drivers/infiniband/hw/hfi1/mmu_rb.c - linux/kernel/git/bpf/bpf - Git at Google

 /*
  * Copyright(c) 2016 - 2017 Intel Corporation.
  *
  * This file is provided under a dual BSD/GPLv2 license.  When using or
  * redistributing this file, you may do so under either license.
  *
  * GPL LICENSE SUMMARY
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of version 2 of the GNU General Public License as
  * published by the Free Software Foundation.
  *
  * 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.
  *
  * BSD LICENSE
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  *  - Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  *  - Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in
  *    the documentation and/or other materials provided with the
  *    distribution.
  *  - Neither the name of Intel Corporation nor the names of its
  *    contributors may be used to endorse or promote products derived
  *    from this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  */
 #include <linux/list.h>
 #include <linux/rculist.h>
 #include <linux/mmu_notifier.h>
 #include <linux/interval_tree_generic.h>

 #include "mmu_rb.h"
 #include "trace.h"

 struct mmu_rb_handler {
 	struct mmu_notifier mn;
 	struct rb_root_cached root;
 	void *ops_arg;
 	spinlock_t lock;        /* protect the RB tree */
 	struct mmu_rb_ops *ops;
 	struct mm_struct *mm;
 	struct list_head lru_list;
 	struct work_struct del_work;
 	struct list_head del_list;
 	struct workqueue_struct *wq;
 };

 static unsigned long mmu_node_start(struct mmu_rb_node *);
 static unsigned long mmu_node_last(struct mmu_rb_node *);
 static int mmu_notifier_range_start(struct mmu_notifier *,
 		const struct mmu_notifier_range *);
 static struct mmu_rb_node *__mmu_rb_search(struct mmu_rb_handler *,
 					   unsigned long, unsigned long);
 static void do_remove(struct mmu_rb_handler *handler,
 		      struct list_head *del_list);
 static void handle_remove(struct work_struct *work);

 static const struct mmu_notifier_ops mn_opts = {
 	.invalidate_range_start = mmu_notifier_range_start,
 };

 INTERVAL_TREE_DEFINE(struct mmu_rb_node, node, unsigned long, __last,
 		     mmu_node_start, mmu_node_last, static, __mmu_int_rb);

 static unsigned long mmu_node_start(struct mmu_rb_node *node)
 {
 	return node->addr & PAGE_MASK;
 }

 static unsigned long mmu_node_last(struct mmu_rb_node *node)
 {
 	return PAGE_ALIGN(node->addr + node->len) - 1;
 }

 int hfi1_mmu_rb_register(void *ops_arg, struct mm_struct *mm,
 			 struct mmu_rb_ops *ops,
 			 struct workqueue_struct *wq,
 			 struct mmu_rb_handler **handler)
 {
 	struct mmu_rb_handler *handlr;
 	int ret;

 	handlr = kmalloc(sizeof(*handlr), GFP_KERNEL);
 	if (!handlr)
 		return -ENOMEM;

 	handlr->root = RB_ROOT_CACHED;
 	handlr->ops = ops;
 	handlr->ops_arg = ops_arg;
 	INIT_HLIST_NODE(&handlr->mn.hlist);
 	spin_lock_init(&handlr->lock);
 	handlr->mn.ops = &mn_opts;
 	handlr->mm = mm;
 	INIT_WORK(&handlr->del_work, handle_remove);
 	INIT_LIST_HEAD(&handlr->del_list);
 	INIT_LIST_HEAD(&handlr->lru_list);
 	handlr->wq = wq;

 	ret = mmu_notifier_register(&handlr->mn, handlr->mm);
 	if (ret) {
 		kfree(handlr);
 		return ret;
 	}

 	*handler = handlr;
 	return 0;
 }

 void hfi1_mmu_rb_unregister(struct mmu_rb_handler *handler)
 {
 	struct mmu_rb_node *rbnode;
 	struct rb_node *node;
 	unsigned long flags;
 	struct list_head del_list;

 	/* Unregister first so we don't get any more notifications. */
 	mmu_notifier_unregister(&handler->mn, handler->mm);

 	/*
 	 * Make sure the wq delete handler is finished running.  It will not
 	 * be triggered once the mmu notifiers are unregistered above.
 	 */
 	flush_work(&handler->del_work);

 	INIT_LIST_HEAD(&del_list);

 	spin_lock_irqsave(&handler->lock, flags);
 	while ((node = rb_first_cached(&handler->root))) {
 		rbnode = rb_entry(node, struct mmu_rb_node, node);
 		rb_erase_cached(node, &handler->root);
 		/* move from LRU list to delete list */
 		list_move(&rbnode->list, &del_list);
 	}
 	spin_unlock_irqrestore(&handler->lock, flags);

 	do_remove(handler, &del_list);

 	kfree(handler);
 }

 int hfi1_mmu_rb_insert(struct mmu_rb_handler *handler,
 		       struct mmu_rb_node *mnode)
 {
 	struct mmu_rb_node *node;
 	unsigned long flags;
 	int ret = 0;

 	trace_hfi1_mmu_rb_insert(mnode->addr, mnode->len);
 	spin_lock_irqsave(&handler->lock, flags);
 	node = __mmu_rb_search(handler, mnode->addr, mnode->len);
 	if (node) {
 		ret = -EINVAL;
 		goto unlock;
 	}
 	__mmu_int_rb_insert(mnode, &handler->root);
 	list_add(&mnode->list, &handler->lru_list);

 	ret = handler->ops->insert(handler->ops_arg, mnode);
 	if (ret) {
 		__mmu_int_rb_remove(mnode, &handler->root);
 		list_del(&mnode->list); /* remove from LRU list */
 	}
 unlock:
 	spin_unlock_irqrestore(&handler->lock, flags);
 	return ret;
 }

 /* Caller must hold handler lock */
 static struct mmu_rb_node *__mmu_rb_search(struct mmu_rb_handler *handler,
 					   unsigned long addr,
 					   unsigned long len)
 {
 	struct mmu_rb_node *node = NULL;

 	trace_hfi1_mmu_rb_search(addr, len);
 	if (!handler->ops->filter) {
 		node = __mmu_int_rb_iter_first(&handler->root, addr,
 					       (addr + len) - 1);
 	} else {
 		for (node = __mmu_int_rb_iter_first(&handler->root, addr,
 						    (addr + len) - 1);
 		     node;
 		     node = __mmu_int_rb_iter_next(node, addr,
 						   (addr + len) - 1)) {
 			if (handler->ops->filter(node, addr, len))
 				return node;
 		}
 	}
 	return node;
 }

 bool hfi1_mmu_rb_remove_unless_exact(struct mmu_rb_handler *handler,
 				     unsigned long addr, unsigned long len,
 				     struct mmu_rb_node **rb_node)
 {
 	struct mmu_rb_node *node;
 	unsigned long flags;
 	bool ret = false;

 	spin_lock_irqsave(&handler->lock, flags);
 	node = __mmu_rb_search(handler, addr, len);
 	if (node) {
 		if (node->addr == addr && node->len == len)
 			goto unlock;
 		__mmu_int_rb_remove(node, &handler->root);
 		list_del(&node->list); /* remove from LRU list */
 		ret = true;
 	}
 unlock:
 	spin_unlock_irqrestore(&handler->lock, flags);
 	*rb_node = node;
 	return ret;
 }

 void hfi1_mmu_rb_evict(struct mmu_rb_handler *handler, void *evict_arg)
 {
 	struct mmu_rb_node *rbnode, *ptr;
 	struct list_head del_list;
 	unsigned long flags;
 	bool stop = false;

 	INIT_LIST_HEAD(&del_list);

 	spin_lock_irqsave(&handler->lock, flags);
 	list_for_each_entry_safe_reverse(rbnode, ptr, &handler->lru_list,
 					 list) {
 		if (handler->ops->evict(handler->ops_arg, rbnode, evict_arg,
 					&stop)) {
 			__mmu_int_rb_remove(rbnode, &handler->root);
 			/* move from LRU list to delete list */
 			list_move(&rbnode->list, &del_list);
 		}
 		if (stop)
 			break;
 	}
 	spin_unlock_irqrestore(&handler->lock, flags);

 	while (!list_empty(&del_list)) {
 		rbnode = list_first_entry(&del_list, struct mmu_rb_node, list);
 		list_del(&rbnode->list);
 		handler->ops->remove(handler->ops_arg, rbnode);
 	}
 }

 /*
  * It is up to the caller to ensure that this function does not race with the
  * mmu invalidate notifier which may be calling the users remove callback on
  * 'node'.
  */
 void hfi1_mmu_rb_remove(struct mmu_rb_handler *handler,
 			struct mmu_rb_node *node)
 {
 	unsigned long flags;

 	/* Validity of handler and node pointers has been checked by caller. */
 	trace_hfi1_mmu_rb_remove(node->addr, node->len);
 	spin_lock_irqsave(&handler->lock, flags);
 	__mmu_int_rb_remove(node, &handler->root);
 	list_del(&node->list); /* remove from LRU list */
 	spin_unlock_irqrestore(&handler->lock, flags);

 	handler->ops->remove(handler->ops_arg, node);
 }

 static int mmu_notifier_range_start(struct mmu_notifier *mn,
 		const struct mmu_notifier_range *range)
 {
 	struct mmu_rb_handler *handler =
 		container_of(mn, struct mmu_rb_handler, mn);
 	struct rb_root_cached *root = &handler->root;
 	struct mmu_rb_node *node, *ptr = NULL;
 	unsigned long flags;
 	bool added = false;

 	spin_lock_irqsave(&handler->lock, flags);
 	for (node = __mmu_int_rb_iter_first(root, range->start, range->end-1);
 	     node; node = ptr) {
 		/* Guard against node removal. */
 		ptr = __mmu_int_rb_iter_next(node, range->start,
 					     range->end - 1);
 		trace_hfi1_mmu_mem_invalidate(node->addr, node->len);
 		if (handler->ops->invalidate(handler->ops_arg, node)) {
 			__mmu_int_rb_remove(node, root);
 			/* move from LRU list to delete list */
 			list_move(&node->list, &handler->del_list);
 			added = true;
 		}
 	}
 	spin_unlock_irqrestore(&handler->lock, flags);

 	if (added)
 		queue_work(handler->wq, &handler->del_work);

 	return 0;
 }

 /*
  * Call the remove function for the given handler and the list.  This
  * is expected to be called with a delete list extracted from handler.
  * The caller should not be holding the handler lock.
  */
 static void do_remove(struct mmu_rb_handler *handler,
 		      struct list_head *del_list)
 {
 	struct mmu_rb_node *node;

 	while (!list_empty(del_list)) {
 		node = list_first_entry(del_list, struct mmu_rb_node, list);
 		list_del(&node->list);
 		handler->ops->remove(handler->ops_arg, node);
 	}
 }

 /*
  * Work queue function to remove all nodes that have been queued up to
  * be removed.  The key feature is that mm->mmap_sem is not being held
  * and the remove callback can sleep while taking it, if needed.
  */
 static void handle_remove(struct work_struct *work)
 {
 	struct mmu_rb_handler *handler = container_of(work,
 						struct mmu_rb_handler,
 						del_work);
 	struct list_head del_list;
 	unsigned long flags;

 	/* remove anything that is queued to get removed */
 	spin_lock_irqsave(&handler->lock, flags);
 	list_replace_init(&handler->del_list, &del_list);
 	spin_unlock_irqrestore(&handler->lock, flags);

 	do_remove(handler, &del_list);
 }
	/*
	* Copyright(c) 2016 - 2017 Intel Corporation.
	*
	* This file is provided under a dual BSD/GPLv2 license. When using or
	* redistributing this file, you may do so under either license.
	*
	* GPL LICENSE SUMMARY
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of version 2 of the GNU General Public License as
	* published by the Free Software Foundation.
	*
	* 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.
	*
	* BSD LICENSE
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	*
	* - Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* - Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in
	* the documentation and/or other materials provided with the
	* distribution.
	* - Neither the name of Intel Corporation nor the names of its
	* contributors may be used to endorse or promote products derived
	* from this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*
	*/
	#include <linux/list.h>
	#include <linux/rculist.h>
	#include <linux/mmu_notifier.h>
	#include <linux/interval_tree_generic.h>

	#include "mmu_rb.h"
	#include "trace.h"

	struct mmu_rb_handler {
	struct mmu_notifier mn;
	struct rb_root_cached root;
	void *ops_arg;
	spinlock_t lock; /* protect the RB tree */
	struct mmu_rb_ops *ops;
	struct mm_struct *mm;
	struct list_head lru_list;
	struct work_struct del_work;
	struct list_head del_list;
	struct workqueue_struct *wq;
	};

	static unsigned long mmu_node_start(struct mmu_rb_node *);
	static unsigned long mmu_node_last(struct mmu_rb_node *);
	static int mmu_notifier_range_start(struct mmu_notifier *,
	const struct mmu_notifier_range *);
	static struct mmu_rb_node __mmu_rb_search(struct mmu_rb_handler ,
	unsigned long, unsigned long);
	static void do_remove(struct mmu_rb_handler *handler,
	struct list_head *del_list);
	static void handle_remove(struct work_struct *work);

	static const struct mmu_notifier_ops mn_opts = {
	.invalidate_range_start = mmu_notifier_range_start,
	};

	INTERVAL_TREE_DEFINE(struct mmu_rb_node, node, unsigned long, __last,
	mmu_node_start, mmu_node_last, static, __mmu_int_rb);

	static unsigned long mmu_node_start(struct mmu_rb_node *node)
	{
	return node->addr & PAGE_MASK;
	}

	static unsigned long mmu_node_last(struct mmu_rb_node *node)
	{
	return PAGE_ALIGN(node->addr + node->len) - 1;
	}

	int hfi1_mmu_rb_register(void ops_arg, struct mm_struct mm,
	struct mmu_rb_ops *ops,
	struct workqueue_struct *wq,
	struct mmu_rb_handler **handler)
	{
	struct mmu_rb_handler *handlr;
	int ret;

	handlr = kmalloc(sizeof(*handlr), GFP_KERNEL);
	if (!handlr)
	return -ENOMEM;

	handlr->root = RB_ROOT_CACHED;
	handlr->ops = ops;
	handlr->ops_arg = ops_arg;
	INIT_HLIST_NODE(&handlr->mn.hlist);
	spin_lock_init(&handlr->lock);
	handlr->mn.ops = &mn_opts;
	handlr->mm = mm;
	INIT_WORK(&handlr->del_work, handle_remove);
	INIT_LIST_HEAD(&handlr->del_list);
	INIT_LIST_HEAD(&handlr->lru_list);
	handlr->wq = wq;

	ret = mmu_notifier_register(&handlr->mn, handlr->mm);
	if (ret) {
	kfree(handlr);
	return ret;
	}

	*handler = handlr;
	return 0;
	}

	void hfi1_mmu_rb_unregister(struct mmu_rb_handler *handler)
	{
	struct mmu_rb_node *rbnode;
	struct rb_node *node;
	unsigned long flags;
	struct list_head del_list;

	/* Unregister first so we don't get any more notifications. */
	mmu_notifier_unregister(&handler->mn, handler->mm);

	/*
	* Make sure the wq delete handler is finished running. It will not
	* be triggered once the mmu notifiers are unregistered above.
	*/
	flush_work(&handler->del_work);

	INIT_LIST_HEAD(&del_list);

	spin_lock_irqsave(&handler->lock, flags);
	while ((node = rb_first_cached(&handler->root))) {
	rbnode = rb_entry(node, struct mmu_rb_node, node);
	rb_erase_cached(node, &handler->root);
	/* move from LRU list to delete list */
	list_move(&rbnode->list, &del_list);
	}
	spin_unlock_irqrestore(&handler->lock, flags);

	do_remove(handler, &del_list);

	kfree(handler);
	}

	int hfi1_mmu_rb_insert(struct mmu_rb_handler *handler,
	struct mmu_rb_node *mnode)
	{
	struct mmu_rb_node *node;
	unsigned long flags;
	int ret = 0;

	trace_hfi1_mmu_rb_insert(mnode->addr, mnode->len);
	spin_lock_irqsave(&handler->lock, flags);
	node = __mmu_rb_search(handler, mnode->addr, mnode->len);
	if (node) {
	ret = -EINVAL;
	goto unlock;
	}
	__mmu_int_rb_insert(mnode, &handler->root);
	list_add(&mnode->list, &handler->lru_list);

	ret = handler->ops->insert(handler->ops_arg, mnode);
	if (ret) {
	__mmu_int_rb_remove(mnode, &handler->root);
	list_del(&mnode->list); /* remove from LRU list */
	}
	unlock:
	spin_unlock_irqrestore(&handler->lock, flags);
	return ret;
	}

	/* Caller must hold handler lock */
	static struct mmu_rb_node __mmu_rb_search(struct mmu_rb_handler handler,
	unsigned long addr,
	unsigned long len)
	{
	struct mmu_rb_node *node = NULL;

	trace_hfi1_mmu_rb_search(addr, len);
	if (!handler->ops->filter) {
	node = __mmu_int_rb_iter_first(&handler->root, addr,
	(addr + len) - 1);
	} else {
	for (node = __mmu_int_rb_iter_first(&handler->root, addr,
	(addr + len) - 1);
	node;
	node = __mmu_int_rb_iter_next(node, addr,
	(addr + len) - 1)) {
	if (handler->ops->filter(node, addr, len))
	return node;
	}
	}
	return node;
	}

	bool hfi1_mmu_rb_remove_unless_exact(struct mmu_rb_handler *handler,
	unsigned long addr, unsigned long len,
	struct mmu_rb_node **rb_node)
	{
	struct mmu_rb_node *node;
	unsigned long flags;
	bool ret = false;

	spin_lock_irqsave(&handler->lock, flags);
	node = __mmu_rb_search(handler, addr, len);
	if (node) {
	if (node->addr == addr && node->len == len)
	goto unlock;
	__mmu_int_rb_remove(node, &handler->root);
	list_del(&node->list); /* remove from LRU list */
	ret = true;
	}
	unlock:
	spin_unlock_irqrestore(&handler->lock, flags);
	*rb_node = node;
	return ret;
	}

	void hfi1_mmu_rb_evict(struct mmu_rb_handler handler, void evict_arg)
	{
	struct mmu_rb_node rbnode, ptr;
	struct list_head del_list;
	unsigned long flags;
	bool stop = false;

	INIT_LIST_HEAD(&del_list);

	spin_lock_irqsave(&handler->lock, flags);
	list_for_each_entry_safe_reverse(rbnode, ptr, &handler->lru_list,
	list) {
	if (handler->ops->evict(handler->ops_arg, rbnode, evict_arg,
	&stop)) {
	__mmu_int_rb_remove(rbnode, &handler->root);
	/* move from LRU list to delete list */
	list_move(&rbnode->list, &del_list);
	}
	if (stop)
	break;
	}
	spin_unlock_irqrestore(&handler->lock, flags);

	while (!list_empty(&del_list)) {
	rbnode = list_first_entry(&del_list, struct mmu_rb_node, list);
	list_del(&rbnode->list);
	handler->ops->remove(handler->ops_arg, rbnode);
	}
	}

	/*
	* It is up to the caller to ensure that this function does not race with the
	* mmu invalidate notifier which may be calling the users remove callback on
	* 'node'.
	*/
	void hfi1_mmu_rb_remove(struct mmu_rb_handler *handler,
	struct mmu_rb_node *node)
	{
	unsigned long flags;

	/* Validity of handler and node pointers has been checked by caller. */
	trace_hfi1_mmu_rb_remove(node->addr, node->len);
	spin_lock_irqsave(&handler->lock, flags);
	__mmu_int_rb_remove(node, &handler->root);
	list_del(&node->list); /* remove from LRU list */
	spin_unlock_irqrestore(&handler->lock, flags);

	handler->ops->remove(handler->ops_arg, node);
	}

	static int mmu_notifier_range_start(struct mmu_notifier *mn,
	const struct mmu_notifier_range *range)
	{
	struct mmu_rb_handler *handler =
	container_of(mn, struct mmu_rb_handler, mn);
	struct rb_root_cached *root = &handler->root;
	struct mmu_rb_node node, ptr = NULL;
	unsigned long flags;
	bool added = false;

	spin_lock_irqsave(&handler->lock, flags);
	for (node = __mmu_int_rb_iter_first(root, range->start, range->end-1);
	node; node = ptr) {
	/* Guard against node removal. */
	ptr = __mmu_int_rb_iter_next(node, range->start,
	range->end - 1);
	trace_hfi1_mmu_mem_invalidate(node->addr, node->len);
	if (handler->ops->invalidate(handler->ops_arg, node)) {
	__mmu_int_rb_remove(node, root);
	/* move from LRU list to delete list */
	list_move(&node->list, &handler->del_list);
	added = true;
	}
	}
	spin_unlock_irqrestore(&handler->lock, flags);

	if (added)
	queue_work(handler->wq, &handler->del_work);

	return 0;
	}

	/*
	* Call the remove function for the given handler and the list. This
	* is expected to be called with a delete list extracted from handler.
	* The caller should not be holding the handler lock.
	*/
	static void do_remove(struct mmu_rb_handler *handler,
	struct list_head *del_list)
	{
	struct mmu_rb_node *node;

	while (!list_empty(del_list)) {
	node = list_first_entry(del_list, struct mmu_rb_node, list);
	list_del(&node->list);
	handler->ops->remove(handler->ops_arg, node);
	}
	}

	/*
	* Work queue function to remove all nodes that have been queued up to
	* be removed. The key feature is that mm->mmap_sem is not being held
	* and the remove callback can sleep while taking it, if needed.
	*/
	static void handle_remove(struct work_struct *work)
	{
	struct mmu_rb_handler *handler = container_of(work,
	struct mmu_rb_handler,
	del_work);
	struct list_head del_list;
	unsigned long flags;

	/* remove anything that is queued to get removed */
	spin_lock_irqsave(&handler->lock, flags);
	list_replace_init(&handler->del_list, &del_list);
	spin_unlock_irqrestore(&handler->lock, flags);

	do_remove(handler, &del_list);
	}