD)); \
+} while (0)
#ifdef CONFIG_SYSCTL
extern ctl_table key_sysctls[];
extern void __rcu_read_lock(void);
extern void __rcu_read_unlock(void);
+extern void rcu_read_unlock_special(struct task_struct *t);
void synchronize_rcu(void);
/*
}
#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP)
+extern int rcu_is_cpu_idle(void);
+#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */
+
#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
bool rcu_lockdep_current_cpu_online(void);
#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
-#ifdef CONFIG_PROVE_RCU
-extern int rcu_is_cpu_idle(void);
-#else /* !CONFIG_PROVE_RCU */
-static inline int rcu_is_cpu_idle(void)
-{
- return 0;
-}
-#endif /* else !CONFIG_PROVE_RCU */
-
static inline void rcu_lock_acquire(struct lockdep_map *map)
{
lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_);
(_________p1); \
})
#define __rcu_assign_pointer(p, v, space) \
- ({ \
+ do { \
smp_wmb(); \
(p) = (typeof(*v) __force space *)(v); \
- })
+ } while (0)
/**
*
* Assigns the specified value to the specified RCU-protected
* pointer, ensuring that any concurrent RCU readers will see
- * any prior initialization. Returns the value assigned.
+ * any prior initialization.
*
* Inserts memory barriers on architectures that require them
* (which is most of them), and also prevents the compiler from
* the reader-accessible portions of the linked structure.
*/
#define RCU_INIT_POINTER(p, v) \
- p = (typeof(*v) __force __rcu *)(v)
-
-static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
-{
- return offset < 4096;
-}
-
-static __always_inline
-void __kfree_rcu(struct rcu_head *head, unsigned long offset)
-{
- typedef void (*rcu_callback)(struct rcu_head *);
-
- BUILD_BUG_ON(!__builtin_constant_p(offset));
-
- /* See the kfree_rcu() header comment. */
- BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));
+ do { \
+ p = (typeof(*v) __force __rcu *)(v); \
+ } while (0)
- kfree_call_rcu(head, (rcu_callback)offset);
-}
+/**
+ * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
+ *
+ * GCC-style initialization for an RCU-protected pointer in a structure field.
+ */
+#define RCU_POINTER_INITIALIZER(p, v) \
+ .p = (typeof(*v) __force __rcu *)(v)
/*
* Does the specified offset indicate that the corresponding rcu_head
#define __kfree_rcu(head, offset) \
do { \
BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
- call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
+ kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
} while (0)
/**
#ifdef CONFIG_PREEMPT_RCU
+/*
+ * Preemptible RCU implementation for rcu_read_lock().
+ * Just increment ->rcu_read_lock_nesting, shared state will be updated
+ * if we block.
+ */
+void __rcu_read_lock(void)
+{
+ current->rcu_read_lock_nesting++;
+ barrier(); /* critical section after entry code. */
+}
+EXPORT_SYMBOL_GPL(__rcu_read_lock);
+
+/*
+ * Preemptible RCU implementation for rcu_read_unlock().
+ * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
+ * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
+ * invoke rcu_read_unlock_special() to clean up after a context switch
+ * in an RCU read-side critical section and other special cases.
+ */
+void __rcu_read_unlock(void)
+{
+ struct task_struct *t = current;
+
+ if (t->rcu_read_lock_nesting != 1) {
+ --t->rcu_read_lock_nesting;
+ } else {
+ barrier(); /* critical section before exit code. */
+ t->rcu_read_lock_nesting = INT_MIN;
+ barrier(); /* assign before ->rcu_read_unlock_special load */
+ if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
+ rcu_read_unlock_special(t);
+ barrier(); /* ->rcu_read_unlock_special load before assign */
+ t->rcu_read_lock_nesting = 0;
+ }
+#ifdef CONFIG_PROVE_LOCKING
+ {
+ int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
+
+ WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+ }
+#endif /* #ifdef CONFIG_PROVE_LOCKING */
+}
+EXPORT_SYMBOL_GPL(__rcu_read_unlock);
+
/*
* Check for a task exiting while in a preemptible-RCU read-side
* critical section, clean up if so. No need to issue warnings,
local_irq_restore(flags);
}
-#ifdef CONFIG_PROVE_RCU
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
/*
* Test whether RCU thinks that the current CPU is idle.
}
EXPORT_SYMBOL(rcu_is_cpu_idle);
-#endif /* #ifdef CONFIG_PROVE_RCU */
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/*
* Test whether the current CPU was interrupted from idle. Nested
RCU_TRACE(.rcb.name = "rcu_preempt")
};
-static void rcu_read_unlock_special(struct task_struct *t);
static int rcu_preempted_readers_exp(void);
static void rcu_report_exp_done(void);
local_irq_restore(flags);
}
-/*
- * Tiny-preemptible RCU implementation for rcu_read_lock().
- * Just increment ->rcu_read_lock_nesting, shared state will be updated
- * if we block.
- */
-void __rcu_read_lock(void)
-{
- current->rcu_read_lock_nesting++;
- barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */
-}
-EXPORT_SYMBOL_GPL(__rcu_read_lock);
-
/*
* Handle special cases during rcu_read_unlock(), such as needing to
* notify RCU core processing or task having blocked during the RCU
* read-side critical section.
*/
-static noinline void rcu_read_unlock_special(struct task_struct *t)
+void rcu_read_unlock_special(struct task_struct *t)
{
int empty;
int empty_exp;
local_irq_restore(flags);
}
-/*
- * Tiny-preemptible RCU implementation for rcu_read_unlock().
- * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
- * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
- * invoke rcu_read_unlock_special() to clean up after a context switch
- * in an RCU read-side critical section and other special cases.
- */
-void __rcu_read_unlock(void)
-{
- struct task_struct *t = current;
-
- barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */
- if (t->rcu_read_lock_nesting != 1)
- --t->rcu_read_lock_nesting;
- else {
- t->rcu_read_lock_nesting = INT_MIN;
- barrier(); /* assign before ->rcu_read_unlock_special load */
- if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
- rcu_read_unlock_special(t);
- barrier(); /* ->rcu_read_unlock_special load before assign */
- t->rcu_read_lock_nesting = 0;
- }
-#ifdef CONFIG_PROVE_LOCKING
- {
- int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
-
- WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
- }
-#endif /* #ifdef CONFIG_PROVE_LOCKING */
-}
-EXPORT_SYMBOL_GPL(__rcu_read_unlock);
-
/*
* Check for a quiescent state from the current CPU. When a task blocks,
* the task is recorded in the rcu_preempt_ctrlblk structure, which is
*/
int rcu_preempt_needs_cpu(void)
{
- if (!rcu_preempt_running_reader())
- rcu_preempt_cpu_qs();
return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
}
DEFINE_MUTEX(boost_mutex); /* protect setting boost_starttime */
/* and boost task create/destroy. */
static atomic_t barrier_cbs_count; /* Barrier callbacks registered. */
+static bool barrier_phase; /* Test phase. */
static atomic_t barrier_cbs_invoked; /* Barrier callbacks invoked. */
static wait_queue_head_t *barrier_cbs_wq; /* Coordinate barrier testing. */
static DECLARE_WAIT_QUEUE_HEAD(barrier_wq);
synchronize_srcu(&srcu_ctl);
}
+static void srcu_torture_call(struct rcu_head *head,
+ void (*func)(struct rcu_head *head))
+{
+ call_srcu(&srcu_ctl, head, func);
+}
+
+static void srcu_torture_barrier(void)
+{
+ srcu_barrier(&srcu_ctl);
+}
+
static int srcu_torture_stats(char *page)
{
int cnt = 0;
.completed = srcu_torture_completed,
.deferred_free = srcu_torture_deferred_free,
.sync = srcu_torture_synchronize,
- .call = NULL,
- .cb_barrier = NULL,
+ .call = srcu_torture_call,
+ .cb_barrier = srcu_torture_barrier,
.stats = srcu_torture_stats,
.name = "srcu"
};
do {
schedule_timeout_uninterruptible(1 + rcu_random(&rand)%10);
udelay(rcu_random(&rand) & 0x3ff);
- cur_ops->sync();
+ if (cur_ops->cb_barrier != NULL &&
+ rcu_random(&rand) % (nfakewriters * 8) == 0)
+ cur_ops->cb_barrier();
+ else
+ cur_ops->sync();
rcu_stutter_wait("rcu_torture_fakewriter");
} while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
static int rcu_torture_barrier_cbs(void *arg)
{
long myid = (long)arg;
+ bool lastphase = 0;
struct rcu_head rcu;
init_rcu_head_on_stack(&rcu);
set_user_nice(current, 19);
do {
wait_event(barrier_cbs_wq[myid],
- atomic_read(&barrier_cbs_count) == n_barrier_cbs ||
+ barrier_phase != lastphase ||
kthread_should_stop() ||
fullstop != FULLSTOP_DONTSTOP);
+ lastphase = barrier_phase;
+ smp_mb(); /* ensure barrier_phase load before ->call(). */
if (kthread_should_stop() || fullstop != FULLSTOP_DONTSTOP)
break;
cur_ops->call(&rcu, rcu_torture_barrier_cbf);
do {
atomic_set(&barrier_cbs_invoked, 0);
atomic_set(&barrier_cbs_count, n_barrier_cbs);
- /* wake_up() path contains the required barriers. */
+ smp_mb(); /* Ensure barrier_phase after prior assignments. */
+ barrier_phase = !barrier_phase;
for (i = 0; i < n_barrier_cbs; i++)
wake_up(&barrier_cbs_wq[i]);
wait_event(barrier_wq,
schedule_timeout_interruptible(HZ / 10);
} while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
VERBOSE_PRINTK_STRING("rcu_torture_barrier task stopping");
- rcutorture_shutdown_absorb("rcu_torture_barrier_cbs");
+ rcutorture_shutdown_absorb("rcu_torture_barrier");
while (!kthread_should_stop())
schedule_timeout_interruptible(1);
return 0;
static struct rcu_torture_ops *torture_ops[] =
{ &rcu_ops, &rcu_sync_ops, &rcu_expedited_ops,
&rcu_bh_ops, &rcu_bh_sync_ops, &rcu_bh_expedited_ops,
- &srcu_ops, &srcu_sync_ops, &srcu_raw_ops,
- &srcu_raw_sync_ops, &srcu_expedited_ops,
+ &srcu_ops, &srcu_sync_ops, &srcu_expedited_ops,
+ &srcu_raw_ops, &srcu_raw_sync_ops,
&sched_ops, &sched_sync_ops, &sched_expedited_ops, };
mutex_lock(&fullstop_mutex);
struct task_struct *idle = idle_task(smp_processor_id());
trace_rcu_dyntick("Error on entry: not idle task", oldval, 0);
- ftrace_dump(DUMP_ALL);
+ ftrace_dump(DUMP_ORIG);
WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
current->pid, current->comm,
idle->pid, idle->comm); /* must be idle task! */
trace_rcu_dyntick("Error on exit: not idle task",
oldval, rdtp->dynticks_nesting);
- ftrace_dump(DUMP_ALL);
+ ftrace_dump(DUMP_ORIG);
WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
current->pid, current->comm,
idle->pid, idle->comm); /* must be idle task! */
WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
}
-#ifdef CONFIG_PROVE_RCU
-
/**
* rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
*
}
EXPORT_SYMBOL(rcu_is_cpu_idle);
-#ifdef CONFIG_HOTPLUG_CPU
+#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
/*
* Is the current CPU online? Disable preemption to avoid false positives
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-
-#endif /* #ifdef CONFIG_PROVE_RCU */
+#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
/**
* rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
int cpu;
long delta;
unsigned long flags;
- int ndetected;
+ int ndetected = 0;
struct rcu_node *rnp = rcu_get_root(rsp);
/* Only let one CPU complain about others per time interval. */
*/
rnp = rcu_get_root(rsp);
raw_spin_lock_irqsave(&rnp->lock, flags);
- ndetected = rcu_print_task_stall(rnp);
+ ndetected += rcu_print_task_stall(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
print_cpu_stall_info_end();
return ret;
}
+/*
+ * Initialize the specified rcu_data structure's callback list to empty.
+ */
+static void init_callback_list(struct rcu_data *rdp)
+{
+ int i;
+
+ rdp->nxtlist = NULL;
+ for (i = 0; i < RCU_NEXT_SIZE; i++)
+ rdp->nxttail[i] = &rdp->nxtlist;
+}
+
/*
* Advance this CPU's callbacks, but only if the current grace period
* has ended. This may be called only from the CPU to whom the rdp
rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
struct rcu_node *rnp, struct rcu_data *rdp)
{
- int i;
-
/*
* Orphan the callbacks. First adjust the counts. This is safe
* because ->onofflock excludes _rcu_barrier()'s adoption of
rsp->qlen += rdp->qlen;
rdp->n_cbs_orphaned += rdp->qlen;
rdp->qlen_lazy = 0;
- rdp->qlen = 0;
+ ACCESS_ONCE(rdp->qlen) = 0;
}
/*
}
/* Finally, initialize the rcu_data structure's list to empty. */
- rdp->nxtlist = NULL;
- for (i = 0; i < RCU_NEXT_SIZE; i++)
- rdp->nxttail[i] = &rdp->nxtlist;
+ init_callback_list(rdp);
}
/*
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (need_report & RCU_OFL_TASKS_EXP_GP)
rcu_report_exp_rnp(rsp, rnp, true);
+ WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
+ "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
+ cpu, rdp->qlen, rdp->nxtlist);
}
#else /* #ifdef CONFIG_HOTPLUG_CPU */
}
smp_mb(); /* List handling before counting for rcu_barrier(). */
rdp->qlen_lazy -= count_lazy;
- rdp->qlen -= count;
+ ACCESS_ONCE(rdp->qlen) -= count;
rdp->n_cbs_invoked += count;
/* Reinstate batch limit if we have worked down the excess. */
rdp->n_force_qs_snap = rsp->n_force_qs;
} else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
rdp->qlen_last_fqs_check = rdp->qlen;
+ WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
local_irq_restore(flags);
raise_softirq(RCU_SOFTIRQ);
}
+/*
+ * Handle any core-RCU processing required by a call_rcu() invocation.
+ */
+static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
+ struct rcu_head *head, unsigned long flags)
+{
+ /*
+ * If called from an extended quiescent state, invoke the RCU
+ * core in order to force a re-evaluation of RCU's idleness.
+ */
+ if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
+ invoke_rcu_core();
+
+ /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
+ if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
+ return;
+
+ /*
+ * Force the grace period if too many callbacks or too long waiting.
+ * Enforce hysteresis, and don't invoke force_quiescent_state()
+ * if some other CPU has recently done so. Also, don't bother
+ * invoking force_quiescent_state() if the newly enqueued callback
+ * is the only one waiting for a grace period to complete.
+ */
+ if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
+
+ /* Are we ignoring a completed grace period? */
+ rcu_process_gp_end(rsp, rdp);
+ check_for_new_grace_period(rsp, rdp);
+
+ /* Start a new grace period if one not already started. */
+ if (!rcu_gp_in_progress(rsp)) {
+ unsigned long nestflag;
+ struct rcu_node *rnp_root = rcu_get_root(rsp);
+
+ raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
+ rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */
+ } else {
+ /* Give the grace period a kick. */
+ rdp->blimit = LONG_MAX;
+ if (rsp->n_force_qs == rdp->n_force_qs_snap &&
+ *rdp->nxttail[RCU_DONE_TAIL] != head)
+ force_quiescent_state(rsp, 0);
+ rdp->n_force_qs_snap = rsp->n_force_qs;
+ rdp->qlen_last_fqs_check = rdp->qlen;
+ }
+ } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
+ force_quiescent_state(rsp, 1);
+}
+
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
struct rcu_state *rsp, bool lazy)
rdp = this_cpu_ptr(rsp->rda);
/* Add the callback to our list. */
- rdp->qlen++;
+ ACCESS_ONCE(rdp->qlen)++;
if (lazy)
rdp->qlen_lazy++;
else
else
trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
- /* If interrupts were disabled, don't dive into RCU core. */
- if (irqs_disabled_flags(flags)) {
- local_irq_restore(flags);
- return;
- }
-
- /*
- * Force the grace period if too many callbacks or too long waiting.
- * Enforce hysteresis, and don't invoke force_quiescent_state()
- * if some other CPU has recently done so. Also, don't bother
- * invoking force_quiescent_state() if the newly enqueued callback
- * is the only one waiting for a grace period to complete.
- */
- if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
-
- /* Are we ignoring a completed grace period? */
- rcu_process_gp_end(rsp, rdp);
- check_for_new_grace_period(rsp, rdp);
-
- /* Start a new grace period if one not already started. */
- if (!rcu_gp_in_progress(rsp)) {
- unsigned long nestflag;
- struct rcu_node *rnp_root = rcu_get_root(rsp);
-
- raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
- rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */
- } else {
- /* Give the grace period a kick. */
- rdp->blimit = LONG_MAX;
- if (rsp->n_force_qs == rdp->n_force_qs_snap &&
- *rdp->nxttail[RCU_DONE_TAIL] != head)
- force_quiescent_state(rsp, 0);
- rdp->n_force_qs_snap = rsp->n_force_qs;
- rdp->qlen_last_fqs_check = rdp->qlen;
- }
- } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
- force_quiescent_state(rsp, 1);
+ /* Go handle any RCU core processing required. */
+ __call_rcu_core(rsp, rdp, head, flags);
local_irq_restore(flags);
}
* occasionally incorrectly indicate that there are multiple CPUs online
* when there was in fact only one the whole time, as this just adds
* some overhead: RCU still operates correctly.
- *
- * Of course, sampling num_online_cpus() with preemption enabled can
- * give erroneous results if there are concurrent CPU-hotplug operations.
- * For example, given a demonic sequence of preemptions in num_online_cpus()
- * and CPU-hotplug operations, there could be two or more CPUs online at
- * all times, but num_online_cpus() might well return one (or even zero).
- *
- * However, all such demonic sequences require at least one CPU-offline
- * operation. Furthermore, rcu_blocking_is_gp() giving the wrong answer
- * is only a problem if there is an RCU read-side critical section executing
- * throughout. But RCU-sched and RCU-bh read-side critical sections
- * disable either preemption or bh, which prevents a CPU from going offline.
- * Therefore, the only way that rcu_blocking_is_gp() can incorrectly return
- * that there is only one CPU when in fact there was more than one throughout
- * is when there were no RCU readers in the system. If there are no
- * RCU readers, the grace period by definition can be of zero length,
- * regardless of the number of online CPUs.
*/
static inline int rcu_blocking_is_gp(void)
{
+ int ret;
+
might_sleep(); /* Check for RCU read-side critical section. */
- return num_online_cpus() <= 1;
+ preempt_disable();
+ ret = num_online_cpus() <= 1;
+ preempt_enable();
+ return ret;
}
/**
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
- int i;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rcu_get_root(rsp);
/* Set up local state, ensuring consistent view of global state. */
raw_spin_lock_irqsave(&rnp->lock, flags);
rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
- rdp->nxtlist = NULL;
- for (i = 0; i < RCU_NEXT_SIZE; i++)
- rdp->nxttail[i] = &rdp->nxtlist;
+ init_callback_list(rdp);
rdp->qlen_lazy = 0;
- rdp->qlen = 0;
+ ACCESS_ONCE(rdp->qlen) = 0;
rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
/* # times non-lazy CBs posted to CPU. */
unsigned long nonlazy_posted_snap;
/* idle-period nonlazy_posted snapshot. */
+ int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */
#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
};
DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
static struct rcu_state *rcu_state = &rcu_preempt_state;
-static void rcu_read_unlock_special(struct task_struct *t);
static int rcu_preempted_readers_exp(struct rcu_node *rnp);
/*
local_irq_restore(flags);
}
-/*
- * Tree-preemptible RCU implementation for rcu_read_lock().
- * Just increment ->rcu_read_lock_nesting, shared state will be updated
- * if we block.
- */
-void __rcu_read_lock(void)
-{
- current->rcu_read_lock_nesting++;
- barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
-}
-EXPORT_SYMBOL_GPL(__rcu_read_lock);
-
/*
* Check for preempted RCU readers blocking the current grace period
* for the specified rcu_node structure. If the caller needs a reliable
* notify RCU core processing or task having blocked during the RCU
* read-side critical section.
*/
-static noinline void rcu_read_unlock_special(struct task_struct *t)
+void rcu_read_unlock_special(struct task_struct *t)
{
int empty;
int empty_exp;
}
}
-/*
- * Tree-preemptible RCU implementation for rcu_read_unlock().
- * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
- * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
- * invoke rcu_read_unlock_special() to clean up after a context switch
- * in an RCU read-side critical section and other special cases.
- */
-void __rcu_read_unlock(void)
-{
- struct task_struct *t = current;
-
- if (t->rcu_read_lock_nesting != 1)
- --t->rcu_read_lock_nesting;
- else {
- barrier(); /* critical section before exit code. */
- t->rcu_read_lock_nesting = INT_MIN;
- barrier(); /* assign before ->rcu_read_unlock_special load */
- if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
- rcu_read_unlock_special(t);
- barrier(); /* ->rcu_read_unlock_special load before assign */
- t->rcu_read_lock_nesting = 0;
- }
-#ifdef CONFIG_PROVE_LOCKING
- {
- int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
-
- WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
- }
-#endif /* #ifdef CONFIG_PROVE_LOCKING */
-}
-EXPORT_SYMBOL_GPL(__rcu_read_unlock);
-
#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
/*
*/
#define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */
#define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */
-#define RCU_IDLE_GP_DELAY 6 /* Roughly one grace period. */
+#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
+extern int tick_nohz_enabled;
+
/*
* Does the specified flavor of RCU have non-lazy callbacks pending on
* the specified CPU? Both RCU flavor and CPU are specified by the
return 1;
}
/* Set up for the possibility that RCU will post a timer. */
- if (rcu_cpu_has_nonlazy_callbacks(cpu))
- *delta_jiffies = RCU_IDLE_GP_DELAY;
- else
- *delta_jiffies = RCU_IDLE_LAZY_GP_DELAY;
+ if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
+ *delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies,
+ RCU_IDLE_GP_DELAY) - jiffies;
+ } else {
+ *delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY;
+ *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;
+ }
return 0;
}
del_timer(&rdtp->idle_gp_timer);
trace_rcu_prep_idle("Cleanup after idle");
+ rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled);
}
/*
{
struct timer_list *tp;
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+ int tne;
+
+ /* Handle nohz enablement switches conservatively. */
+ tne = ACCESS_ONCE(tick_nohz_enabled);
+ if (tne != rdtp->tick_nohz_enabled_snap) {
+ if (rcu_cpu_has_callbacks(cpu))
+ invoke_rcu_core(); /* force nohz to see update. */
+ rdtp->tick_nohz_enabled_snap = tne;
+ return;
+ }
+ if (!tne)
+ return;
/*
* If this is an idle re-entry, for example, due to use of
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
trace_rcu_prep_idle("Dyntick with callbacks");
rdtp->idle_gp_timer_expires =
- jiffies + RCU_IDLE_GP_DELAY;
+ round_up(jiffies + RCU_IDLE_GP_DELAY,
+ RCU_IDLE_GP_DELAY);
} else {
rdtp->idle_gp_timer_expires =
- jiffies + RCU_IDLE_LAZY_GP_DELAY;
+ round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
trace_rcu_prep_idle("Dyntick with lazy callbacks");
}
tp = &rdtp->idle_gp_timer;
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
+ *cp = '\0';
}
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
/*
* NO HZ enabled ?
*/
-static int tick_nohz_enabled __read_mostly = 1;
+int tick_nohz_enabled __read_mostly = 1;
/*
* Enable / Disable tickless mode
projects / deliverable / linux.git / commitdiff
