include/linux/rcu_segcblist.h

   1 /* SPDX-License-Identifier: GPL-2.0+ */
   2 /*
   3  * RCU segmented callback lists
   4  *
   5  * This seemingly RCU-private file must be available to SRCU users
   6  * because the size of the TREE SRCU srcu_struct structure depends
   7  * on these definitions.
   8  *
   9  * Copyright IBM Corporation, 2017
  10  *
  11  * Authors: Paul E. McKenney <paulmck@linux.net.ibm.com>
  12  */
  13
  14 #ifndef __INCLUDE_LINUX_RCU_SEGCBLIST_H
  15 #define __INCLUDE_LINUX_RCU_SEGCBLIST_H
  16
  17 /* Simple unsegmented callback lists. */
  18 struct rcu_cblist {
  19         struct rcu_head *head;
  20         struct rcu_head **tail;
  21         long len;
  22         long len_lazy;
  23 };
  24
  25 #define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
  26
  27 /* Complicated segmented callback lists.  ;-) */
  28
  29 /*
  30  * Index values for segments in rcu_segcblist structure.
  31  *
  32  * The segments are as follows:
  33  *
  34  * [head, *tails[RCU_DONE_TAIL]):
  35  *      Callbacks whose grace period has elapsed, and thus can be invoked.
  36  * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
  37  *      Callbacks waiting for the current GP from the current CPU's viewpoint.
  38  * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
  39  *      Callbacks that arrived before the next GP started, again from
  40  *      the current CPU's viewpoint.  These can be handled by the next GP.
  41  * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
  42  *      Callbacks that might have arrived after the next GP started.
  43  *      There is some uncertainty as to when a given GP starts and
  44  *      ends, but a CPU knows the exact times if it is the one starting
  45  *      or ending the GP.  Other CPUs know that the previous GP ends
  46  *      before the next one starts.
  47  *
  48  * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
  49  * empty.
  50  *
  51  * The ->gp_seq[] array contains the grace-period number at which the
  52  * corresponding segment of callbacks will be ready to invoke.  A given
  53  * element of this array is meaningful only when the corresponding segment
  54  * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
  55  * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
  56  * not yet been assigned a grace-period number).
  57  */
  58 #define RCU_DONE_TAIL           0       /* Also RCU_WAIT head. */
  59 #define RCU_WAIT_TAIL           1       /* Also RCU_NEXT_READY head. */
  60 #define RCU_NEXT_READY_TAIL     2       /* Also RCU_NEXT head. */
  61 #define RCU_NEXT_TAIL           3
  62 #define RCU_CBLIST_NSEGS        4
  63
  64 struct rcu_segcblist {
  65         struct rcu_head *head;
  66         struct rcu_head **tails[RCU_CBLIST_NSEGS];
  67         unsigned long gp_seq[RCU_CBLIST_NSEGS];
  68         long len;
  69         long len_lazy;
  70 };
  71
  72 #define RCU_SEGCBLIST_INITIALIZER(n) \
  73 { \
  74         .head = NULL, \
  75         .tails[RCU_DONE_TAIL] = &n.head, \
  76         .tails[RCU_WAIT_TAIL] = &n.head, \
  77         .tails[RCU_NEXT_READY_TAIL] = &n.head, \
  78         .tails[RCU_NEXT_TAIL] = &n.head, \
  79 }
  80
  81 #endif /* __INCLUDE_LINUX_RCU_SEGCBLIST_H */