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/*
* RCU segmented callback lists
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, you can access it online at
* http://www.gnu.org/licenses/gpl-2.0.html.
*
* Copyright IBM Corporation, 2017
*
* Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/
#ifndef __INCLUDE_LINUX_RCU_SEGCBLIST_H
#define __INCLUDE_LINUX_RCU_SEGCBLIST_H
/* Simple unsegmented callback lists. */
struct rcu_cblist {
struct rcu_head *head;
struct rcu_head **tail;
long len;
long len_lazy;
};
#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
/* Complicated segmented callback lists. ;-) */
/*
* Index values for segments in rcu_segcblist structure.
*
* The segments are as follows:
*
* [head, *tails[RCU_DONE_TAIL]):
* Callbacks whose grace period has elapsed, and thus can be invoked.
* [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
* Callbacks waiting for the current GP from the current CPU's viewpoint.
* [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
* Callbacks that arrived before the next GP started, again from
* the current CPU's viewpoint. These can be handled by the next GP.
* [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
* Callbacks that might have arrived after the next GP started.
* There is some uncertainty as to when a given GP starts and
* ends, but a CPU knows the exact times if it is the one starting
* or ending the GP. Other CPUs know that the previous GP ends
* before the next one starts.
*
* Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
* empty.
*
* The ->gp_seq[] array contains the grace-period number at which the
* corresponding segment of callbacks will be ready to invoke. A given
* element of this array is meaningful only when the corresponding segment
* is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
* are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
* not yet been assigned a grace-period number).
*/
#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
#define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
#define RCU_NEXT_TAIL 3
#define RCU_CBLIST_NSEGS 4
struct rcu_segcblist {
struct rcu_head *head;
struct rcu_head **tails[RCU_CBLIST_NSEGS];
unsigned long gp_seq[RCU_CBLIST_NSEGS];
long len;
long len_lazy;
};
#define RCU_SEGCBLIST_INITIALIZER(n) \
{ \
.head = NULL, \
.tails[RCU_DONE_TAIL] = &n.head, \
.tails[RCU_WAIT_TAIL] = &n.head, \
.tails[RCU_NEXT_READY_TAIL] = &n.head, \
.tails[RCU_NEXT_TAIL] = &n.head, \
}
#endif /* __INCLUDE_LINUX_RCU_SEGCBLIST_H */
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