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 // SPDX-License-Identifier: GPL-2.0+
 /*
  * XArray implementation
  * Copyright (c) 2017-2018 Microsoft Corporation
  * Copyright (c) 2018-2020 Oracle
  * Author: Matthew Wilcox <willy@infradead.org>
  */
 
 #include <linux/bitmap.h>
 #include <linux/export.h>
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <linux/xarray.h>
 
 /*
  * Coding conventions in this file:
  *
  * @xa is used to refer to the entire xarray.
  * @xas is the 'xarray operation state'.  It may be either a pointer to
  * an xa_state, or an xa_state stored on the stack.  This is an unfortunate
  * ambiguity.
  * @index is the index of the entry being operated on
  * @mark is an xa_mark_t; a small number indicating one of the mark bits.
  * @node refers to an xa_node; usually the primary one being operated on by
  * this function.
  * @offset is the index into the slots array inside an xa_node.
  * @parent refers to the @xa_node closer to the head than @node.
  * @entry refers to something stored in a slot in the xarray
  */
 
 static inline unsigned int xa_lock_type(const struct xarray *xa)
 {
     return (__force unsigned int)xa->xa_flags & 3;
 }
 
 static inline void xas_lock_type(struct xa_state *xas, unsigned int lock_type)
 {
     if (lock_type == XA_LOCK_IRQ)
         xas_lock_irq(xas);
     else if (lock_type == XA_LOCK_BH)
         xas_lock_bh(xas);
     else
         xas_lock(xas);
 }
 
 static inline void xas_unlock_type(struct xa_state *xas, unsigned int lock_type)
 {
     if (lock_type == XA_LOCK_IRQ)
         xas_unlock_irq(xas);
     else if (lock_type == XA_LOCK_BH)
         xas_unlock_bh(xas);
     else
         xas_unlock(xas);
 }
 
 static inline bool xa_track_free(const struct xarray *xa)
 {
     return xa->xa_flags & XA_FLAGS_TRACK_FREE;
 }
 
 static inline bool xa_zero_busy(const struct xarray *xa)
 {
     return xa->xa_flags & XA_FLAGS_ZERO_BUSY;
 }
 
 static inline void xa_mark_set(struct xarray *xa, xa_mark_t mark)
 {
     if (!(xa->xa_flags & XA_FLAGS_MARK(mark)))
         xa->xa_flags |= XA_FLAGS_MARK(mark);
 }
 
 static inline void xa_mark_clear(struct xarray *xa, xa_mark_t mark)
 {
     if (xa->xa_flags & XA_FLAGS_MARK(mark))
         xa->xa_flags &= ~(XA_FLAGS_MARK(mark));
 }
 
 static inline unsigned long *node_marks(struct xa_node *node, xa_mark_t mark)
 {
     return node->marks[(__force unsigned)mark];
 }
 
 static inline bool node_get_mark(struct xa_node *node,
         unsigned int offset, xa_mark_t mark)
 {
     return test_bit(offset, node_marks(node, mark));
 }
 
 /* returns true if the bit was set */
 static inline bool node_set_mark(struct xa_node *node, unsigned int offset,
                 xa_mark_t mark)
 {
     return __test_and_set_bit(offset, node_marks(node, mark));
 }
 
 /* returns true if the bit was set */
 static inline bool node_clear_mark(struct xa_node *node, unsigned int offset,
                 xa_mark_t mark)
 {
     return __test_and_clear_bit(offset, node_marks(node, mark));
 }
 
 static inline bool node_any_mark(struct xa_node *node, xa_mark_t mark)
 {
     return !bitmap_empty(node_marks(node, mark), XA_CHUNK_SIZE);
 }
 
 static inline void node_mark_all(struct xa_node *node, xa_mark_t mark)
 {
     bitmap_fill(node_marks(node, mark), XA_CHUNK_SIZE);
 }
 
 #define mark_inc(mark) do { \
     mark = (__force xa_mark_t)((__force unsigned)(mark) + 1); \
 } while (0)
 
 /*
  * xas_squash_marks() - Merge all marks to the first entry
  * @xas: Array operation state.
  *
  * Set a mark on the first entry if any entry has it set.  Clear marks on
  * all sibling entries.
  */
 static void xas_squash_marks(const struct xa_state *xas)
 {
     unsigned int mark = 0;
     unsigned int limit = xas->xa_offset + xas->xa_sibs + 1;
 
     if (!xas->xa_sibs)
         return;
 
     do {
         unsigned long *marks = xas->xa_node->marks[mark];
         if (find_next_bit(marks, limit, xas->xa_offset + 1) == limit)
             continue;
         __set_bit(xas->xa_offset, marks);
         bitmap_clear(marks, xas->xa_offset + 1, xas->xa_sibs);
     } while (mark++ != (__force unsigned)XA_MARK_MAX);
 }
 
 /* extracts the offset within this node from the index */
 static unsigned int get_offset(unsigned long index, struct xa_node *node)
 {
     return (index >> node->shift) & XA_CHUNK_MASK;
 }
 
 static void xas_set_offset(struct xa_state *xas)
 {
     xas->xa_offset = get_offset(xas->xa_index, xas->xa_node);
 }
 
 /* move the index either forwards (find) or backwards (sibling slot) */
 static void xas_move_index(struct xa_state *xas, unsigned long offset)
 {
     unsigned int shift = xas->xa_node->shift;
     xas->xa_index &= ~XA_CHUNK_MASK << shift;
     xas->xa_index += offset << shift;
 }
 
 static void xas_next_offset(struct xa_state *xas)
 {
     xas->xa_offset++;
     xas_move_index(xas, xas->xa_offset);
 }
 
 static void *set_bounds(struct xa_state *xas)
 {
     xas->xa_node = XAS_BOUNDS;
     return NULL;
 }
 
 /*
  * Starts a walk.  If the @xas is already valid, we assume that it's on
  * the right path and just return where we've got to.  If we're in an
  * error state, return NULL.  If the index is outside the current scope
  * of the xarray, return NULL without changing @xas->xa_node.  Otherwise
  * set @xas->xa_node to NULL and return the current head of the array.
  */
 static void *xas_start(struct xa_state *xas)
 {
     void *entry;
 
     if (xas_valid(xas))
         return xas_reload(xas);
     if (xas_error(xas))
         return NULL;
 
     entry = xa_head(xas->xa);
     if (!xa_is_node(entry)) {
         if (xas->xa_index)
             return set_bounds(xas);
     } else {
         if ((xas->xa_index >> xa_to_node(entry)->shift) > XA_CHUNK_MASK)
             return set_bounds(xas);
     }
 
     xas->xa_node = NULL;
     return entry;
 }
 
 static void *xas_descend(struct xa_state *xas, struct xa_node *node)
 {
     unsigned int offset = get_offset(xas->xa_index, node);
     void *entry = xa_entry(xas->xa, node, offset);
 
     xas->xa_node = node;
     if (xa_is_sibling(entry)) {
         offset = xa_to_sibling(entry);
         entry = xa_entry(xas->xa, node, offset);
         if (node->shift && xa_is_node(entry))
             entry = XA_RETRY_ENTRY;
     }
 
     xas->xa_offset = offset;
     return entry;
 }
 
 /**
  * xas_load() - Load an entry from the XArray (advanced).
  * @xas: XArray operation state.
  *
  * Usually walks the @xas to the appropriate state to load the entry
  * stored at xa_index.  However, it will do nothing and return %NULL if
  * @xas is in an error state.  xas_load() will never expand the tree.
  *
  * If the xa_state is set up to operate on a multi-index entry, xas_load()
  * may return %NULL or an internal entry, even if there are entries
  * present within the range specified by @xas.
  *
  * Context: Any context.  The caller should hold the xa_lock or the RCU lock.
  * Return: Usually an entry in the XArray, but see description for exceptions.
  */
 void *xas_load(struct xa_state *xas)
 {
     void *entry = xas_start(xas);
 
     while (xa_is_node(entry)) {
         struct xa_node *node = xa_to_node(entry);
 
         if (xas->xa_shift > node->shift)
             break;
         entry = xas_descend(xas, node);
         if (node->shift == 0)
             break;
     }
     return entry;
 }
 EXPORT_SYMBOL_GPL(xas_load);
 
 /* Move the radix tree node cache here */
 extern struct kmem_cache *radix_tree_node_cachep;
 extern void radix_tree_node_rcu_free(struct rcu_head *head);
 
 #define XA_RCU_FREE ((struct xarray *)1)
 
 static void xa_node_free(struct xa_node *node)
 {
     XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
     node->array = XA_RCU_FREE;
     call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
 }
 
 /*
  * xas_destroy() - Free any resources allocated during the XArray operation.
  * @xas: XArray operation state.
  *
  * Most users will not need to call this function; it is called for you
  * by xas_nomem().
  */
 void xas_destroy(struct xa_state *xas)
 {
     struct xa_node *next, *node = xas->xa_alloc;
 
     while (node) {
         XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
         next = rcu_dereference_raw(node->parent);
         radix_tree_node_rcu_free(&node->rcu_head);
         xas->xa_alloc = node = next;
     }
 }
 
 /**
  * xas_nomem() - Allocate memory if needed.
  * @xas: XArray operation state.
  * @gfp: Memory allocation flags.
  *
  * If we need to add new nodes to the XArray, we try to allocate memory
  * with GFP_NOWAIT while holding the lock, which will usually succeed.
  * If it fails, @xas is flagged as needing memory to continue.  The caller
  * should drop the lock and call xas_nomem().  If xas_nomem() succeeds,
  * the caller should retry the operation.
  *
  * Forward progress is guaranteed as one node is allocated here and
  * stored in the xa_state where it will be found by xas_alloc().  More
  * nodes will likely be found in the slab allocator, but we do not tie
  * them up here.
  *
  * Return: true if memory was needed, and was successfully allocated.
  */
 bool xas_nomem(struct xa_state *xas, gfp_t gfp)
 {
     if (xas->xa_node != XA_ERROR(-ENOMEM)) {
         xas_destroy(xas);
         return false;
     }
     if (xas->xa->xa_flags & XA_FLAGS_ACCOUNT)
         gfp |= __GFP_ACCOUNT;
     xas->xa_alloc = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp);
     if (!xas->xa_alloc)
         return false;
     xas->xa_alloc->parent = NULL;
     XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
     xas->xa_node = XAS_RESTART;
     return true;
 }
 EXPORT_SYMBOL_GPL(xas_nomem);
 
 /*
  * __xas_nomem() - Drop locks and allocate memory if needed.
  * @xas: XArray operation state.
  * @gfp: Memory allocation flags.
  *
  * Internal variant of xas_nomem().
  *
  * Return: true if memory was needed, and was successfully allocated.
  */
 static bool __xas_nomem(struct xa_state *xas, gfp_t gfp)
     __must_hold(xas->xa->xa_lock)
 {
     unsigned int lock_type = xa_lock_type(xas->xa);
 
     if (xas->xa_node != XA_ERROR(-ENOMEM)) {
         xas_destroy(xas);
         return false;
     }
     if (xas->xa->xa_flags & XA_FLAGS_ACCOUNT)
         gfp |= __GFP_ACCOUNT;
     if (gfpflags_allow_blocking(gfp)) {
         xas_unlock_type(xas, lock_type);
         xas->xa_alloc = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp);
         xas_lock_type(xas, lock_type);
     } else {
         xas->xa_alloc = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp);
     }
     if (!xas->xa_alloc)
         return false;
     xas->xa_alloc->parent = NULL;
     XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
     xas->xa_node = XAS_RESTART;
     return true;
 }
 
 static void xas_update(struct xa_state *xas, struct xa_node *node)
 {
     if (xas->xa_update)
         xas->xa_update(node);
     else
         XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
 }
 
 static void *xas_alloc(struct xa_state *xas, unsigned int shift)
 {
     struct xa_node *parent = xas->xa_node;
     struct xa_node *node = xas->xa_alloc;
 
     if (xas_invalid(xas))
         return NULL;
 
     if (node) {
         xas->xa_alloc = NULL;
     } else {
         gfp_t gfp = GFP_NOWAIT | __GFP_NOWARN;
 
         if (xas->xa->xa_flags & XA_FLAGS_ACCOUNT)
             gfp |= __GFP_ACCOUNT;
 
         node = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp);
         if (!node) {
             xas_set_err(xas, -ENOMEM);
             return NULL;
         }
     }
 
     if (parent) {
         node->offset = xas->xa_offset;
         parent->count++;
         XA_NODE_BUG_ON(node, parent->count > XA_CHUNK_SIZE);
         xas_update(xas, parent);
     }
     XA_NODE_BUG_ON(node, shift > BITS_PER_LONG);
     XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
     node->shift = shift;
     node->count = 0;
     node->nr_values = 0;
     RCU_INIT_POINTER(node->parent, xas->xa_node);
     node->array = xas->xa;
 
     return node;
 }
 
 #ifdef CONFIG_XARRAY_MULTI
 /* Returns the number of indices covered by a given xa_state */
 static unsigned long xas_size(const struct xa_state *xas)
 {
     return (xas->xa_sibs + 1UL) << xas->xa_shift;
 }
 #endif
 
 /*
  * Use this to calculate the maximum index that will need to be created
  * in order to add the entry described by @xas.  Because we cannot store a
  * multi-index entry at index 0, the calculation is a little more complex
  * than you might expect.
  */
 static unsigned long xas_max(struct xa_state *xas)
 {
     unsigned long max = xas->xa_index;
 
 #ifdef CONFIG_XARRAY_MULTI
     if (xas->xa_shift || xas->xa_sibs) {
         unsigned long mask = xas_size(xas) - 1;
         max |= mask;
         if (mask == max)
             max++;
     }
 #endif
 
     return max;
 }
 
 /* The maximum index that can be contained in the array without expanding it */
 static unsigned long max_index(void *entry)
 {
     if (!xa_is_node(entry))
         return 0;
     return (XA_CHUNK_SIZE << xa_to_node(entry)->shift) - 1;
 }
 
 static void xas_shrink(struct xa_state *xas)
 {
     struct xarray *xa = xas->xa;
     struct xa_node *node = xas->xa_node;
 
     for (;;) {
         void *entry;
 
         XA_NODE_BUG_ON(node, node->count > XA_CHUNK_SIZE);
         if (node->count != 1)
             break;
         entry = xa_entry_locked(xa, node, 0);
         if (!entry)
             break;
         if (!xa_is_node(entry) && node->shift)
             break;
         if (xa_is_zero(entry) && xa_zero_busy(xa))
             entry = NULL;
         xas->xa_node = XAS_BOUNDS;
 
         RCU_INIT_POINTER(xa->xa_head, entry);
         if (xa_track_free(xa) && !node_get_mark(node, 0, XA_FREE_MARK))
             xa_mark_clear(xa, XA_FREE_MARK);
 
         node->count = 0;
         node->nr_values = 0;
         if (!xa_is_node(entry))
             RCU_INIT_POINTER(node->slots[0], XA_RETRY_ENTRY);
         xas_update(xas, node);
         xa_node_free(node);
         if (!xa_is_node(entry))
             break;
         node = xa_to_node(entry);
         node->parent = NULL;
     }
 }
 
 /*
  * xas_delete_node() - Attempt to delete an xa_node
  * @xas: Array operation state.
  *
  * Attempts to delete the @xas->xa_node.  This will fail if xa->node has
  * a non-zero reference count.
  */
 static void xas_delete_node(struct xa_state *xas)
 {
     struct xa_node *node = xas->xa_node;
 
     for (;;) {
         struct xa_node *parent;
 
         XA_NODE_BUG_ON(node, node->count > XA_CHUNK_SIZE);
         if (node->count)
             break;
 
         parent = xa_parent_locked(xas->xa, node);
         xas->xa_node = parent;
         xas->xa_offset = node->offset;
         xa_node_free(node);
 
         if (!parent) {
             xas->xa->xa_head = NULL;
             xas->xa_node = XAS_BOUNDS;
             return;
         }
 
         parent->slots[xas->xa_offset] = NULL;
         parent->count--;
         XA_NODE_BUG_ON(parent, parent->count > XA_CHUNK_SIZE);
         node = parent;
         xas_update(xas, node);
     }
 
     if (!node->parent)
         xas_shrink(xas);
 }
 
 /**
  * xas_free_nodes() - Free this node and all nodes that it references
  * @xas: Array operation state.
  * @top: Node to free
  *
  * This node has been removed from the tree.  We must now free it and all
  * of its subnodes.  There may be RCU walkers with references into the tree,
  * so we must replace all entries with retry markers.
  */
 static void xas_free_nodes(struct xa_state *xas, struct xa_node *top)
 {
     unsigned int offset = 0;
     struct xa_node *node = top;
 
     for (;;) {
         void *entry = xa_entry_locked(xas->xa, node, offset);
 
         if (node->shift && xa_is_node(entry)) {
             node = xa_to_node(entry);
             offset = 0;
             continue;
         }
         if (entry)
             RCU_INIT_POINTER(node->slots[offset], XA_RETRY_ENTRY);
         offset++;
         while (offset == XA_CHUNK_SIZE) {
             struct xa_node *parent;
 
             parent = xa_parent_locked(xas->xa, node);
             offset = node->offset + 1;
             node->count = 0;
             node->nr_values = 0;
             xas_update(xas, node);
             xa_node_free(node);
             if (node == top)
                 return;
             node = parent;
         }
     }
 }
 
 /*
  * xas_expand adds nodes to the head of the tree until it has reached
  * sufficient height to be able to contain @xas->xa_index
  */
 static int xas_expand(struct xa_state *xas, void *head)
 {
     struct xarray *xa = xas->xa;
     struct xa_node *node = NULL;
     unsigned int shift = 0;
     unsigned long max = xas_max(xas);
 
     if (!head) {
         if (max == 0)
             return 0;
         while ((max >> shift) >= XA_CHUNK_SIZE)
             shift += XA_CHUNK_SHIFT;
         return shift + XA_CHUNK_SHIFT;
     } else if (xa_is_node(head)) {
         node = xa_to_node(head);
         shift = node->shift + XA_CHUNK_SHIFT;
     }
     xas->xa_node = NULL;
 
     while (max > max_index(head)) {
         xa_mark_t mark = 0;
 
         XA_NODE_BUG_ON(node, shift > BITS_PER_LONG);
         node = xas_alloc(xas, shift);
         if (!node)
             return -ENOMEM;
 
         node->count = 1;
         if (xa_is_value(head))
             node->nr_values = 1;
         RCU_INIT_POINTER(node->slots[0], head);
 
         /* Propagate the aggregated mark info to the new child */
         for (;;) {
             if (xa_track_free(xa) && mark == XA_FREE_MARK) {
                 node_mark_all(node, XA_FREE_MARK);
                 if (!xa_marked(xa, XA_FREE_MARK)) {
                     node_clear_mark(node, 0, XA_FREE_MARK);
                     xa_mark_set(xa, XA_FREE_MARK);
                 }
             } else if (xa_marked(xa, mark)) {
                 node_set_mark(node, 0, mark);
             }
             if (mark == XA_MARK_MAX)
                 break;
             mark_inc(mark);
         }
 
         /*
          * Now that the new node is fully initialised, we can add
          * it to the tree
          */
         if (xa_is_node(head)) {
             xa_to_node(head)->offset = 0;
             rcu_assign_pointer(xa_to_node(head)->parent, node);
         }
         head = xa_mk_node(node);
         rcu_assign_pointer(xa->xa_head, head);
         xas_update(xas, node);
 
         shift += XA_CHUNK_SHIFT;
     }
 
     xas->xa_node = node;
     return shift;
 }
 
 /*
  * xas_create() - Create a slot to store an entry in.
  * @xas: XArray operation state.
  * @allow_root: %true if we can store the entry in the root directly
  *
  * Most users will not need to call this function directly, as it is called
  * by xas_store().  It is useful for doing conditional store operations
  * (see the xa_cmpxchg() implementation for an example).
  *
  * Return: If the slot already existed, returns the contents of this slot.
  * If the slot was newly created, returns %NULL.  If it failed to create the
  * slot, returns %NULL and indicates the error in @xas.
  */
 static void *xas_create(struct xa_state *xas, bool allow_root)
 {
     struct xarray *xa = xas->xa;
     void *entry;
     void __rcu **slot;
     struct xa_node *node = xas->xa_node;
     int shift;
     unsigned int order = xas->xa_shift;
 
     if (xas_top(node)) {
         entry = xa_head_locked(xa);
         xas->xa_node = NULL;
         if (!entry && xa_zero_busy(xa))
             entry = XA_ZERO_ENTRY;
         shift = xas_expand(xas, entry);
         if (shift < 0)
             return NULL;
         if (!shift && !allow_root)
             shift = XA_CHUNK_SHIFT;
         entry = xa_head_locked(xa);
         slot = &xa->xa_head;
     } else if (xas_error(xas)) {
         return NULL;
     } else if (node) {
         unsigned int offset = xas->xa_offset;
 
         shift = node->shift;
         entry = xa_entry_locked(xa, node, offset);
         slot = &node->slots[offset];
     } else {
         shift = 0;
         entry = xa_head_locked(xa);
         slot = &xa->xa_head;
     }
 
     while (shift > order) {
         shift -= XA_CHUNK_SHIFT;
         if (!entry) {
             node = xas_alloc(xas, shift);
             if (!node)
                 break;
             if (xa_track_free(xa))
                 node_mark_all(node, XA_FREE_MARK);
             rcu_assign_pointer(*slot, xa_mk_node(node));
         } else if (xa_is_node(entry)) {
             node = xa_to_node(entry);
         } else {
             break;
         }
         entry = xas_descend(xas, node);
         slot = &node->slots[xas->xa_offset];
     }
 
     return entry;
 }
 
 /**
  * xas_create_range() - Ensure that stores to this range will succeed
  * @xas: XArray operation state.
  *
  * Creates all of the slots in the range covered by @xas.  Sets @xas to
  * create single-index entries and positions it at the beginning of the
  * range.  This is for the benefit of users which have not yet been
  * converted to use multi-index entries.
  */
 void xas_create_range(struct xa_state *xas)
 {
     unsigned long index = xas->xa_index;
     unsigned char shift = xas->xa_shift;
     unsigned char sibs = xas->xa_sibs;
 
     xas->xa_index |= ((sibs + 1UL) << shift) - 1;
     if (xas_is_node(xas) && xas->xa_node->shift == xas->xa_shift)
         xas->xa_offset |= sibs;
     xas->xa_shift = 0;
     xas->xa_sibs = 0;
 
     for (;;) {
         xas_create(xas, true);
         if (xas_error(xas))
             goto restore;
         if (xas->xa_index <= (index | XA_CHUNK_MASK))
             goto success;
         xas->xa_index -= XA_CHUNK_SIZE;
 
         for (;;) {
             struct xa_node *node = xas->xa_node;
             if (node->shift >= shift)
                 break;
             xas->xa_node = xa_parent_locked(xas->xa, node);
             xas->xa_offset = node->offset - 1;
             if (node->offset != 0)
                 break;
         }
     }
 
 restore:
     xas->xa_shift = shift;
     xas->xa_sibs = sibs;
     xas->xa_index = index;
     return;
 success:
     xas->xa_index = index;
     if (xas->xa_node)
         xas_set_offset(xas);
 }
 EXPORT_SYMBOL_GPL(xas_create_range);
 
 static void update_node(struct xa_state *xas, struct xa_node *node,
         int count, int values)
 {
     if (!node || (!count && !values))
         return;
 
     node->count += count;
     node->nr_values += values;
     XA_NODE_BUG_ON(node, node->count > XA_CHUNK_SIZE);
     XA_NODE_BUG_ON(node, node->nr_values > XA_CHUNK_SIZE);
     xas_update(xas, node);
     if (count < 0)
         xas_delete_node(xas);
 }
 
 /**
  * xas_store() - Store this entry in the XArray.
  * @xas: XArray operation state.
  * @entry: New entry.
  *
  * If @xas is operating on a multi-index entry, the entry returned by this
  * function is essentially meaningless (it may be an internal entry or it
  * may be %NULL, even if there are non-NULL entries at some of the indices
  * covered by the range).  This is not a problem for any current users,
  * and can be changed if needed.
  *
  * Return: The old entry at this index.
  */
 void *xas_store(struct xa_state *xas, void *entry)
 {
     struct xa_node *node;
     void __rcu **slot = &xas->xa->xa_head;
     unsigned int offset, max;
     int count = 0;
     int values = 0;
     void *first, *next;
     bool value = xa_is_value(entry);
 
     if (entry) {
         bool allow_root = !xa_is_node(entry) && !xa_is_zero(entry);
         first = xas_create(xas, allow_root);
     } else {
         first = xas_load(xas);
     }
 
     if (xas_invalid(xas))
         return first;
     node = xas->xa_node;
     if (node && (xas->xa_shift < node->shift))
         xas->xa_sibs = 0;
     if ((first == entry) && !xas->xa_sibs)
         return first;
 
     next = first;
     offset = xas->xa_offset;
     max = xas->xa_offset + xas->xa_sibs;
     if (node) {
         slot = &node->slots[offset];
         if (xas->xa_sibs)
             xas_squash_marks(xas);
     }
     if (!entry)
         xas_init_marks(xas);
 
     for (;;) {
         /*
          * Must clear the marks before setting the entry to NULL,
          * otherwise xas_for_each_marked may find a NULL entry and
          * stop early.  rcu_assign_pointer contains a release barrier
          * so the mark clearing will appear to happen before the
          * entry is set to NULL.
          */
         rcu_assign_pointer(*slot, entry);
         if (xa_is_node(next) && (!node || node->shift))
             xas_free_nodes(xas, xa_to_node(next));
         if (!node)
             break;
         count += !next - !entry;
         values += !xa_is_value(first) - !value;
         if (entry) {
             if (offset == max)
                 break;
             if (!xa_is_sibling(entry))
                 entry = xa_mk_sibling(xas->xa_offset);
         } else {
             if (offset == XA_CHUNK_MASK)
                 break;
         }
         next = xa_entry_locked(xas->xa, node, ++offset);
         if (!xa_is_sibling(next)) {
             if (!entry && (offset > max))
                 break;
             first = next;
         }
         slot++;
     }
 
     update_node(xas, node, count, values);
     return first;
 }
 EXPORT_SYMBOL_GPL(xas_store);
 
 /**
  * xas_get_mark() - Returns the state of this mark.
  * @xas: XArray operation state.
  * @mark: Mark number.
  *
  * Return: true if the mark is set, false if the mark is clear or @xas
  * is in an error state.
  */
 bool xas_get_mark(const struct xa_state *xas, xa_mark_t mark)
 {
     if (xas_invalid(xas))
         return false;
     if (!xas->xa_node)
         return xa_marked(xas->xa, mark);
     return node_get_mark(xas->xa_node, xas->xa_offset, mark);
 }
 EXPORT_SYMBOL_GPL(xas_get_mark);
 
 /**
  * xas_set_mark() - Sets the mark on this entry and its parents.
  * @xas: XArray operation state.
  * @mark: Mark number.
  *
  * Sets the specified mark on this entry, and walks up the tree setting it
  * on all the ancestor entries.  Does nothing if @xas has not been walked to
  * an entry, or is in an error state.
  */
 void xas_set_mark(const struct xa_state *xas, xa_mark_t mark)
 {
     struct xa_node *node = xas->xa_node;
     unsigned int offset = xas->xa_offset;
 
     if (xas_invalid(xas))
         return;
 
     while (node) {
         if (node_set_mark(node, offset, mark))
             return;
         offset = node->offset;
         node = xa_parent_locked(xas->xa, node);
     }
 
     if (!xa_marked(xas->xa, mark))
         xa_mark_set(xas->xa, mark);
 }
 EXPORT_SYMBOL_GPL(xas_set_mark);
 
 /**
  * xas_clear_mark() - Clears the mark on this entry and its parents.
  * @xas: XArray operation state.
  * @mark: Mark number.
  *
  * Clears the specified mark on this entry, and walks back to the head
  * attempting to clear it on all the ancestor entries.  Does nothing if
  * @xas has not been walked to an entry, or is in an error state.
  */
 void xas_clear_mark(const struct xa_state *xas, xa_mark_t mark)
 {
     struct xa_node *node = xas->xa_node;
     unsigned int offset = xas->xa_offset;
 
     if (xas_invalid(xas))
         return;
 
     while (node) {
         if (!node_clear_mark(node, offset, mark))
             return;
         if (node_any_mark(node, mark))
             return;
 
         offset = node->offset;
         node = xa_parent_locked(xas->xa, node);
     }
 
     if (xa_marked(xas->xa, mark))
         xa_mark_clear(xas->xa, mark);
 }
 EXPORT_SYMBOL_GPL(xas_clear_mark);
 
 /**
  * xas_init_marks() - Initialise all marks for the entry
  * @xas: Array operations state.
  *
  * Initialise all marks for the entry specified by @xas.  If we're tracking
  * free entries with a mark, we need to set it on all entries.  All other
  * marks are cleared.
  *
  * This implementation is not as efficient as it could be; we may walk
  * up the tree multiple times.
  */
 void xas_init_marks(const struct xa_state *xas)
 {
     xa_mark_t mark = 0;
 
     for (;;) {
         if (xa_track_free(xas->xa) && mark == XA_FREE_MARK)
             xas_set_mark(xas, mark);
         else
             xas_clear_mark(xas, mark);
         if (mark == XA_MARK_MAX)
             break;
         mark_inc(mark);
     }
 }
 EXPORT_SYMBOL_GPL(xas_init_marks);
 
 #ifdef CONFIG_XARRAY_MULTI
 static unsigned int node_get_marks(struct xa_node *node, unsigned int offset)
 {
     unsigned int marks = 0;
     xa_mark_t mark = XA_MARK_0;
 
     for (;;) {
         if (node_get_mark(node, offset, mark))
             marks |= 1 << (__force unsigned int)mark;
         if (mark == XA_MARK_MAX)
             break;
         mark_inc(mark);
     }
 
     return marks;
 }
 
 static void node_set_marks(struct xa_node *node, unsigned int offset,
             struct xa_node *child, unsigned int marks)
 {
     xa_mark_t mark = XA_MARK_0;
 
     for (;;) {
         if (marks & (1 << (__force unsigned int)mark)) {
             node_set_mark(node, offset, mark);
             if (child)
                 node_mark_all(child, mark);
         }
         if (mark == XA_MARK_MAX)
             break;
         mark_inc(mark);
     }
 }
 
 /**
  * xas_split_alloc() - Allocate memory for splitting an entry.
  * @xas: XArray operation state.
  * @entry: New entry which will be stored in the array.
  * @order: Current entry order.
  * @gfp: Memory allocation flags.
  *
  * This function should be called before calling xas_split().
  * If necessary, it will allocate new nodes (and fill them with @entry)
  * to prepare for the upcoming split of an entry of @order size into
  * entries of the order stored in the @xas.
  *
  * Context: May sleep if @gfp flags permit.
  */
 void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order,
         gfp_t gfp)
 {
     unsigned int sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1;
     unsigned int mask = xas->xa_sibs;
 
     /* XXX: no support for splitting really large entries yet */
     if (WARN_ON(xas->xa_shift + 2 * XA_CHUNK_SHIFT < order))
         goto nomem;
     if (xas->xa_shift + XA_CHUNK_SHIFT > order)
         return;
 
     do {
         unsigned int i;
         void *sibling = NULL;
         struct xa_node *node;
 
         node = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp);
         if (!node)
             goto nomem;
         node->array = xas->xa;
         for (i = 0; i < XA_CHUNK_SIZE; i++) {
             if ((i & mask) == 0) {
                 RCU_INIT_POINTER(node->slots[i], entry);
                 sibling = xa_mk_sibling(i);
             } else {
                 RCU_INIT_POINTER(node->slots[i], sibling);
             }
         }
         RCU_INIT_POINTER(node->parent, xas->xa_alloc);
         xas->xa_alloc = node;
     } while (sibs-- > 0);
 
     return;
 nomem:
     xas_destroy(xas);
     xas_set_err(xas, -ENOMEM);
 }
 EXPORT_SYMBOL_GPL(xas_split_alloc);
 
 /**
  * xas_split() - Split a multi-index entry into smaller entries.
  * @xas: XArray operation state.
  * @entry: New entry to store in the array.
  * @order: Current entry order.
  *
  * The size of the new entries is set in @xas.  The value in @entry is
  * copied to all the replacement entries.
  *
  * Context: Any context.  The caller should hold the xa_lock.
  */
 void xas_split(struct xa_state *xas, void *entry, unsigned int order)
 {
     unsigned int sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1;
     unsigned int offset, marks;
     struct xa_node *node;
     void *curr = xas_load(xas);
     int values = 0;
 
     node = xas->xa_node;
     if (xas_top(node))
         return;
 
     marks = node_get_marks(node, xas->xa_offset);
 
     offset = xas->xa_offset + sibs;
     do {
         if (xas->xa_shift < node->shift) {
             struct xa_node *child = xas->xa_alloc;
 
             xas->xa_alloc = rcu_dereference_raw(child->parent);
             child->shift = node->shift - XA_CHUNK_SHIFT;
             child->offset = offset;
             child->count = XA_CHUNK_SIZE;
             child->nr_values = xa_is_value(entry) ?
                     XA_CHUNK_SIZE : 0;
             RCU_INIT_POINTER(child->parent, node);
             node_set_marks(node, offset, child, marks);
             rcu_assign_pointer(node->slots[offset],
                     xa_mk_node(child));
             if (xa_is_value(curr))
                 values--;
             xas_update(xas, child);
         } else {
             unsigned int canon = offset - xas->xa_sibs;
 
             node_set_marks(node, canon, NULL, marks);
             rcu_assign_pointer(node->slots[canon], entry);
             while (offset > canon)
                 rcu_assign_pointer(node->slots[offset--],
                         xa_mk_sibling(canon));
             values += (xa_is_value(entry) - xa_is_value(curr)) *
                     (xas->xa_sibs + 1);
         }
     } while (offset-- > xas->xa_offset);
 
     node->nr_values += values;
     xas_update(xas, node);
 }
 EXPORT_SYMBOL_GPL(xas_split);
 #endif
 
 /**
  * xas_pause() - Pause a walk to drop a lock.
  * @xas: XArray operation state.
  *
  * Some users need to pause a walk and drop the lock they're holding in
  * order to yield to a higher priority thread or carry out an operation
  * on an entry.  Those users should call this function before they drop
  * the lock.  It resets the @xas to be suitable for the next iteration
  * of the loop after the user has reacquired the lock.  If most entries
  * found during a walk require you to call xas_pause(), the xa_for_each()
  * iterator may be more appropriate.
  *
  * Note that xas_pause() only works for forward iteration.  If a user needs
  * to pause a reverse iteration, we will need a xas_pause_rev().
  */
 void xas_pause(struct xa_state *xas)
 {
     struct xa_node *node = xas->xa_node;
 
     if (xas_invalid(xas))
         return;
 
     xas->xa_node = XAS_RESTART;
     if (node) {
         unsigned long offset = xas->xa_offset;
         while (++offset < XA_CHUNK_SIZE) {
             if (!xa_is_sibling(xa_entry(xas->xa, node, offset)))
                 break;
         }
         xas->xa_index += (offset - xas->xa_offset) << node->shift;
         if (xas->xa_index == 0)
             xas->xa_node = XAS_BOUNDS;
     } else {
         xas->xa_index++;
     }
 }
 EXPORT_SYMBOL_GPL(xas_pause);
 
 /*
  * __xas_prev() - Find the previous entry in the XArray.
  * @xas: XArray operation state.
  *
  * Helper function for xas_prev() which handles all the complex cases
  * out of line.
  */
 void *__xas_prev(struct xa_state *xas)
 {
     void *entry;
 
     if (!xas_frozen(xas->xa_node))
         xas->xa_index--;
     if (!xas->xa_node)
         return set_bounds(xas);
     if (xas_not_node(xas->xa_node))
         return xas_load(xas);
 
     if (xas->xa_offset != get_offset(xas->xa_index, xas->xa_node))
         xas->xa_offset--;
 
     while (xas->xa_offset == 255) {
         xas->xa_offset = xas->xa_node->offset - 1;
         xas->xa_node = xa_parent(xas->xa, xas->xa_node);
         if (!xas->xa_node)
             return set_bounds(xas);
     }
 
     for (;;) {
         entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
         if (!xa_is_node(entry))
             return entry;
 
         xas->xa_node = xa_to_node(entry);
         xas_set_offset(xas);
     }
 }
 EXPORT_SYMBOL_GPL(__xas_prev);
 
 /*
  * __xas_next() - Find the next entry in the XArray.
  * @xas: XArray operation state.
  *
  * Helper function for xas_next() which handles all the complex cases
  * out of line.
  */
 void *__xas_next(struct xa_state *xas)
 {
     void *entry;
 
     if (!xas_frozen(xas->xa_node))
         xas->xa_index++;
     if (!xas->xa_node)
         return set_bounds(xas);
     if (xas_not_node(xas->xa_node))
         return xas_load(xas);
 
     if (xas->xa_offset != get_offset(xas->xa_index, xas->xa_node))
         xas->xa_offset++;
 
     while (xas->xa_offset == XA_CHUNK_SIZE) {
         xas->xa_offset = xas->xa_node->offset + 1;
         xas->xa_node = xa_parent(xas->xa, xas->xa_node);
         if (!xas->xa_node)
             return set_bounds(xas);
     }
 
     for (;;) {
         entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
         if (!xa_is_node(entry))
             return entry;
 
         xas->xa_node = xa_to_node(entry);
         xas_set_offset(xas);
     }
 }
 EXPORT_SYMBOL_GPL(__xas_next);
 
 /**
  * xas_find() - Find the next present entry in the XArray.
  * @xas: XArray operation state.
  * @max: Highest index to return.
  *
  * If the @xas has not yet been walked to an entry, return the entry
  * which has an index >= xas.xa_index.  If it has been walked, the entry
  * currently being pointed at has been processed, and so we move to the
  * next entry.
  *
  * If no entry is found and the array is smaller than @max, the iterator
  * is set to the smallest index not yet in the array.  This allows @xas
  * to be immediately passed to xas_store().
  *
  * Return: The entry, if found, otherwise %NULL.
  */
 void *xas_find(struct xa_state *xas, unsigned long max)
 {
     void *entry;
 
     if (xas_error(xas) || xas->xa_node == XAS_BOUNDS)
         return NULL;
     if (xas->xa_index > max)
         return set_bounds(xas);
 
     if (!xas->xa_node) {
         xas->xa_index = 1;
         return set_bounds(xas);
     } else if (xas->xa_node == XAS_RESTART) {
         entry = xas_load(xas);
         if (entry || xas_not_node(xas->xa_node))
             return entry;
     } else if (!xas->xa_node->shift &&
             xas->xa_offset != (xas->xa_index & XA_CHUNK_MASK)) {
         xas->xa_offset = ((xas->xa_index - 1) & XA_CHUNK_MASK) + 1;
     }
 
     xas_next_offset(xas);
 
     while (xas->xa_node && (xas->xa_index <= max)) {
         if (unlikely(xas->xa_offset == XA_CHUNK_SIZE)) {
             xas->xa_offset = xas->xa_node->offset + 1;
             xas->xa_node = xa_parent(xas->xa, xas->xa_node);
             continue;
         }
 
         entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
         if (xa_is_node(entry)) {
             xas->xa_node = xa_to_node(entry);
             xas->xa_offset = 0;
             continue;
         }
         if (entry && !xa_is_sibling(entry))
             return entry;
 
         xas_next_offset(xas);
     }
 
     if (!xas->xa_node)
         xas->xa_node = XAS_BOUNDS;
     return NULL;
 }
 EXPORT_SYMBOL_GPL(xas_find);
 
 /**
  * xas_find_marked() - Find the next marked entry in the XArray.
  * @xas: XArray operation state.
  * @max: Highest index to return.
  * @mark: Mark number to search for.
  *
  * If the @xas has not yet been walked to an entry, return the marked entry
  * which has an index >= xas.xa_index.  If it has been walked, the entry
  * currently being pointed at has been processed, and so we return the
  * first marked entry with an index > xas.xa_index.
  *
  * If no marked entry is found and the array is smaller than @max, @xas is
  * set to the bounds state and xas->xa_index is set to the smallest index
  * not yet in the array.  This allows @xas to be immediately passed to
  * xas_store().
  *
  * If no entry is found before @max is reached, @xas is set to the restart
  * state.
  *
  * Return: The entry, if found, otherwise %NULL.
  */
 void *xas_find_marked(struct xa_state *xas, unsigned long max, xa_mark_t mark)
 {
     bool advance = true;
     unsigned int offset;
     void *entry;
 
     if (xas_error(xas))
         return NULL;
     if (xas->xa_index > max)
         goto max;
 
     if (!xas->xa_node) {
         xas->xa_index = 1;
         goto out;
     } else if (xas_top(xas->xa_node)) {
         advance = false;
         entry = xa_head(xas->xa);
         xas->xa_node = NULL;
         if (xas->xa_index > max_index(entry))
             goto out;
         if (!xa_is_node(entry)) {
             if (xa_marked(xas->xa, mark))
                 return entry;
             xas->xa_index = 1;
             goto out;
         }
         xas->xa_node = xa_to_node(entry);
         xas->xa_offset = xas->xa_index >> xas->xa_node->shift;
     }
 
     while (xas->xa_index <= max) {
         if (unlikely(xas->xa_offset == XA_CHUNK_SIZE)) {
             xas->xa_offset = xas->xa_node->offset + 1;
             xas->xa_node = xa_parent(xas->xa, xas->xa_node);
             if (!xas->xa_node)
                 break;
             advance = false;
             continue;
         }
 
         if (!advance) {
             entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
             if (xa_is_sibling(entry)) {
                 xas->xa_offset = xa_to_sibling(entry);
                 xas_move_index(xas, xas->xa_offset);
             }
         }
 
         offset = xas_find_chunk(xas, advance, mark);
         if (offset > xas->xa_offset) {
             advance = false;
             xas_move_index(xas, offset);
             /* Mind the wrap */
             if ((xas->xa_index - 1) >= max)
                 goto max;
             xas->xa_offset = offset;
             if (offset == XA_CHUNK_SIZE)
                 continue;
         }
 
         entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
         if (!entry && !(xa_track_free(xas->xa) && mark == XA_FREE_MARK))
             continue;
         if (!xa_is_node(entry))
             return entry;
         xas->xa_node = xa_to_node(entry);
         xas_set_offset(xas);
     }
 
 out:
     if (xas->xa_index > max)
         goto max;
     return set_bounds(xas);
 max:
     xas->xa_node = XAS_RESTART;
     return NULL;
 }
 EXPORT_SYMBOL_GPL(xas_find_marked);
 
 /**
  * xas_find_conflict() - Find the next present entry in a range.
  * @xas: XArray operation state.
  *
  * The @xas describes both a range and a position within that range.
  *
  * Context: Any context.  Expects xa_lock to be held.
  * Return: The next entry in the range covered by @xas or %NULL.
  */
 void *xas_find_conflict(struct xa_state *xas)
 {
     void *curr;
 
     if (xas_error(xas))
         return NULL;
 
     if (!xas->xa_node)
         return NULL;
 
     if (xas_top(xas->xa_node)) {
         curr = xas_start(xas);
         if (!curr)
             return NULL;
         while (xa_is_node(curr)) {
             struct xa_node *node = xa_to_node(curr);
             curr = xas_descend(xas, node);
         }
         if (curr)
             return curr;
     }
 
     if (xas->xa_node->shift > xas->xa_shift)
         return NULL;
 
     for (;;) {
         if (xas->xa_node->shift == xas->xa_shift) {
             if ((xas->xa_offset & xas->xa_sibs) == xas->xa_sibs)
                 break;
         } else if (xas->xa_offset == XA_CHUNK_MASK) {
             xas->xa_offset = xas->xa_node->offset;
             xas->xa_node = xa_parent_locked(xas->xa, xas->xa_node);
             if (!xas->xa_node)
                 break;
             continue;
         }
         curr = xa_entry_locked(xas->xa, xas->xa_node, ++xas->xa_offset);
         if (xa_is_sibling(curr))
             continue;
         while (xa_is_node(curr)) {
             xas->xa_node = xa_to_node(curr);
             xas->xa_offset = 0;
             curr = xa_entry_locked(xas->xa, xas->xa_node, 0);
         }
         if (curr)
             return curr;
     }
     xas->xa_offset -= xas->xa_sibs;
     return NULL;
 }
 EXPORT_SYMBOL_GPL(xas_find_conflict);
 
 /**
  * xa_load() - Load an entry from an XArray.
  * @xa: XArray.
  * @index: index into array.
  *
  * Context: Any context.  Takes and releases the RCU lock.
  * Return: The entry at @index in @xa.
  */
 void *xa_load(struct xarray *xa, unsigned long index)
 {
     XA_STATE(xas, xa, index);
     void *entry;
 
     rcu_read_lock();
     do {
         entry = xas_load(&xas);
         if (xa_is_zero(entry))
             entry = NULL;
     } while (xas_retry(&xas, entry));
     rcu_read_unlock();
 
     return entry;
 }
 EXPORT_SYMBOL(xa_load);
 
 static void *xas_result(struct xa_state *xas, void *curr)
 {
     if (xa_is_zero(curr))
         return NULL;
     if (xas_error(xas))
         curr = xas->xa_node;
     return curr;
 }
 
 /**
  * __xa_erase() - Erase this entry from the XArray while locked.
  * @xa: XArray.
  * @index: Index into array.
  *
  * After this function returns, loading from @index will return %NULL.
  * If the index is part of a multi-index entry, all indices will be erased
  * and none of the entries will be part of a multi-index entry.
  *
  * Context: Any context.  Expects xa_lock to be held on entry.
  * Return: The entry which used to be at this index.
  */
 void *__xa_erase(struct xarray *xa, unsigned long index)
 {
     XA_STATE(xas, xa, index);
     return xas_result(&xas, xas_store(&xas, NULL));
 }
 EXPORT_SYMBOL(__xa_erase);
 
 /**
  * xa_erase() - Erase this entry from the XArray.
  * @xa: XArray.
  * @index: Index of entry.
  *
  * After this function returns, loading from @index will return %NULL.
  * If the index is part of a multi-index entry, all indices will be erased
  * and none of the entries will be part of a multi-index entry.
  *
  * Context: Any context.  Takes and releases the xa_lock.
  * Return: The entry which used to be at this index.
  */
 void *xa_erase(struct xarray *xa, unsigned long index)
 {
     void *entry;
 
     xa_lock(xa);
     entry = __xa_erase(xa, index);
     xa_unlock(xa);
 
     return entry;
 }
 EXPORT_SYMBOL(xa_erase);
 
 /**
  * __xa_store() - Store this entry in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * You must already be holding the xa_lock when calling this function.
  * It will drop the lock if needed to allocate memory, and then reacquire
  * it afterwards.
  *
  * Context: Any context.  Expects xa_lock to be held on entry.  May
  * release and reacquire xa_lock if @gfp flags permit.
  * Return: The old entry at this index or xa_err() if an error happened.
  */
 void *__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
 {
     XA_STATE(xas, xa, index);
     void *curr;
 
     if (WARN_ON_ONCE(xa_is_advanced(entry)))
         return XA_ERROR(-EINVAL);
     if (xa_track_free(xa) && !entry)
         entry = XA_ZERO_ENTRY;
 
     do {
         curr = xas_store(&xas, entry);
         if (xa_track_free(xa))
             xas_clear_mark(&xas, XA_FREE_MARK);
     } while (__xas_nomem(&xas, gfp));
 
     return xas_result(&xas, curr);
 }
 EXPORT_SYMBOL(__xa_store);
 
 /**
  * xa_store() - Store this entry in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * After this function returns, loads from this index will return @entry.
  * Storing into an existing multi-index entry updates the entry of every index.
  * The marks associated with @index are unaffected unless @entry is %NULL.
  *
  * Context: Any context.  Takes and releases the xa_lock.
  * May sleep if the @gfp flags permit.
  * Return: The old entry at this index on success, xa_err(-EINVAL) if @entry
  * cannot be stored in an XArray, or xa_err(-ENOMEM) if memory allocation
  * failed.
  */
 void *xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
 {
     void *curr;
 
     xa_lock(xa);
     curr = __xa_store(xa, index, entry, gfp);
     xa_unlock(xa);
 
     return curr;
 }
 EXPORT_SYMBOL(xa_store);
 
 /**
  * __xa_cmpxchg() - Store this entry in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @old: Old value to test against.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * You must already be holding the xa_lock when calling this function.
  * It will drop the lock if needed to allocate memory, and then reacquire
  * it afterwards.
  *
  * Context: Any context.  Expects xa_lock to be held on entry.  May
  * release and reacquire xa_lock if @gfp flags permit.
  * Return: The old entry at this index or xa_err() if an error happened.
  */
 void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
             void *old, void *entry, gfp_t gfp)
 {
     XA_STATE(xas, xa, index);
     void *curr;
 
     if (WARN_ON_ONCE(xa_is_advanced(entry)))
         return XA_ERROR(-EINVAL);
 
     do {
         curr = xas_load(&xas);
         if (curr == old) {
             xas_store(&xas, entry);
             if (xa_track_free(xa) && entry && !curr)
                 xas_clear_mark(&xas, XA_FREE_MARK);
         }
     } while (__xas_nomem(&xas, gfp));
 
     return xas_result(&xas, curr);
 }
 EXPORT_SYMBOL(__xa_cmpxchg);
 
 /**
  * __xa_insert() - Store this entry in the XArray if no entry is present.
  * @xa: XArray.
  * @index: Index into array.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * Inserting a NULL entry will store a reserved entry (like xa_reserve())
  * if no entry is present.  Inserting will fail if a reserved entry is
  * present, even though loading from this index will return NULL.
  *
  * Context: Any context.  Expects xa_lock to be held on entry.  May
  * release and reacquire xa_lock if @gfp flags permit.
  * Return: 0 if the store succeeded.  -EBUSY if another entry was present.
  * -ENOMEM if memory could not be allocated.
  */
 int __xa_insert(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
 {
     XA_STATE(xas, xa, index);
     void *curr;
 
     if (WARN_ON_ONCE(xa_is_advanced(entry)))
         return -EINVAL;
     if (!entry)
         entry = XA_ZERO_ENTRY;
 
     do {
         curr = xas_load(&xas);
         if (!curr) {
             xas_store(&xas, entry);
             if (xa_track_free(xa))
                 xas_clear_mark(&xas, XA_FREE_MARK);
         } else {
             xas_set_err(&xas, -EBUSY);
         }
     } while (__xas_nomem(&xas, gfp));
 
     return xas_error(&xas);
 }
 EXPORT_SYMBOL(__xa_insert);
 
 #ifdef CONFIG_XARRAY_MULTI
 static void xas_set_range(struct xa_state *xas, unsigned long first,
         unsigned long last)
 {
     unsigned int shift = 0;
     unsigned long sibs = last - first;
     unsigned int offset = XA_CHUNK_MASK;
 
     xas_set(xas, first);
 
     while ((first & XA_CHUNK_MASK) == 0) {
         if (sibs < XA_CHUNK_MASK)
             break;
         if ((sibs == XA_CHUNK_MASK) && (offset < XA_CHUNK_MASK))
             break;
         shift += XA_CHUNK_SHIFT;
         if (offset == XA_CHUNK_MASK)
             offset = sibs & XA_CHUNK_MASK;
         sibs >>= XA_CHUNK_SHIFT;
         first >>= XA_CHUNK_SHIFT;
     }
 
     offset = first & XA_CHUNK_MASK;
     if (offset + sibs > XA_CHUNK_MASK)
         sibs = XA_CHUNK_MASK - offset;
     if ((((first + sibs + 1) << shift) - 1) > last)
         sibs -= 1;
 
     xas->xa_shift = shift;
     xas->xa_sibs = sibs;
 }
 
 /**
  * xa_store_range() - Store this entry at a range of indices in the XArray.
  * @xa: XArray.
  * @first: First index to affect.
  * @last: Last index to affect.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * After this function returns, loads from any index between @first and @last,
  * inclusive will return @entry.
  * Storing into an existing multi-index entry updates the entry of every index.
  * The marks associated with @index are unaffected unless @entry is %NULL.
  *
  * Context: Process context.  Takes and releases the xa_lock.  May sleep
  * if the @gfp flags permit.
  * Return: %NULL on success, xa_err(-EINVAL) if @entry cannot be stored in
  * an XArray, or xa_err(-ENOMEM) if memory allocation failed.
  */
 void *xa_store_range(struct xarray *xa, unsigned long first,
         unsigned long last, void *entry, gfp_t gfp)
 {
     XA_STATE(xas, xa, 0);
 
     if (WARN_ON_ONCE(xa_is_internal(entry)))
         return XA_ERROR(-EINVAL);
     if (last < first)
         return XA_ERROR(-EINVAL);
 
     do {
         xas_lock(&xas);
         if (entry) {
             unsigned int order = BITS_PER_LONG;
             if (last + 1)
                 order = __ffs(last + 1);
             xas_set_order(&xas, last, order);
             xas_create(&xas, true);
             if (xas_error(&xas))
                 goto unlock;
         }
         do {
             xas_set_range(&xas, first, last);
             xas_store(&xas, entry);
             if (xas_error(&xas))
                 goto unlock;
             first += xas_size(&xas);
         } while (first <= last);
 unlock:
         xas_unlock(&xas);
     } while (xas_nomem(&xas, gfp));
 
     return xas_result(&xas, NULL);
 }
 EXPORT_SYMBOL(xa_store_range);
 
 /**
  * xa_get_order() - Get the order of an entry.
  * @xa: XArray.
  * @index: Index of the entry.
  *
  * Return: A number between 0 and 63 indicating the order of the entry.
  */
 int xa_get_order(struct xarray *xa, unsigned long index)
 {
     XA_STATE(xas, xa, index);
     void *entry;
     int order = 0;
 
     rcu_read_lock();
     entry = xas_load(&xas);
 
     if (!entry)
         goto unlock;
 
     if (!xas.xa_node)
         goto unlock;
 
     for (;;) {
         unsigned int slot = xas.xa_offset + (1 << order);
 
         if (slot >= XA_CHUNK_SIZE)
             break;
         if (!xa_is_sibling(xas.xa_node->slots[slot]))
             break;
         order++;
     }
 
     order += xas.xa_node->shift;
 unlock:
     rcu_read_unlock();
 
     return order;
 }
 EXPORT_SYMBOL(xa_get_order);
 #endif /* CONFIG_XARRAY_MULTI */
 
 /**
  * __xa_alloc() - Find somewhere to store this entry in the XArray.
  * @xa: XArray.
  * @id: Pointer to ID.
  * @limit: Range for allocated ID.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * Finds an empty entry in @xa between @limit.min and @limit.max,
  * stores the index into the @id pointer, then stores the entry at
  * that index.  A concurrent lookup will not see an uninitialised @id.
  *
  * Context: Any context.  Expects xa_lock to be held on entry.  May
  * release and reacquire xa_lock if @gfp flags permit.
  * Return: 0 on success, -ENOMEM if memory could not be allocated or
  * -EBUSY if there are no free entries in @limit.
  */
 int __xa_alloc(struct xarray *xa, u32 *id, void *entry,
         struct xa_limit limit, gfp_t gfp)
 {
     XA_STATE(xas, xa, 0);
 
     if (WARN_ON_ONCE(xa_is_advanced(entry)))
         return -EINVAL;
     if (WARN_ON_ONCE(!xa_track_free(xa)))
         return -EINVAL;
 
     if (!entry)
         entry = XA_ZERO_ENTRY;
 
     do {
         xas.xa_index = limit.min;
         xas_find_marked(&xas, limit.max, XA_FREE_MARK);
         if (xas.xa_node == XAS_RESTART)
             xas_set_err(&xas, -EBUSY);
         else
             *id = xas.xa_index;
         xas_store(&xas, entry);
         xas_clear_mark(&xas, XA_FREE_MARK);
     } while (__xas_nomem(&xas, gfp));
 
     return xas_error(&xas);
 }
 EXPORT_SYMBOL(__xa_alloc);
 
 /**
  * __xa_alloc_cyclic() - Find somewhere to store this entry in the XArray.
  * @xa: XArray.
  * @id: Pointer to ID.
  * @entry: New entry.
  * @limit: Range of allocated ID.
  * @next: Pointer to next ID to allocate.
  * @gfp: Memory allocation flags.
  *
  * Finds an empty entry in @xa between @limit.min and @limit.max,
  * stores the index into the @id pointer, then stores the entry at
  * that index.  A concurrent lookup will not see an uninitialised @id.
  * The search for an empty entry will start at @next and will wrap
  * around if necessary.
  *
  * Context: Any context.  Expects xa_lock to be held on entry.  May
  * release and reacquire xa_lock if @gfp flags permit.
  * Return: 0 if the allocation succeeded without wrapping.  1 if the
  * allocation succeeded after wrapping, -ENOMEM if memory could not be
  * allocated or -EBUSY if there are no free entries in @limit.
  */
 int __xa_alloc_cyclic(struct xarray *xa, u32 *id, void *entry,
         struct xa_limit limit, u32 *next, gfp_t gfp)
 {
     u32 min = limit.min;
     int ret;
 
     limit.min = max(min, *next);
     ret = __xa_alloc(xa, id, entry, limit, gfp);
     if ((xa->xa_flags & XA_FLAGS_ALLOC_WRAPPED) && ret == 0) {
         xa->xa_flags &= ~XA_FLAGS_ALLOC_WRAPPED;
         ret = 1;
     }
 
     if (ret < 0 && limit.min > min) {
         limit.min = min;
         ret = __xa_alloc(xa, id, entry, limit, gfp);
         if (ret == 0)
             ret = 1;
     }
 
     if (ret >= 0) {
         *next = *id + 1;
         if (*next == 0)
             xa->xa_flags |= XA_FLAGS_ALLOC_WRAPPED;
     }
     return ret;
 }
 EXPORT_SYMBOL(__xa_alloc_cyclic);
 
 /**
  * __xa_set_mark() - Set this mark on this entry while locked.
  * @xa: XArray.
  * @index: Index of entry.
  * @mark: Mark number.
  *
  * Attempting to set a mark on a %NULL entry does not succeed.
  *
  * Context: Any context.  Expects xa_lock to be held on entry.
  */
 void __xa_set_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
 {
     XA_STATE(xas, xa, index);
     void *entry = xas_load(&xas);
 
     if (entry)
         xas_set_mark(&xas, mark);
 }
 EXPORT_SYMBOL(__xa_set_mark);
 
 /**
  * __xa_clear_mark() - Clear this mark on this entry while locked.
  * @xa: XArray.
  * @index: Index of entry.
  * @mark: Mark number.
  *
  * Context: Any context.  Expects xa_lock to be held on entry.
  */
 void __xa_clear_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
 {
     XA_STATE(xas, xa, index);
     void *entry = xas_load(&xas);
 
     if (entry)
         xas_clear_mark(&xas, mark);
 }
 EXPORT_SYMBOL(__xa_clear_mark);
 
 /**
  * xa_get_mark() - Inquire whether this mark is set on this entry.
  * @xa: XArray.
  * @index: Index of entry.
  * @mark: Mark number.
  *
  * This function uses the RCU read lock, so the result may be out of date
  * by the time it returns.  If you need the result to be stable, use a lock.
  *
  * Context: Any context.  Takes and releases the RCU lock.
  * Return: True if the entry at @index has this mark set, false if it doesn't.
  */
 bool xa_get_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
 {
     XA_STATE(xas, xa, index);
     void *entry;
 
     rcu_read_lock();
     entry = xas_start(&xas);
     while (xas_get_mark(&xas, mark)) {
         if (!xa_is_node(entry))
             goto found;
         entry = xas_descend(&xas, xa_to_node(entry));
     }
     rcu_read_unlock();
     return false;
  found:
     rcu_read_unlock();
     return true;
 }
 EXPORT_SYMBOL(xa_get_mark);
 
 /**
  * xa_set_mark() - Set this mark on this entry.
  * @xa: XArray.
  * @index: Index of entry.
  * @mark: Mark number.
  *
  * Attempting to set a mark on a %NULL entry does not succeed.
  *
  * Context: Process context.  Takes and releases the xa_lock.
  */
 void xa_set_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
 {
     xa_lock(xa);
     __xa_set_mark(xa, index, mark);
     xa_unlock(xa);
 }
 EXPORT_SYMBOL(xa_set_mark);
 
 /**
  * xa_clear_mark() - Clear this mark on this entry.
  * @xa: XArray.
  * @index: Index of entry.
  * @mark: Mark number.
  *
  * Clearing a mark always succeeds.
  *
  * Context: Process context.  Takes and releases the xa_lock.
  */
 void xa_clear_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
 {
     xa_lock(xa);
     __xa_clear_mark(xa, index, mark);
     xa_unlock(xa);
 }
 EXPORT_SYMBOL(xa_clear_mark);
 
 /**
  * xa_find() - Search the XArray for an entry.
  * @xa: XArray.
  * @indexp: Pointer to an index.
  * @max: Maximum index to search to.
  * @filter: Selection criterion.
  *
  * Finds the entry in @xa which matches the @filter, and has the lowest
  * index that is at least @indexp and no more than @max.
  * If an entry is found, @indexp is updated to be the index of the entry.
  * This function is protected by the RCU read lock, so it may not find
  * entries which are being simultaneously added.  It will not return an
  * %XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
  *
  * Context: Any context.  Takes and releases the RCU lock.
  * Return: The entry, if found, otherwise %NULL.
  */
 void *xa_find(struct xarray *xa, unsigned long *indexp,
             unsigned long max, xa_mark_t filter)
 {
     XA_STATE(xas, xa, *indexp);
     void *entry;
 
     rcu_read_lock();
     do {
         if ((__force unsigned int)filter < XA_MAX_MARKS)
             entry = xas_find_marked(&xas, max, filter);
         else
             entry = xas_find(&xas, max);
     } while (xas_retry(&xas, entry));
     rcu_read_unlock();
 
     if (entry)
         *indexp = xas.xa_index;
     return entry;
 }
 EXPORT_SYMBOL(xa_find);
 
 static bool xas_sibling(struct xa_state *xas)
 {
     struct xa_node *node = xas->xa_node;
     unsigned long mask;
 
     if (!IS_ENABLED(CONFIG_XARRAY_MULTI) || !node)
         return false;
     mask = (XA_CHUNK_SIZE << node->shift) - 1;
     return (xas->xa_index & mask) >
         ((unsigned long)xas->xa_offset << node->shift);
 }
 
 /**
  * xa_find_after() - Search the XArray for a present entry.
  * @xa: XArray.
  * @indexp: Pointer to an index.
  * @max: Maximum index to search to.
  * @filter: Selection criterion.
  *
  * Finds the entry in @xa which matches the @filter and has the lowest
  * index that is above @indexp and no more than @max.
  * If an entry is found, @indexp is updated to be the index of the entry.
  * This function is protected by the RCU read lock, so it may miss entries
  * which are being simultaneously added.  It will not return an
  * %XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
  *
  * Context: Any context.  Takes and releases the RCU lock.
  * Return: The pointer, if found, otherwise %NULL.
  */
 void *xa_find_after(struct xarray *xa, unsigned long *indexp,
             unsigned long max, xa_mark_t filter)
 {
     XA_STATE(xas, xa, *indexp + 1);
     void *entry;
 
     if (xas.xa_index == 0)
         return NULL;
 
     rcu_read_lock();
     for (;;) {
         if ((__force unsigned int)filter < XA_MAX_MARKS)
             entry = xas_find_marked(&xas, max, filter);
         else
             entry = xas_find(&xas, max);
 
         if (xas_invalid(&xas))
             break;
         if (xas_sibling(&xas))
             continue;
         if (!xas_retry(&xas, entry))
             break;
     }
     rcu_read_unlock();
 
     if (entry)
         *indexp = xas.xa_index;
     return entry;
 }
 EXPORT_SYMBOL(xa_find_after);
 
 static unsigned int xas_extract_present(struct xa_state *xas, void **dst,
             unsigned long max, unsigned int n)
 {
     void *entry;
     unsigned int i = 0;
 
     rcu_read_lock();
     xas_for_each(xas, entry, max) {
         if (xas_retry(xas, entry))
             continue;
         dst[i++] = entry;
         if (i == n)
             break;
     }
     rcu_read_unlock();
 
     return i;
 }
 
 static unsigned int xas_extract_marked(struct xa_state *xas, void **dst,
             unsigned long max, unsigned int n, xa_mark_t mark)
 {
     void *entry;
     unsigned int i = 0;
 
     rcu_read_lock();
     xas_for_each_marked(xas, entry, max, mark) {
         if (xas_retry(xas, entry))
             continue;
         dst[i++] = entry;
         if (i == n)
             break;
     }
     rcu_read_unlock();
 
     return i;
 }
 
 /**
  * xa_extract() - Copy selected entries from the XArray into a normal array.
  * @xa: The source XArray to copy from.
  * @dst: The buffer to copy entries into.
  * @start: The first index in the XArray eligible to be selected.
  * @max: The last index in the XArray eligible to be selected.
  * @n: The maximum number of entries to copy.
  * @filter: Selection criterion.
  *
  * Copies up to @n entries that match @filter from the XArray.  The
  * copied entries will have indices between @start and @max, inclusive.
  *
  * The @filter may be an XArray mark value, in which case entries which are
  * marked with that mark will be copied.  It may also be %XA_PRESENT, in
  * which case all entries which are not %NULL will be copied.
  *
  * The entries returned may not represent a snapshot of the XArray at a
  * moment in time.  For example, if another thread stores to index 5, then
  * index 10, calling xa_extract() may return the old contents of index 5
  * and the new contents of index 10.  Indices not modified while this
  * function is running will not be skipped.
  *
  * If you need stronger guarantees, holding the xa_lock across calls to this
  * function will prevent concurrent modification.
  *
  * Context: Any context.  Takes and releases the RCU lock.
  * Return: The number of entries copied.
  */
 unsigned int xa_extract(struct xarray *xa, void **dst, unsigned long start,
             unsigned long max, unsigned int n, xa_mark_t filter)
 {
     XA_STATE(xas, xa, start);
 
     if (!n)
         return 0;
 
     if ((__force unsigned int)filter < XA_MAX_MARKS)
         return xas_extract_marked(&xas, dst, max, n, filter);
     return xas_extract_present(&xas, dst, max, n);
 }
 EXPORT_SYMBOL(xa_extract);
 
 /**
  * xa_delete_node() - Private interface for workingset code.
  * @node: Node to be removed from the tree.
  * @update: Function to call to update ancestor nodes.
  *
  * Context: xa_lock must be held on entry and will not be released.
  */
 void xa_delete_node(struct xa_node *node, xa_update_node_t update)
 {
     struct xa_state xas = {
         .xa = node->array,
         .xa_index = (unsigned long)node->offset <<
                 (node->shift + XA_CHUNK_SHIFT),
         .xa_shift = node->shift + XA_CHUNK_SHIFT,
         .xa_offset = node->offset,
         .xa_node = xa_parent_locked(node->array, node),
         .xa_update = update,
     };
 
     xas_store(&xas, NULL);
 }
 EXPORT_SYMBOL_GPL(xa_delete_node);  /* For the benefit of the test suite */
 
 /**
  * xa_destroy() - Free all internal data structures.
  * @xa: XArray.
  *
  * After calling this function, the XArray is empty and has freed all memory
  * allocated for its internal data structures.  You are responsible for
  * freeing the objects referenced by the XArray.
  *
  * Context: Any context.  Takes and releases the xa_lock, interrupt-safe.
  */
 void xa_destroy(struct xarray *xa)
 {
     XA_STATE(xas, xa, 0);
     unsigned long flags;
     void *entry;
 
     xas.xa_node = NULL;
     xas_lock_irqsave(&xas, flags);
     entry = xa_head_locked(xa);
     RCU_INIT_POINTER(xa->xa_head, NULL);
     xas_init_marks(&xas);
     if (xa_zero_busy(xa))
         xa_mark_clear(xa, XA_FREE_MARK);
     /* lockdep checks we're still holding the lock in xas_free_nodes() */
     if (xa_is_node(entry))
         xas_free_nodes(&xas, xa_to_node(entry));
     xas_unlock_irqrestore(&xas, flags);
 }
 EXPORT_SYMBOL(xa_destroy);
 
 #ifdef XA_DEBUG
 void xa_dump_node(const struct xa_node *node)
 {
     unsigned i, j;
 
     if (!node)
         return;
     if ((unsigned long)node & 3) {
         pr_cont("node %px\n", node);
         return;
     }
 
     pr_cont("node %px %s %d parent %px shift %d count %d values %d "
         "array %px list %px %px marks",
         node, node->parent ? "offset" : "max", node->offset,
         node->parent, node->shift, node->count, node->nr_values,
         node->array, node->private_list.prev, node->private_list.next);
     for (i = 0; i < XA_MAX_MARKS; i++)
         for (j = 0; j < XA_MARK_LONGS; j++)
             pr_cont(" %lx", node->marks[i][j]);
     pr_cont("\n");
 }
 
 void xa_dump_index(unsigned long index, unsigned int shift)
 {
     if (!shift)
         pr_info("%lu: ", index);
     else if (shift >= BITS_PER_LONG)
         pr_info("0-%lu: ", ~0UL);
     else
         pr_info("%lu-%lu: ", index, index | ((1UL << shift) - 1));
 }
 
 void xa_dump_entry(const void *entry, unsigned long index, unsigned long shift)
 {
     if (!entry)
         return;
 
     xa_dump_index(index, shift);
 
     if (xa_is_node(entry)) {
         if (shift == 0) {
             pr_cont("%px\n", entry);
         } else {
             unsigned long i;
             struct xa_node *node = xa_to_node(entry);
             xa_dump_node(node);
             for (i = 0; i < XA_CHUNK_SIZE; i++)
                 xa_dump_entry(node->slots[i],
                       index + (i << node->shift), node->shift);
         }
     } else if (xa_is_value(entry))
         pr_cont("value %ld (0x%lx) [%px]\n", xa_to_value(entry),
                         xa_to_value(entry), entry);
     else if (!xa_is_internal(entry))
         pr_cont("%px\n", entry);
     else if (xa_is_retry(entry))
         pr_cont("retry (%ld)\n", xa_to_internal(entry));
     else if (xa_is_sibling(entry))
         pr_cont("sibling (slot %ld)\n", xa_to_sibling(entry));
     else if (xa_is_zero(entry))
         pr_cont("zero (%ld)\n", xa_to_internal(entry));
     else
         pr_cont("UNKNOWN ENTRY (%px)\n", entry);
 }
 
 void xa_dump(const struct xarray *xa)
 {
     void *entry = xa->xa_head;
     unsigned int shift = 0;
 
     pr_info("xarray: %px head %px flags %x marks %d %d %d\n", xa, entry,
             xa->xa_flags, xa_marked(xa, XA_MARK_0),
             xa_marked(xa, XA_MARK_1), xa_marked(xa, XA_MARK_2));
     if (xa_is_node(entry))
         shift = xa_to_node(entry)->shift + XA_CHUNK_SHIFT;
     xa_dump_entry(entry, 0, shift);
 }
 #endif

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