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Message-Id: <1369061900-546-1-git-send-email-paulmck@linux.vnet.ibm.com>
Date: Mon, 20 May 2013 07:58:08 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
dhowells@...hat.com, edumazet@...gle.com, darren@...art.com,
fweisbec@...il.com, sbw@....edu,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 01/13] rcu: Remove TINY_PREEMPT_RCU
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
TINY_PREEMPT_RCU adds significant code and complexity, but does not
offer commensurate benefits. People currently using TINY_PREEMPT_RCU
can get much better memory footprint with TINY_RCU, or, if they really
need preemptible RCU, they can use TREE_PREEMPT_RCU with a relatively
minor degradation in memory footprint. Please note that this move
has been widely publicized on LKML (https://lkml.org/lkml/2012/11/12/545)
and on LWN (http://lwn.net/Articles/541037/).
This commit therefore removes TINY_PREEMPT_RCU.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
[ paulmck: Updated to eliminate #else in rcutiny.h as suggested by Josh ]
Reviewed-by: Josh Triplett <josh@...htriplett.org>
---
include/linux/hardirq.h | 2 +-
include/linux/rcupdate.h | 2 +-
include/linux/rcutiny.h | 24 +-
init/Kconfig | 10 +-
kernel/rcutiny_plugin.h | 854 -----------------------------------------------
5 files changed, 5 insertions(+), 887 deletions(-)
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index c1d6555..05bcc09 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -128,7 +128,7 @@ extern void synchronize_irq(unsigned int irq);
# define synchronize_irq(irq) barrier()
#endif
-#if defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
+#if defined(CONFIG_TINY_RCU)
static inline void rcu_nmi_enter(void)
{
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 4ccd68e..b6dc04d 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -277,7 +277,7 @@ void wait_rcu_gp(call_rcu_func_t crf);
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
#include <linux/rcutree.h>
-#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
+#elif defined(CONFIG_TINY_RCU)
#include <linux/rcutiny.h>
#else
#error "Unknown RCU implementation specified to kernel configuration"
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 4e56a9c..d3c094f 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -53,16 +53,7 @@ static inline void rcu_barrier(void)
rcu_barrier_sched(); /* Only one CPU, so only one list of callbacks! */
}
-#else /* #ifdef CONFIG_TINY_RCU */
-
-void synchronize_rcu_expedited(void);
-
-static inline void rcu_barrier(void)
-{
- wait_rcu_gp(call_rcu);
-}
-
-#endif /* #else #ifdef CONFIG_TINY_RCU */
+#endif /* #ifdef CONFIG_TINY_RCU */
static inline void synchronize_rcu_bh(void)
{
@@ -97,18 +88,7 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
return 0;
}
-#else /* #ifdef CONFIG_TINY_RCU */
-
-void rcu_preempt_note_context_switch(void);
-int rcu_preempt_needs_cpu(void);
-
-static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
-{
- *delta_jiffies = ULONG_MAX;
- return rcu_preempt_needs_cpu();
-}
-
-#endif /* #else #ifdef CONFIG_TINY_RCU */
+#endif /* #ifdef CONFIG_TINY_RCU */
static inline void rcu_note_context_switch(int cpu)
{
diff --git a/init/Kconfig b/init/Kconfig
index 9d3a788..a21479e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -458,18 +458,10 @@ config TINY_RCU
is not required. This option greatly reduces the
memory footprint of RCU.
-config TINY_PREEMPT_RCU
- bool "Preemptible UP-only small-memory-footprint RCU"
- depends on PREEMPT && !SMP
- help
- This option selects the RCU implementation that is designed
- for real-time UP systems. This option greatly reduces the
- memory footprint of RCU.
-
endchoice
config PREEMPT_RCU
- def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU )
+ def_bool TREE_PREEMPT_RCU
help
This option enables preemptible-RCU code that is common between
the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 8a23300..29a4dd7 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -102,763 +102,6 @@ static void check_cpu_stalls(void)
RCU_TRACE(check_cpu_stall_preempt());
}
-#ifdef CONFIG_TINY_PREEMPT_RCU
-
-#include <linux/delay.h>
-
-/* Global control variables for preemptible RCU. */
-struct rcu_preempt_ctrlblk {
- struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */
- struct rcu_head **nexttail;
- /* Tasks blocked in a preemptible RCU */
- /* read-side critical section while an */
- /* preemptible-RCU grace period is in */
- /* progress must wait for a later grace */
- /* period. This pointer points to the */
- /* ->next pointer of the last task that */
- /* must wait for a later grace period, or */
- /* to &->rcb.rcucblist if there is no */
- /* such task. */
- struct list_head blkd_tasks;
- /* Tasks blocked in RCU read-side critical */
- /* section. Tasks are placed at the head */
- /* of this list and age towards the tail. */
- struct list_head *gp_tasks;
- /* Pointer to the first task blocking the */
- /* current grace period, or NULL if there */
- /* is no such task. */
- struct list_head *exp_tasks;
- /* Pointer to first task blocking the */
- /* current expedited grace period, or NULL */
- /* if there is no such task. If there */
- /* is no current expedited grace period, */
- /* then there cannot be any such task. */
-#ifdef CONFIG_RCU_BOOST
- struct list_head *boost_tasks;
- /* Pointer to first task that needs to be */
- /* priority-boosted, or NULL if no priority */
- /* boosting is needed. If there is no */
- /* current or expedited grace period, there */
- /* can be no such task. */
-#endif /* #ifdef CONFIG_RCU_BOOST */
- u8 gpnum; /* Current grace period. */
- u8 gpcpu; /* Last grace period blocked by the CPU. */
- u8 completed; /* Last grace period completed. */
- /* If all three are equal, RCU is idle. */
-#ifdef CONFIG_RCU_BOOST
- unsigned long boost_time; /* When to start boosting (jiffies) */
-#endif /* #ifdef CONFIG_RCU_BOOST */
-#ifdef CONFIG_RCU_TRACE
- unsigned long n_grace_periods;
-#ifdef CONFIG_RCU_BOOST
- unsigned long n_tasks_boosted;
- /* Total number of tasks boosted. */
- unsigned long n_exp_boosts;
- /* Number of tasks boosted for expedited GP. */
- unsigned long n_normal_boosts;
- /* Number of tasks boosted for normal GP. */
- unsigned long n_balk_blkd_tasks;
- /* Refused to boost: no blocked tasks. */
- unsigned long n_balk_exp_gp_tasks;
- /* Refused to boost: nothing blocking GP. */
- unsigned long n_balk_boost_tasks;
- /* Refused to boost: already boosting. */
- unsigned long n_balk_notyet;
- /* Refused to boost: not yet time. */
- unsigned long n_balk_nos;
- /* Refused to boost: not sure why, though. */
- /* This can happen due to race conditions. */
-#endif /* #ifdef CONFIG_RCU_BOOST */
-#endif /* #ifdef CONFIG_RCU_TRACE */
-};
-
-static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
- .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
- .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
- .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
- .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
- RCU_TRACE(.rcb.name = "rcu_preempt")
-};
-
-static int rcu_preempted_readers_exp(void);
-static void rcu_report_exp_done(void);
-
-/*
- * Return true if the CPU has not yet responded to the current grace period.
- */
-static int rcu_cpu_blocking_cur_gp(void)
-{
- return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
-}
-
-/*
- * Check for a running RCU reader. Because there is only one CPU,
- * there can be but one running RCU reader at a time. ;-)
- *
- * Returns zero if there are no running readers. Returns a positive
- * number if there is at least one reader within its RCU read-side
- * critical section. Returns a negative number if an outermost reader
- * is in the midst of exiting from its RCU read-side critical section
- *
- * Returns zero if there are no running readers. Returns a positive
- * number if there is at least one reader within its RCU read-side
- * critical section. Returns a negative number if an outermost reader
- * is in the midst of exiting from its RCU read-side critical section.
- */
-static int rcu_preempt_running_reader(void)
-{
- return current->rcu_read_lock_nesting;
-}
-
-/*
- * Check for preempted RCU readers blocking any grace period.
- * If the caller needs a reliable answer, it must disable hard irqs.
- */
-static int rcu_preempt_blocked_readers_any(void)
-{
- return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
-}
-
-/*
- * Check for preempted RCU readers blocking the current grace period.
- * If the caller needs a reliable answer, it must disable hard irqs.
- */
-static int rcu_preempt_blocked_readers_cgp(void)
-{
- return rcu_preempt_ctrlblk.gp_tasks != NULL;
-}
-
-/*
- * Return true if another preemptible-RCU grace period is needed.
- */
-static int rcu_preempt_needs_another_gp(void)
-{
- return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
-}
-
-/*
- * Return true if a preemptible-RCU grace period is in progress.
- * The caller must disable hardirqs.
- */
-static int rcu_preempt_gp_in_progress(void)
-{
- return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
-}
-
-/*
- * Advance a ->blkd_tasks-list pointer to the next entry, instead
- * returning NULL if at the end of the list.
- */
-static struct list_head *rcu_next_node_entry(struct task_struct *t)
-{
- struct list_head *np;
-
- np = t->rcu_node_entry.next;
- if (np == &rcu_preempt_ctrlblk.blkd_tasks)
- np = NULL;
- return np;
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-#ifdef CONFIG_RCU_BOOST
-static void rcu_initiate_boost_trace(void);
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
-/*
- * Dump additional statistice for TINY_PREEMPT_RCU.
- */
-static void show_tiny_preempt_stats(struct seq_file *m)
-{
- seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
- rcu_preempt_ctrlblk.rcb.qlen,
- rcu_preempt_ctrlblk.n_grace_periods,
- rcu_preempt_ctrlblk.gpnum,
- rcu_preempt_ctrlblk.gpcpu,
- rcu_preempt_ctrlblk.completed,
- "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
- "N."[!rcu_preempt_ctrlblk.gp_tasks],
- "E."[!rcu_preempt_ctrlblk.exp_tasks]);
-#ifdef CONFIG_RCU_BOOST
- seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
- " ",
- "B."[!rcu_preempt_ctrlblk.boost_tasks],
- rcu_preempt_ctrlblk.n_tasks_boosted,
- rcu_preempt_ctrlblk.n_exp_boosts,
- rcu_preempt_ctrlblk.n_normal_boosts,
- (int)(jiffies & 0xffff),
- (int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
- seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n",
- " balk",
- rcu_preempt_ctrlblk.n_balk_blkd_tasks,
- rcu_preempt_ctrlblk.n_balk_exp_gp_tasks,
- rcu_preempt_ctrlblk.n_balk_boost_tasks,
- rcu_preempt_ctrlblk.n_balk_notyet,
- rcu_preempt_ctrlblk.n_balk_nos);
-#endif /* #ifdef CONFIG_RCU_BOOST */
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-#ifdef CONFIG_RCU_BOOST
-
-#include "rtmutex_common.h"
-
-#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
-
-/* Controls for rcu_kthread() kthread. */
-static struct task_struct *rcu_kthread_task;
-static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
-static unsigned long have_rcu_kthread_work;
-
-/*
- * Carry out RCU priority boosting on the task indicated by ->boost_tasks,
- * and advance ->boost_tasks to the next task in the ->blkd_tasks list.
- */
-static int rcu_boost(void)
-{
- unsigned long flags;
- struct rt_mutex mtx;
- struct task_struct *t;
- struct list_head *tb;
-
- if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
- rcu_preempt_ctrlblk.exp_tasks == NULL)
- return 0; /* Nothing to boost. */
-
- local_irq_save(flags);
-
- /*
- * Recheck with irqs disabled: all tasks in need of boosting
- * might exit their RCU read-side critical sections on their own
- * if we are preempted just before disabling irqs.
- */
- if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
- rcu_preempt_ctrlblk.exp_tasks == NULL) {
- local_irq_restore(flags);
- return 0;
- }
-
- /*
- * Preferentially boost tasks blocking expedited grace periods.
- * This cannot starve the normal grace periods because a second
- * expedited grace period must boost all blocked tasks, including
- * those blocking the pre-existing normal grace period.
- */
- if (rcu_preempt_ctrlblk.exp_tasks != NULL) {
- tb = rcu_preempt_ctrlblk.exp_tasks;
- RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
- } else {
- tb = rcu_preempt_ctrlblk.boost_tasks;
- RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
- }
- RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
-
- /*
- * We boost task t by manufacturing an rt_mutex that appears to
- * be held by task t. We leave a pointer to that rt_mutex where
- * task t can find it, and task t will release the mutex when it
- * exits its outermost RCU read-side critical section. Then
- * simply acquiring this artificial rt_mutex will boost task
- * t's priority. (Thanks to tglx for suggesting this approach!)
- */
- t = container_of(tb, struct task_struct, rcu_node_entry);
- rt_mutex_init_proxy_locked(&mtx, t);
- t->rcu_boost_mutex = &mtx;
- local_irq_restore(flags);
- rt_mutex_lock(&mtx);
- rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
-
- return ACCESS_ONCE(rcu_preempt_ctrlblk.boost_tasks) != NULL ||
- ACCESS_ONCE(rcu_preempt_ctrlblk.exp_tasks) != NULL;
-}
-
-/*
- * Check to see if it is now time to start boosting RCU readers blocking
- * the current grace period, and, if so, tell the rcu_kthread_task to
- * start boosting them. If there is an expedited boost in progress,
- * we wait for it to complete.
- *
- * If there are no blocked readers blocking the current grace period,
- * return 0 to let the caller know, otherwise return 1. Note that this
- * return value is independent of whether or not boosting was done.
- */
-static int rcu_initiate_boost(void)
-{
- if (!rcu_preempt_blocked_readers_cgp() &&
- rcu_preempt_ctrlblk.exp_tasks == NULL) {
- RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++);
- return 0;
- }
- if (rcu_preempt_ctrlblk.exp_tasks != NULL ||
- (rcu_preempt_ctrlblk.gp_tasks != NULL &&
- rcu_preempt_ctrlblk.boost_tasks == NULL &&
- ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) {
- if (rcu_preempt_ctrlblk.exp_tasks == NULL)
- rcu_preempt_ctrlblk.boost_tasks =
- rcu_preempt_ctrlblk.gp_tasks;
- invoke_rcu_callbacks();
- } else {
- RCU_TRACE(rcu_initiate_boost_trace());
- }
- return 1;
-}
-
-#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
-
-/*
- * Do priority-boost accounting for the start of a new grace period.
- */
-static void rcu_preempt_boost_start_gp(void)
-{
- rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
-}
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-/*
- * If there is no RCU priority boosting, we don't initiate boosting,
- * but we do indicate whether there are blocked readers blocking the
- * current grace period.
- */
-static int rcu_initiate_boost(void)
-{
- return rcu_preempt_blocked_readers_cgp();
-}
-
-/*
- * If there is no RCU priority boosting, nothing to do at grace-period start.
- */
-static void rcu_preempt_boost_start_gp(void)
-{
-}
-
-#endif /* else #ifdef CONFIG_RCU_BOOST */
-
-/*
- * Record a preemptible-RCU quiescent state for the specified CPU. Note
- * that this just means that the task currently running on the CPU is
- * in a quiescent state. There might be any number of tasks blocked
- * while in an RCU read-side critical section.
- *
- * Unlike the other rcu_*_qs() functions, callers to this function
- * must disable irqs in order to protect the assignment to
- * ->rcu_read_unlock_special.
- *
- * Because this is a single-CPU implementation, the only way a grace
- * period can end is if the CPU is in a quiescent state. The reason is
- * that a blocked preemptible-RCU reader can exit its critical section
- * only if the CPU is running it at the time. Therefore, when the
- * last task blocking the current grace period exits its RCU read-side
- * critical section, neither the CPU nor blocked tasks will be stopping
- * the current grace period. (In contrast, SMP implementations
- * might have CPUs running in RCU read-side critical sections that
- * block later grace periods -- but this is not possible given only
- * one CPU.)
- */
-static void rcu_preempt_cpu_qs(void)
-{
- /* Record both CPU and task as having responded to current GP. */
- rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
- current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
-
- /* If there is no GP then there is nothing more to do. */
- if (!rcu_preempt_gp_in_progress())
- return;
- /*
- * Check up on boosting. If there are readers blocking the
- * current grace period, leave.
- */
- if (rcu_initiate_boost())
- return;
-
- /* Advance callbacks. */
- rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
- rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
- rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
-
- /* If there are no blocked readers, next GP is done instantly. */
- if (!rcu_preempt_blocked_readers_any())
- rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
-
- /* If there are done callbacks, cause them to be invoked. */
- if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
- invoke_rcu_callbacks();
-}
-
-/*
- * Start a new RCU grace period if warranted. Hard irqs must be disabled.
- */
-static void rcu_preempt_start_gp(void)
-{
- if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) {
-
- /* Official start of GP. */
- rcu_preempt_ctrlblk.gpnum++;
- RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
- reset_cpu_stall_ticks(&rcu_preempt_ctrlblk.rcb);
-
- /* Any blocked RCU readers block new GP. */
- if (rcu_preempt_blocked_readers_any())
- rcu_preempt_ctrlblk.gp_tasks =
- rcu_preempt_ctrlblk.blkd_tasks.next;
-
- /* Set up for RCU priority boosting. */
- rcu_preempt_boost_start_gp();
-
- /* If there is no running reader, CPU is done with GP. */
- if (!rcu_preempt_running_reader())
- rcu_preempt_cpu_qs();
- }
-}
-
-/*
- * We have entered the scheduler, and the current task might soon be
- * context-switched away from. If this task is in an RCU read-side
- * critical section, we will no longer be able to rely on the CPU to
- * record that fact, so we enqueue the task on the blkd_tasks list.
- * If the task started after the current grace period began, as recorded
- * by ->gpcpu, we enqueue at the beginning of the list. Otherwise
- * before the element referenced by ->gp_tasks (or at the tail if
- * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element.
- * The task will dequeue itself when it exits the outermost enclosing
- * RCU read-side critical section. Therefore, the current grace period
- * cannot be permitted to complete until the ->gp_tasks pointer becomes
- * NULL.
- *
- * Caller must disable preemption.
- */
-void rcu_preempt_note_context_switch(void)
-{
- struct task_struct *t = current;
- unsigned long flags;
-
- local_irq_save(flags); /* must exclude scheduler_tick(). */
- if (rcu_preempt_running_reader() > 0 &&
- (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
-
- /* Possibly blocking in an RCU read-side critical section. */
- t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
-
- /*
- * If this CPU has already checked in, then this task
- * will hold up the next grace period rather than the
- * current grace period. Queue the task accordingly.
- * If the task is queued for the current grace period
- * (i.e., this CPU has not yet passed through a quiescent
- * state for the current grace period), then as long
- * as that task remains queued, the current grace period
- * cannot end.
- */
- list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
- if (rcu_cpu_blocking_cur_gp())
- rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
- } else if (rcu_preempt_running_reader() < 0 &&
- t->rcu_read_unlock_special) {
- /*
- * Complete exit from RCU read-side critical section on
- * behalf of preempted instance of __rcu_read_unlock().
- */
- rcu_read_unlock_special(t);
- }
-
- /*
- * Either we were not in an RCU read-side critical section to
- * begin with, or we have now recorded that critical section
- * globally. Either way, we can now note a quiescent state
- * for this CPU. Again, if we were in an RCU read-side critical
- * section, and if that critical section was blocking the current
- * grace period, then the fact that the task has been enqueued
- * means that current grace period continues to be blocked.
- */
- rcu_preempt_cpu_qs();
- local_irq_restore(flags);
-}
-
-/*
- * 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.
- */
-void rcu_read_unlock_special(struct task_struct *t)
-{
- int empty;
- int empty_exp;
- unsigned long flags;
- struct list_head *np;
-#ifdef CONFIG_RCU_BOOST
- struct rt_mutex *rbmp = NULL;
-#endif /* #ifdef CONFIG_RCU_BOOST */
- int special;
-
- /*
- * NMI handlers cannot block and cannot safely manipulate state.
- * They therefore cannot possibly be special, so just leave.
- */
- if (in_nmi())
- return;
-
- local_irq_save(flags);
-
- /*
- * If RCU core is waiting for this CPU to exit critical section,
- * let it know that we have done so.
- */
- special = t->rcu_read_unlock_special;
- if (special & RCU_READ_UNLOCK_NEED_QS)
- rcu_preempt_cpu_qs();
-
- /* Hardware IRQ handlers cannot block. */
- if (in_irq() || in_serving_softirq()) {
- local_irq_restore(flags);
- return;
- }
-
- /* Clean up if blocked during RCU read-side critical section. */
- if (special & RCU_READ_UNLOCK_BLOCKED) {
- t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
-
- /*
- * Remove this task from the ->blkd_tasks list and adjust
- * any pointers that might have been referencing it.
- */
- empty = !rcu_preempt_blocked_readers_cgp();
- empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
- np = rcu_next_node_entry(t);
- list_del_init(&t->rcu_node_entry);
- if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
- rcu_preempt_ctrlblk.gp_tasks = np;
- if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
- rcu_preempt_ctrlblk.exp_tasks = np;
-#ifdef CONFIG_RCU_BOOST
- if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks)
- rcu_preempt_ctrlblk.boost_tasks = np;
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
- /*
- * If this was the last task on the current list, and if
- * we aren't waiting on the CPU, report the quiescent state
- * and start a new grace period if needed.
- */
- if (!empty && !rcu_preempt_blocked_readers_cgp()) {
- rcu_preempt_cpu_qs();
- rcu_preempt_start_gp();
- }
-
- /*
- * If this was the last task on the expedited lists,
- * then we need wake up the waiting task.
- */
- if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
- rcu_report_exp_done();
- }
-#ifdef CONFIG_RCU_BOOST
- /* Unboost self if was boosted. */
- if (t->rcu_boost_mutex != NULL) {
- rbmp = t->rcu_boost_mutex;
- t->rcu_boost_mutex = NULL;
- rt_mutex_unlock(rbmp);
- }
-#endif /* #ifdef CONFIG_RCU_BOOST */
- local_irq_restore(flags);
-}
-
-/*
- * 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
- * checked elsewhere. This is called from the scheduling-clock interrupt.
- *
- * Caller must disable hard irqs.
- */
-static void rcu_preempt_check_callbacks(void)
-{
- struct task_struct *t = current;
-
- if (rcu_preempt_gp_in_progress() &&
- (!rcu_preempt_running_reader() ||
- !rcu_cpu_blocking_cur_gp()))
- rcu_preempt_cpu_qs();
- if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
- rcu_preempt_ctrlblk.rcb.donetail)
- invoke_rcu_callbacks();
- if (rcu_preempt_gp_in_progress() &&
- rcu_cpu_blocking_cur_gp() &&
- rcu_preempt_running_reader() > 0)
- t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
-}
-
-/*
- * TINY_PREEMPT_RCU has an extra callback-list tail pointer to
- * update, so this is invoked from rcu_process_callbacks() to
- * handle that case. Of course, it is invoked for all flavors of
- * RCU, but RCU callbacks can appear only on one of the lists, and
- * neither ->nexttail nor ->donetail can possibly be NULL, so there
- * is no need for an explicit check.
- */
-static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
-{
- if (rcu_preempt_ctrlblk.nexttail == rcp->donetail)
- rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist;
-}
-
-/*
- * Process callbacks for preemptible RCU.
- */
-static void rcu_preempt_process_callbacks(void)
-{
- __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
-}
-
-/*
- * Queue a preemptible -RCU callback for invocation after a grace period.
- */
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
-{
- unsigned long flags;
-
- debug_rcu_head_queue(head);
- head->func = func;
- head->next = NULL;
-
- local_irq_save(flags);
- *rcu_preempt_ctrlblk.nexttail = head;
- rcu_preempt_ctrlblk.nexttail = &head->next;
- RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++);
- rcu_preempt_start_gp(); /* checks to see if GP needed. */
- local_irq_restore(flags);
-}
-EXPORT_SYMBOL_GPL(call_rcu);
-
-/*
- * synchronize_rcu - wait until a grace period has elapsed.
- *
- * Control will return to the caller some time after a full grace
- * period has elapsed, in other words after all currently executing RCU
- * read-side critical sections have completed. RCU read-side critical
- * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
- * and may be nested.
- */
-void synchronize_rcu(void)
-{
- rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
- !lock_is_held(&rcu_lock_map) &&
- !lock_is_held(&rcu_sched_lock_map),
- "Illegal synchronize_rcu() in RCU read-side critical section");
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
- if (!rcu_scheduler_active)
- return;
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
- WARN_ON_ONCE(rcu_preempt_running_reader());
- if (!rcu_preempt_blocked_readers_any())
- return;
-
- /* Once we get past the fastpath checks, same code as rcu_barrier(). */
- if (rcu_expedited)
- synchronize_rcu_expedited();
- else
- rcu_barrier();
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu);
-
-static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
-static unsigned long sync_rcu_preempt_exp_count;
-static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
-
-/*
- * Return non-zero if there are any tasks in RCU read-side critical
- * sections blocking the current preemptible-RCU expedited grace period.
- * If there is no preemptible-RCU expedited grace period currently in
- * progress, returns zero unconditionally.
- */
-static int rcu_preempted_readers_exp(void)
-{
- return rcu_preempt_ctrlblk.exp_tasks != NULL;
-}
-
-/*
- * Report the exit from RCU read-side critical section for the last task
- * that queued itself during or before the current expedited preemptible-RCU
- * grace period.
- */
-static void rcu_report_exp_done(void)
-{
- wake_up(&sync_rcu_preempt_exp_wq);
-}
-
-/*
- * Wait for an rcu-preempt grace period, but expedite it. The basic idea
- * is to rely in the fact that there is but one CPU, and that it is
- * illegal for a task to invoke synchronize_rcu_expedited() while in a
- * preemptible-RCU read-side critical section. Therefore, any such
- * critical sections must correspond to blocked tasks, which must therefore
- * be on the ->blkd_tasks list. So just record the current head of the
- * list in the ->exp_tasks pointer, and wait for all tasks including and
- * after the task pointed to by ->exp_tasks to drain.
- */
-void synchronize_rcu_expedited(void)
-{
- unsigned long flags;
- struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk;
- unsigned long snap;
-
- barrier(); /* ensure prior action seen before grace period. */
-
- WARN_ON_ONCE(rcu_preempt_running_reader());
-
- /*
- * Acquire lock so that there is only one preemptible RCU grace
- * period in flight. Of course, if someone does the expedited
- * grace period for us while we are acquiring the lock, just leave.
- */
- snap = sync_rcu_preempt_exp_count + 1;
- mutex_lock(&sync_rcu_preempt_exp_mutex);
- if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count))
- goto unlock_mb_ret; /* Others did our work for us. */
-
- local_irq_save(flags);
-
- /*
- * All RCU readers have to already be on blkd_tasks because
- * we cannot legally be executing in an RCU read-side critical
- * section.
- */
-
- /* Snapshot current head of ->blkd_tasks list. */
- rpcp->exp_tasks = rpcp->blkd_tasks.next;
- if (rpcp->exp_tasks == &rpcp->blkd_tasks)
- rpcp->exp_tasks = NULL;
-
- /* Wait for tail of ->blkd_tasks list to drain. */
- if (!rcu_preempted_readers_exp()) {
- local_irq_restore(flags);
- } else {
- rcu_initiate_boost();
- local_irq_restore(flags);
- wait_event(sync_rcu_preempt_exp_wq,
- !rcu_preempted_readers_exp());
- }
-
- /* Clean up and exit. */
- barrier(); /* ensure expedited GP seen before counter increment. */
- sync_rcu_preempt_exp_count++;
-unlock_mb_ret:
- mutex_unlock(&sync_rcu_preempt_exp_mutex);
- barrier(); /* ensure subsequent action seen after grace period. */
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
-
-/*
- * Does preemptible RCU need the CPU to stay out of dynticks mode?
- */
-int rcu_preempt_needs_cpu(void)
-{
- return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
-}
-
-#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
-
#ifdef CONFIG_RCU_TRACE
/*
@@ -895,79 +138,6 @@ static void rcu_preempt_process_callbacks(void)
{
}
-#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
-
-#ifdef CONFIG_RCU_BOOST
-
-/*
- * Wake up rcu_kthread() to process callbacks now eligible for invocation
- * or to boost readers.
- */
-static void invoke_rcu_callbacks(void)
-{
- have_rcu_kthread_work = 1;
- if (rcu_kthread_task != NULL)
- wake_up(&rcu_kthread_wq);
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-/*
- * Is the current CPU running the RCU-callbacks kthread?
- * Caller must have preemption disabled.
- */
-static bool rcu_is_callbacks_kthread(void)
-{
- return rcu_kthread_task == current;
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-/*
- * This kthread invokes RCU callbacks whose grace periods have
- * elapsed. It is awakened as needed, and takes the place of the
- * RCU_SOFTIRQ that is used for this purpose when boosting is disabled.
- * This is a kthread, but it is never stopped, at least not until
- * the system goes down.
- */
-static int rcu_kthread(void *arg)
-{
- unsigned long work;
- unsigned long morework;
- unsigned long flags;
-
- for (;;) {
- wait_event_interruptible(rcu_kthread_wq,
- have_rcu_kthread_work != 0);
- morework = rcu_boost();
- local_irq_save(flags);
- work = have_rcu_kthread_work;
- have_rcu_kthread_work = morework;
- local_irq_restore(flags);
- if (work)
- rcu_process_callbacks(NULL);
- schedule_timeout_interruptible(1); /* Leave CPU for others. */
- }
-
- return 0; /* Not reached, but needed to shut gcc up. */
-}
-
-/*
- * Spawn the kthread that invokes RCU callbacks.
- */
-static int __init rcu_spawn_kthreads(void)
-{
- struct sched_param sp;
-
- rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
- sp.sched_priority = RCU_BOOST_PRIO;
- sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
- return 0;
-}
-early_initcall(rcu_spawn_kthreads);
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
/* Hold off callback invocation until early_initcall() time. */
static int rcu_scheduler_fully_active __read_mostly;
@@ -1001,8 +171,6 @@ static int __init rcu_scheduler_really_started(void)
}
early_initcall(rcu_scheduler_really_started);
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
-
#ifdef CONFIG_DEBUG_LOCK_ALLOC
#include <linux/kernel_stat.h>
@@ -1020,25 +188,6 @@ void __init rcu_scheduler_starting(void)
#ifdef CONFIG_RCU_TRACE
-#ifdef CONFIG_RCU_BOOST
-
-static void rcu_initiate_boost_trace(void)
-{
- if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks))
- rcu_preempt_ctrlblk.n_balk_blkd_tasks++;
- else if (rcu_preempt_ctrlblk.gp_tasks == NULL &&
- rcu_preempt_ctrlblk.exp_tasks == NULL)
- rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++;
- else if (rcu_preempt_ctrlblk.boost_tasks != NULL)
- rcu_preempt_ctrlblk.n_balk_boost_tasks++;
- else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))
- rcu_preempt_ctrlblk.n_balk_notyet++;
- else
- rcu_preempt_ctrlblk.n_balk_nos++;
-}
-
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
{
unsigned long flags;
@@ -1105,9 +254,6 @@ MODULE_LICENSE("GPL");
static void check_cpu_stall_preempt(void)
{
-#ifdef CONFIG_TINY_PREEMPT_RCU
- check_cpu_stall(&rcu_preempt_ctrlblk.rcb);
-#endif /* #ifdef CONFIG_TINY_PREEMPT_RCU */
}
#endif /* #ifdef CONFIG_RCU_TRACE */
--
1.8.1.5
--
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