include/linux/srcutiny.h

   1 /* SPDX-License-Identifier: GPL-2.0+ */
   2 /*
   3  * Sleepable Read-Copy Update mechanism for mutual exclusion,
   4  *      tiny variant.
   5  *
   6  * Copyright (C) IBM Corporation, 2017
   7  *
   8  * Author: Paul McKenney <paulmck@linux.ibm.com>
   9  */
  10
  11 #ifndef _LINUX_SRCU_TINY_H
  12 #define _LINUX_SRCU_TINY_H
  13
  14 #include <linux/swait.h>
  15
  16 struct srcu_struct {
  17         short srcu_lock_nesting[2];     /* srcu_read_lock() nesting depth. */
  18         unsigned short srcu_idx;        /* Current reader array element in bit 0x2. */
  19         unsigned short srcu_idx_max;    /* Furthest future srcu_idx request. */
  20         u8 srcu_gp_running;             /* GP workqueue running? */
  21         u8 srcu_gp_waiting;             /* GP waiting for readers? */
  22         struct swait_queue_head srcu_wq;
  23                                         /* Last srcu_read_unlock() wakes GP. */
  24         struct rcu_head *srcu_cb_head;  /* Pending callbacks: Head. */
  25         struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
  26         struct work_struct srcu_work;   /* For driving grace periods. */
  27 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  28         struct lockdep_map dep_map;
  29 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  30 };
  31
  32 void srcu_drive_gp(struct work_struct *wp);
  33
  34 #define __SRCU_STRUCT_INIT(name, __ignored)                             \
  35 {                                                                       \
  36         .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),        \
  37         .srcu_cb_tail = &name.srcu_cb_head,                             \
  38         .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
  39         __SRCU_DEP_MAP_INIT(name)                                       \
  40 }
  41
  42 /*
  43  * This odd _STATIC_ arrangement is needed for API compatibility with
  44  * Tree SRCU, which needs some per-CPU data.
  45  */
  46 #define DEFINE_SRCU(name) \
  47         struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
  48 #define DEFINE_STATIC_SRCU(name) \
  49         static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
  50
  51 void synchronize_srcu(struct srcu_struct *ssp);
  52
  53 /*
  54  * Counts the new reader in the appropriate per-CPU element of the
  55  * srcu_struct.  Can be invoked from irq/bh handlers, but the matching
  56  * __srcu_read_unlock() must be in the same handler instance.  Returns an
  57  * index that must be passed to the matching srcu_read_unlock().
  58  */
  59 static inline int __srcu_read_lock(struct srcu_struct *ssp)
  60 {
  61         int idx;
  62
  63         idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
  64         WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
  65         return idx;
  66 }
  67
  68 static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
  69 {
  70         synchronize_srcu(ssp);
  71 }
  72
  73 static inline void srcu_barrier(struct srcu_struct *ssp)
  74 {
  75         synchronize_srcu(ssp);
  76 }
  77
  78 /* Defined here to avoid size increase for non-torture kernels. */
  79 static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
  80                                             char *tt, char *tf)
  81 {
  82         int idx;
  83
  84         idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
  85         pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
  86                  tt, tf, idx,
  87                  data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
  88                  data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])));
  89 }
  90
  91 #endif