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![Paul E. McKenney](/assets/img/avatar_default.png)
This is a port of commit #82e78d80 from TREE_PREEMPT_RCU to TINY_PREEMPT_RCU. This commit uses the fact that current->rcu_boost_mutex is set any time that the RCU_READ_UNLOCK_BOOSTED flag is set in the current->rcu_read_unlock_special bitmask. This allows tests of the bit to be changed to tests of the pointer, which in turn allows the RCU_READ_UNLOCK_BOOSTED flag to be eliminated. Please note that the check of current->rcu_read_unlock_special need not change because any time that RCU_READ_UNLOCK_BOOSTED was set, so was RCU_READ_UNLOCK_BLOCKED. Therefore, __rcu_read_unlock() can continue testing current->rcu_read_unlock_special for non-zero, as before. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
1116 lines
33 KiB
C
1116 lines
33 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition
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* Internal non-public definitions that provide either classic
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* or preemptible semantics.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright (c) 2010 Linaro
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*
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* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#include <linux/kthread.h>
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#include <linux/module.h>
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#include <linux/debugfs.h>
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#include <linux/seq_file.h>
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/* Global control variables for rcupdate callback mechanism. */
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struct rcu_ctrlblk {
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struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
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struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
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struct rcu_head **curtail; /* ->next pointer of last CB. */
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RCU_TRACE(long qlen); /* Number of pending CBs. */
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RCU_TRACE(char *name); /* Name of RCU type. */
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};
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/* Definition for rcupdate control block. */
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static struct rcu_ctrlblk rcu_sched_ctrlblk = {
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.donetail = &rcu_sched_ctrlblk.rcucblist,
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.curtail = &rcu_sched_ctrlblk.rcucblist,
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RCU_TRACE(.name = "rcu_sched")
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};
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static struct rcu_ctrlblk rcu_bh_ctrlblk = {
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.donetail = &rcu_bh_ctrlblk.rcucblist,
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.curtail = &rcu_bh_ctrlblk.rcucblist,
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RCU_TRACE(.name = "rcu_bh")
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};
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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int rcu_scheduler_active __read_mostly;
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EXPORT_SYMBOL_GPL(rcu_scheduler_active);
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#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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#ifdef CONFIG_TINY_PREEMPT_RCU
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#include <linux/delay.h>
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/* Global control variables for preemptible RCU. */
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struct rcu_preempt_ctrlblk {
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struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */
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struct rcu_head **nexttail;
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/* Tasks blocked in a preemptible RCU */
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/* read-side critical section while an */
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/* preemptible-RCU grace period is in */
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/* progress must wait for a later grace */
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/* period. This pointer points to the */
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/* ->next pointer of the last task that */
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/* must wait for a later grace period, or */
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/* to &->rcb.rcucblist if there is no */
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/* such task. */
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struct list_head blkd_tasks;
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/* Tasks blocked in RCU read-side critical */
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/* section. Tasks are placed at the head */
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/* of this list and age towards the tail. */
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struct list_head *gp_tasks;
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/* Pointer to the first task blocking the */
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/* current grace period, or NULL if there */
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/* is no such task. */
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struct list_head *exp_tasks;
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/* Pointer to first task blocking the */
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/* current expedited grace period, or NULL */
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/* if there is no such task. If there */
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/* is no current expedited grace period, */
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/* then there cannot be any such task. */
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#ifdef CONFIG_RCU_BOOST
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struct list_head *boost_tasks;
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/* Pointer to first task that needs to be */
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/* priority-boosted, or NULL if no priority */
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/* boosting is needed. If there is no */
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/* current or expedited grace period, there */
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/* can be no such task. */
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#endif /* #ifdef CONFIG_RCU_BOOST */
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u8 gpnum; /* Current grace period. */
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u8 gpcpu; /* Last grace period blocked by the CPU. */
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u8 completed; /* Last grace period completed. */
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/* If all three are equal, RCU is idle. */
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#ifdef CONFIG_RCU_BOOST
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unsigned long boost_time; /* When to start boosting (jiffies) */
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#endif /* #ifdef CONFIG_RCU_BOOST */
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#ifdef CONFIG_RCU_TRACE
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unsigned long n_grace_periods;
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#ifdef CONFIG_RCU_BOOST
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unsigned long n_tasks_boosted;
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/* Total number of tasks boosted. */
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unsigned long n_exp_boosts;
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/* Number of tasks boosted for expedited GP. */
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unsigned long n_normal_boosts;
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/* Number of tasks boosted for normal GP. */
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unsigned long n_balk_blkd_tasks;
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/* Refused to boost: no blocked tasks. */
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unsigned long n_balk_exp_gp_tasks;
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/* Refused to boost: nothing blocking GP. */
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unsigned long n_balk_boost_tasks;
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/* Refused to boost: already boosting. */
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unsigned long n_balk_notyet;
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/* Refused to boost: not yet time. */
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unsigned long n_balk_nos;
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/* Refused to boost: not sure why, though. */
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/* This can happen due to race conditions. */
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#endif /* #ifdef CONFIG_RCU_BOOST */
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#endif /* #ifdef CONFIG_RCU_TRACE */
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};
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static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
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.rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
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.rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
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.nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
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.blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
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RCU_TRACE(.rcb.name = "rcu_preempt")
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};
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static void rcu_read_unlock_special(struct task_struct *t);
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static int rcu_preempted_readers_exp(void);
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static void rcu_report_exp_done(void);
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/*
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* Return true if the CPU has not yet responded to the current grace period.
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*/
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static int rcu_cpu_blocking_cur_gp(void)
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{
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return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
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}
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/*
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* Check for a running RCU reader. Because there is only one CPU,
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* there can be but one running RCU reader at a time. ;-)
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*
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* Returns zero if there are no running readers. Returns a positive
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* number if there is at least one reader within its RCU read-side
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* critical section. Returns a negative number if an outermost reader
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* is in the midst of exiting from its RCU read-side critical section
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*
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* Returns zero if there are no running readers. Returns a positive
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* number if there is at least one reader within its RCU read-side
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* critical section. Returns a negative number if an outermost reader
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* is in the midst of exiting from its RCU read-side critical section.
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*/
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static int rcu_preempt_running_reader(void)
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{
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return current->rcu_read_lock_nesting;
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}
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/*
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* Check for preempted RCU readers blocking any grace period.
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* If the caller needs a reliable answer, it must disable hard irqs.
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*/
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static int rcu_preempt_blocked_readers_any(void)
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{
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return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
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}
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/*
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* Check for preempted RCU readers blocking the current grace period.
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* If the caller needs a reliable answer, it must disable hard irqs.
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*/
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static int rcu_preempt_blocked_readers_cgp(void)
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{
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return rcu_preempt_ctrlblk.gp_tasks != NULL;
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}
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/*
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* Return true if another preemptible-RCU grace period is needed.
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*/
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static int rcu_preempt_needs_another_gp(void)
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{
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return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
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}
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/*
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* Return true if a preemptible-RCU grace period is in progress.
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* The caller must disable hardirqs.
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*/
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static int rcu_preempt_gp_in_progress(void)
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{
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return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
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}
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/*
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* Advance a ->blkd_tasks-list pointer to the next entry, instead
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* returning NULL if at the end of the list.
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*/
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static struct list_head *rcu_next_node_entry(struct task_struct *t)
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{
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struct list_head *np;
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np = t->rcu_node_entry.next;
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if (np == &rcu_preempt_ctrlblk.blkd_tasks)
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np = NULL;
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return np;
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}
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#ifdef CONFIG_RCU_TRACE
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#ifdef CONFIG_RCU_BOOST
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static void rcu_initiate_boost_trace(void);
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#endif /* #ifdef CONFIG_RCU_BOOST */
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/*
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* Dump additional statistice for TINY_PREEMPT_RCU.
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*/
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static void show_tiny_preempt_stats(struct seq_file *m)
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{
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seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
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rcu_preempt_ctrlblk.rcb.qlen,
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rcu_preempt_ctrlblk.n_grace_periods,
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rcu_preempt_ctrlblk.gpnum,
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rcu_preempt_ctrlblk.gpcpu,
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rcu_preempt_ctrlblk.completed,
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"T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
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"N."[!rcu_preempt_ctrlblk.gp_tasks],
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"E."[!rcu_preempt_ctrlblk.exp_tasks]);
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#ifdef CONFIG_RCU_BOOST
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seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
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" ",
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"B."[!rcu_preempt_ctrlblk.boost_tasks],
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rcu_preempt_ctrlblk.n_tasks_boosted,
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rcu_preempt_ctrlblk.n_exp_boosts,
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rcu_preempt_ctrlblk.n_normal_boosts,
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(int)(jiffies & 0xffff),
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(int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
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seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n",
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" balk",
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rcu_preempt_ctrlblk.n_balk_blkd_tasks,
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rcu_preempt_ctrlblk.n_balk_exp_gp_tasks,
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rcu_preempt_ctrlblk.n_balk_boost_tasks,
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rcu_preempt_ctrlblk.n_balk_notyet,
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rcu_preempt_ctrlblk.n_balk_nos);
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#endif /* #ifdef CONFIG_RCU_BOOST */
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}
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#endif /* #ifdef CONFIG_RCU_TRACE */
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#ifdef CONFIG_RCU_BOOST
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#include "rtmutex_common.h"
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#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
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/* Controls for rcu_kthread() kthread. */
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static struct task_struct *rcu_kthread_task;
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static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
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static unsigned long have_rcu_kthread_work;
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/*
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* Carry out RCU priority boosting on the task indicated by ->boost_tasks,
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* and advance ->boost_tasks to the next task in the ->blkd_tasks list.
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*/
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static int rcu_boost(void)
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{
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unsigned long flags;
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struct rt_mutex mtx;
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struct task_struct *t;
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struct list_head *tb;
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if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
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rcu_preempt_ctrlblk.exp_tasks == NULL)
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return 0; /* Nothing to boost. */
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raw_local_irq_save(flags);
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/*
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* Recheck with irqs disabled: all tasks in need of boosting
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* might exit their RCU read-side critical sections on their own
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* if we are preempted just before disabling irqs.
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*/
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if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
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rcu_preempt_ctrlblk.exp_tasks == NULL) {
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raw_local_irq_restore(flags);
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return 0;
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}
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/*
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* Preferentially boost tasks blocking expedited grace periods.
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* This cannot starve the normal grace periods because a second
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* expedited grace period must boost all blocked tasks, including
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* those blocking the pre-existing normal grace period.
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*/
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if (rcu_preempt_ctrlblk.exp_tasks != NULL) {
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tb = rcu_preempt_ctrlblk.exp_tasks;
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RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
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} else {
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tb = rcu_preempt_ctrlblk.boost_tasks;
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RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
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}
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RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
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/*
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* We boost task t by manufacturing an rt_mutex that appears to
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* be held by task t. We leave a pointer to that rt_mutex where
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* task t can find it, and task t will release the mutex when it
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* exits its outermost RCU read-side critical section. Then
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* simply acquiring this artificial rt_mutex will boost task
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* t's priority. (Thanks to tglx for suggesting this approach!)
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*/
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t = container_of(tb, struct task_struct, rcu_node_entry);
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rt_mutex_init_proxy_locked(&mtx, t);
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t->rcu_boost_mutex = &mtx;
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raw_local_irq_restore(flags);
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rt_mutex_lock(&mtx);
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rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
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return ACCESS_ONCE(rcu_preempt_ctrlblk.boost_tasks) != NULL ||
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ACCESS_ONCE(rcu_preempt_ctrlblk.exp_tasks) != NULL;
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}
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/*
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* Check to see if it is now time to start boosting RCU readers blocking
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* the current grace period, and, if so, tell the rcu_kthread_task to
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* start boosting them. If there is an expedited boost in progress,
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* we wait for it to complete.
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*
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* If there are no blocked readers blocking the current grace period,
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* return 0 to let the caller know, otherwise return 1. Note that this
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* return value is independent of whether or not boosting was done.
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*/
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static int rcu_initiate_boost(void)
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{
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if (!rcu_preempt_blocked_readers_cgp() &&
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rcu_preempt_ctrlblk.exp_tasks == NULL) {
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RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++);
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return 0;
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}
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if (rcu_preempt_ctrlblk.exp_tasks != NULL ||
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(rcu_preempt_ctrlblk.gp_tasks != NULL &&
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rcu_preempt_ctrlblk.boost_tasks == NULL &&
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ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) {
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if (rcu_preempt_ctrlblk.exp_tasks == NULL)
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rcu_preempt_ctrlblk.boost_tasks =
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rcu_preempt_ctrlblk.gp_tasks;
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invoke_rcu_callbacks();
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} else
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RCU_TRACE(rcu_initiate_boost_trace());
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return 1;
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}
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#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
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/*
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* Do priority-boost accounting for the start of a new grace period.
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*/
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static void rcu_preempt_boost_start_gp(void)
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{
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rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
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}
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#else /* #ifdef CONFIG_RCU_BOOST */
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/*
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* If there is no RCU priority boosting, we don't initiate boosting,
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* but we do indicate whether there are blocked readers blocking the
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* current grace period.
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*/
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static int rcu_initiate_boost(void)
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{
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return rcu_preempt_blocked_readers_cgp();
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}
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/*
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* If there is no RCU priority boosting, nothing to do at grace-period start.
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*/
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static void rcu_preempt_boost_start_gp(void)
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{
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}
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#endif /* else #ifdef CONFIG_RCU_BOOST */
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/*
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* Record a preemptible-RCU quiescent state for the specified CPU. Note
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* that this just means that the task currently running on the CPU is
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* in a quiescent state. There might be any number of tasks blocked
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* while in an RCU read-side critical section.
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*
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* Unlike the other rcu_*_qs() functions, callers to this function
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* must disable irqs in order to protect the assignment to
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* ->rcu_read_unlock_special.
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*
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* Because this is a single-CPU implementation, the only way a grace
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* period can end is if the CPU is in a quiescent state. The reason is
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* that a blocked preemptible-RCU reader can exit its critical section
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* only if the CPU is running it at the time. Therefore, when the
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* last task blocking the current grace period exits its RCU read-side
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* critical section, neither the CPU nor blocked tasks will be stopping
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* the current grace period. (In contrast, SMP implementations
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* might have CPUs running in RCU read-side critical sections that
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* block later grace periods -- but this is not possible given only
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* one CPU.)
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*/
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static void rcu_preempt_cpu_qs(void)
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{
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/* Record both CPU and task as having responded to current GP. */
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rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
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current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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/* If there is no GP then there is nothing more to do. */
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if (!rcu_preempt_gp_in_progress())
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return;
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/*
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* Check up on boosting. If there are readers blocking the
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* current grace period, leave.
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*/
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if (rcu_initiate_boost())
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return;
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/* Advance callbacks. */
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rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
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rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
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rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
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/* If there are no blocked readers, next GP is done instantly. */
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if (!rcu_preempt_blocked_readers_any())
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rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
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/* If there are done callbacks, cause them to be invoked. */
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if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
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invoke_rcu_callbacks();
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}
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|
|
|
/*
|
|
* 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++);
|
|
|
|
/* 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);
|
|
}
|
|
|
|
/*
|
|
* 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)
|
|
{
|
|
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);
|
|
}
|
|
|
|
/*
|
|
* 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
|
|
* 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(). */
|
|
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)
|
|
{
|
|
if (!rcu_preempt_running_reader())
|
|
rcu_preempt_cpu_qs();
|
|
return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
|
|
}
|
|
|
|
/*
|
|
* Check for a task exiting while in a preemptible -RCU read-side
|
|
* critical section, clean up if so. No need to issue warnings,
|
|
* as debug_check_no_locks_held() already does this if lockdep
|
|
* is enabled.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (t->rcu_read_lock_nesting == 0)
|
|
return;
|
|
t->rcu_read_lock_nesting = 1;
|
|
__rcu_read_unlock();
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
|
|
|
|
#ifdef CONFIG_RCU_TRACE
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it is not necessary to
|
|
* dump out its statistics.
|
|
*/
|
|
static void show_tiny_preempt_stats(struct seq_file *m)
|
|
{
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_RCU_TRACE */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to check.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to remove.
|
|
*/
|
|
static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to process.
|
|
*/
|
|
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;
|
|
|
|
/*
|
|
* Start up softirq processing of callbacks.
|
|
*/
|
|
void invoke_rcu_callbacks(void)
|
|
{
|
|
if (rcu_scheduler_fully_active)
|
|
raise_softirq(RCU_SOFTIRQ);
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_TRACE
|
|
|
|
/*
|
|
* There is no callback kthread, so this thread is never it.
|
|
*/
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_RCU_TRACE */
|
|
|
|
static int __init rcu_scheduler_really_started(void)
|
|
{
|
|
rcu_scheduler_fully_active = 1;
|
|
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
|
|
raise_softirq(RCU_SOFTIRQ); /* Invoke any callbacks from early boot. */
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_scheduler_really_started);
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
|
#include <linux/kernel_stat.h>
|
|
|
|
/*
|
|
* During boot, we forgive RCU lockdep issues. After this function is
|
|
* invoked, we start taking RCU lockdep issues seriously.
|
|
*/
|
|
void __init rcu_scheduler_starting(void)
|
|
{
|
|
WARN_ON(nr_context_switches() > 0);
|
|
rcu_scheduler_active = 1;
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
|
|
|
|
#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;
|
|
|
|
raw_local_irq_save(flags);
|
|
rcp->qlen -= n;
|
|
raw_local_irq_restore(flags);
|
|
}
|
|
|
|
/*
|
|
* Dump statistics for TINY_RCU, such as they are.
|
|
*/
|
|
static int show_tiny_stats(struct seq_file *m, void *unused)
|
|
{
|
|
show_tiny_preempt_stats(m);
|
|
seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
|
|
seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
|
|
return 0;
|
|
}
|
|
|
|
static int show_tiny_stats_open(struct inode *inode, struct file *file)
|
|
{
|
|
return single_open(file, show_tiny_stats, NULL);
|
|
}
|
|
|
|
static const struct file_operations show_tiny_stats_fops = {
|
|
.owner = THIS_MODULE,
|
|
.open = show_tiny_stats_open,
|
|
.read = seq_read,
|
|
.llseek = seq_lseek,
|
|
.release = single_release,
|
|
};
|
|
|
|
static struct dentry *rcudir;
|
|
|
|
static int __init rcutiny_trace_init(void)
|
|
{
|
|
struct dentry *retval;
|
|
|
|
rcudir = debugfs_create_dir("rcu", NULL);
|
|
if (!rcudir)
|
|
goto free_out;
|
|
retval = debugfs_create_file("rcudata", 0444, rcudir,
|
|
NULL, &show_tiny_stats_fops);
|
|
if (!retval)
|
|
goto free_out;
|
|
return 0;
|
|
free_out:
|
|
debugfs_remove_recursive(rcudir);
|
|
return 1;
|
|
}
|
|
|
|
static void __exit rcutiny_trace_cleanup(void)
|
|
{
|
|
debugfs_remove_recursive(rcudir);
|
|
}
|
|
|
|
module_init(rcutiny_trace_init);
|
|
module_exit(rcutiny_trace_cleanup);
|
|
|
|
MODULE_AUTHOR("Paul E. McKenney");
|
|
MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
|
|
MODULE_LICENSE("GPL");
|
|
|
|
#endif /* #ifdef CONFIG_RCU_TRACE */
|