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         short srcu_idx;                 /* Current reader array element. */
  19         u8 srcu_gp_running;             /* GP workqueue running? */
  20         u8 srcu_gp_waiting;             /* GP waiting for readers? */
  21         struct swait_queue_head srcu_wq;
  22                                         /* Last srcu_read_unlock() wakes GP. */
  23         struct rcu_head *srcu_cb_head;  /* Pending callbacks: Head. */
  24         struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
  25         struct work_struct srcu_work;   /* For driving grace periods. */
  26 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  27         struct lockdep_map dep_map;
  28 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  29 };
  30
  31 void srcu_drive_gp(struct work_struct *wp);
  32
  33 #define __SRCU_STRUCT_INIT(name, __ignored)                             \
  34 {                                                                       \
  35         .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),        \
  36         .srcu_cb_tail = &name.srcu_cb_head,                             \
  37         .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
  38         __SRCU_DEP_MAP_INIT(name)                                       \
  39 }
  40
  41 /*
  42  * This odd _STATIC_ arrangement is needed for API compatibility with
  43  * Tree SRCU, which needs some per-CPU data.
  44  */
  45 #define DEFINE_SRCU(name) \
  46         struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
  47 #define DEFINE_STATIC_SRCU(name) \
  48         static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
  49
  50 void synchronize_srcu(struct srcu_struct *ssp);
  51
  52 /*
  53  * Counts the new reader in the appropriate per-CPU element of the
  54  * srcu_struct.  Can be invoked from irq/bh handlers, but the matching
  55  * __srcu_read_unlock() must be in the same handler instance.  Returns an
  56  * index that must be passed to the matching srcu_read_unlock().
  57  */
  58 static inline int __srcu_read_lock(struct srcu_struct *ssp)
  59 {
  60         int idx;
  61
  62         idx = READ_ONCE(ssp->srcu_idx);
  63         WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
  64         return idx;
  65 }
  66
  67 static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
  68 {
  69         synchronize_srcu(ssp);
  70 }
  71
  72 static inline void srcu_barrier(struct srcu_struct *ssp)
  73 {
  74         synchronize_srcu(ssp);
  75 }
  76
  77 /* Defined here to avoid size increase for non-torture kernels. */
  78 static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
  79                                             char *tt, char *tf)
  80 {
  81         int idx;
  82
  83         idx = READ_ONCE(ssp->srcu_idx) & 0x1;
  84         pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
  85                  tt, tf, idx,
  86                  READ_ONCE(ssp->srcu_lock_nesting[!idx]),
  87                  READ_ONCE(ssp->srcu_lock_nesting[idx]));
  88 }
  89
  90 #endif