include/linux/rcupreempt.h

   1 /*
   2  * Read-Copy Update mechanism for mutual exclusion (RT implementation)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright (C) IBM Corporation, 2006
  19  *
  20  * Author:  Paul McKenney <paulmck@us.ibm.com>
  21  *
  22  * Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>
  23  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  24  * Papers:
  25  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
  26  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
  27  *
  28  * For detailed explanation of Read-Copy Update mechanism see -
  29  *              Documentation/RCU
  30  *
  31  */
  32
  33 #ifndef __LINUX_RCUPREEMPT_H
  34 #define __LINUX_RCUPREEMPT_H
  35
  36 #include <linux/cache.h>
  37 #include <linux/spinlock.h>
  38 #include <linux/threads.h>
  39 #include <linux/percpu.h>
  40 #include <linux/cpumask.h>
  41 #include <linux/seqlock.h>
  42
  43 struct rcu_dyntick_sched {
  44         int dynticks;
  45         int dynticks_snap;
  46         int sched_qs;
  47         int sched_qs_snap;
  48         int sched_dynticks_snap;
  49 };
  50
  51 DECLARE_PER_CPU(struct rcu_dyntick_sched, rcu_dyntick_sched);
  52
  53 static inline void rcu_qsctr_inc(int cpu)
  54 {
  55         struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
  56
  57         rdssp->sched_qs++;
  58 }
  59 #define rcu_bh_qsctr_inc(cpu)
  60
  61 /*
  62  * Someone might want to pass call_rcu_bh as a function pointer.
  63  * So this needs to just be a rename and not a macro function.
  64  *  (no parentheses)
  65  */
  66 #define call_rcu_bh             call_rcu
  67
  68 /**
  69  * call_rcu_sched - Queue RCU callback for invocation after sched grace period.
  70  * @head: structure to be used for queueing the RCU updates.
  71  * @func: actual update function to be invoked after the grace period
  72  *
  73  * The update function will be invoked some time after a full
  74  * synchronize_sched()-style grace period elapses, in other words after
  75  * all currently executing preempt-disabled sections of code (including
  76  * hardirq handlers, NMI handlers, and local_irq_save() blocks) have
  77  * completed.
  78  */
  79 extern void call_rcu_sched(struct rcu_head *head,
  80                            void (*func)(struct rcu_head *head));
  81
  82 extern void __rcu_read_lock(void)       __acquires(RCU);
  83 extern void __rcu_read_unlock(void)     __releases(RCU);
  84 extern int rcu_pending(int cpu);
  85 extern int rcu_needs_cpu(int cpu);
  86
  87 #define __rcu_read_lock_bh()    { rcu_read_lock(); local_bh_disable(); }
  88 #define __rcu_read_unlock_bh()  { local_bh_enable(); rcu_read_unlock(); }
  89
  90 extern void __synchronize_sched(void);
  91
  92 extern void __rcu_init(void);
  93 extern void rcu_init_sched(void);
  94 extern void rcu_check_callbacks(int cpu, int user);
  95 extern void rcu_restart_cpu(int cpu);
  96 extern long rcu_batches_completed(void);
  97
  98 /*
  99  * Return the number of RCU batches processed thus far. Useful for debug
 100  * and statistic. The _bh variant is identifcal to straight RCU
 101  */
 102 static inline long rcu_batches_completed_bh(void)
 103 {
 104         return rcu_batches_completed();
 105 }
 106
 107 #ifdef CONFIG_RCU_TRACE
 108 struct rcupreempt_trace;
 109 extern long *rcupreempt_flipctr(int cpu);
 110 extern long rcupreempt_data_completed(void);
 111 extern int rcupreempt_flip_flag(int cpu);
 112 extern int rcupreempt_mb_flag(int cpu);
 113 extern char *rcupreempt_try_flip_state_name(void);
 114 extern struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu);
 115 #endif
 116
 117 struct softirq_action;
 118
 119 #ifdef CONFIG_NO_HZ
 120
 121 static inline void rcu_enter_nohz(void)
 122 {
 123         static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
 124
 125         smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
 126         __get_cpu_var(rcu_dyntick_sched).dynticks++;
 127         WARN_ON_RATELIMIT(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1, &rs);
 128 }
 129
 130 static inline void rcu_exit_nohz(void)
 131 {
 132         static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
 133
 134         __get_cpu_var(rcu_dyntick_sched).dynticks++;
 135         smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
 136         WARN_ON_RATELIMIT(!(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1),
 137                                 &rs);
 138 }
 139
 140 #else /* CONFIG_NO_HZ */
 141 #define rcu_enter_nohz()        do { } while (0)
 142 #define rcu_exit_nohz()         do { } while (0)
 143 #endif /* CONFIG_NO_HZ */
 144
 145 /*
 146  * A context switch is a grace period for rcupreempt synchronize_rcu()
 147  * only during early boot, before the scheduler has been initialized.
 148  * So, how the heck do we get a context switch?  Well, if the caller
 149  * invokes synchronize_rcu(), they are willing to accept a context
 150  * switch, so we simply pretend that one happened.
 151  *
 152  * After boot, there might be a blocked or preempted task in an RCU
 153  * read-side critical section, so we cannot then take the fastpath.
 154  */
 155 static inline int rcu_blocking_is_gp(void)
 156 {
 157         return num_online_cpus() == 1 && !rcu_scheduler_active;
 158 }
 159
 160 #endif /* __LINUX_RCUPREEMPT_H */