include/linux/srcutiny.h

   1 /*
   2  * Sleepable Read-Copy Update mechanism for mutual exclusion,
   3  *      tiny variant.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, you can access it online at
  17  * http://www.gnu.org/licenses/gpl-2.0.html.
  18  *
  19  * Copyright (C) IBM Corporation, 2017
  20  *
  21  * Author: Paul McKenney <paulmck@us.ibm.com>
  22  */
  23
  24 #ifndef _LINUX_SRCU_TINY_H
  25 #define _LINUX_SRCU_TINY_H
  26
  27 #include <linux/swait.h>
  28
  29 struct srcu_struct {
  30         short srcu_lock_nesting[2];     /* srcu_read_lock() nesting depth. */
  31         short srcu_idx;                 /* Current reader array element. */
  32         u8 srcu_gp_running;             /* GP workqueue running? */
  33         u8 srcu_gp_waiting;             /* GP waiting for readers? */
  34         struct swait_queue_head srcu_wq;
  35                                         /* Last srcu_read_unlock() wakes GP. */
  36         struct rcu_head *srcu_cb_head;  /* Pending callbacks: Head. */
  37         struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
  38         struct work_struct srcu_work;   /* For driving grace periods. */
  39 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  40         struct lockdep_map dep_map;
  41 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  42 };
  43
  44 void srcu_drive_gp(struct work_struct *wp);
  45
  46 #define __SRCU_STRUCT_INIT(name)                                        \
  47 {                                                                       \
  48         .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),        \
  49         .srcu_cb_tail = &name.srcu_cb_head,                             \
  50         .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
  51         __SRCU_DEP_MAP_INIT(name)                                       \
  52 }
  53
  54 /*
  55  * This odd _STATIC_ arrangement is needed for API compatibility with
  56  * Tree SRCU, which needs some per-CPU data.
  57  */
  58 #define DEFINE_SRCU(name) \
  59         struct srcu_struct name = __SRCU_STRUCT_INIT(name)
  60 #define DEFINE_STATIC_SRCU(name) \
  61         static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
  62
  63 void synchronize_srcu(struct srcu_struct *sp);
  64
  65 /*
  66  * Counts the new reader in the appropriate per-CPU element of the
  67  * srcu_struct.  Can be invoked from irq/bh handlers, but the matching
  68  * __srcu_read_unlock() must be in the same handler instance.  Returns an
  69  * index that must be passed to the matching srcu_read_unlock().
  70  */
  71 static inline int __srcu_read_lock(struct srcu_struct *sp)
  72 {
  73         int idx;
  74
  75         idx = READ_ONCE(sp->srcu_idx);
  76         WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1);
  77         return idx;
  78 }
  79
  80 static inline void synchronize_srcu_expedited(struct srcu_struct *sp)
  81 {
  82         synchronize_srcu(sp);
  83 }
  84
  85 static inline void srcu_barrier(struct srcu_struct *sp)
  86 {
  87         synchronize_srcu(sp);
  88 }
  89
  90 /* Defined here to avoid size increase for non-torture kernels. */
  91 static inline void srcu_torture_stats_print(struct srcu_struct *sp,
  92                                             char *tt, char *tf)
  93 {
  94         int idx;
  95
  96         idx = READ_ONCE(sp->srcu_idx) & 0x1;
  97         pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
  98                  tt, tf, idx,
  99                  READ_ONCE(sp->srcu_lock_nesting[!idx]),
 100                  READ_ONCE(sp->srcu_lock_nesting[idx]));
 101 }
 102
 103 #endif