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