Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 795 insertions, 0 deletions

diff --git a/lib/btree.c b/lib/btree.c
new file mode 100644
index 000000000..9c80c0c7b
--- /dev/null
+++ b/lib/btree.c
@@ -0,0 +1,795 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * lib/btree.c	- Simple In-memory B+Tree
+ *
+ * Copyright (c) 2007-2008 Joern Engel <joern@purestorage.com>
+ * Bits and pieces stolen from Peter Zijlstra's code, which is
+ * Copyright 2007, Red Hat Inc. Peter Zijlstra
+ *
+ * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch
+ *
+ * A relatively simple B+Tree implementation.  I have written it as a learning
+ * exercise to understand how B+Trees work.  Turned out to be useful as well.
+ *
+ * B+Trees can be used similar to Linux radix trees (which don't have anything
+ * in common with textbook radix trees, beware).  Prerequisite for them working
+ * well is that access to a random tree node is much faster than a large number
+ * of operations within each node.
+ *
+ * Disks have fulfilled the prerequisite for a long time.  More recently DRAM
+ * has gained similar properties, as memory access times, when measured in cpu
+ * cycles, have increased.  Cacheline sizes have increased as well, which also
+ * helps B+Trees.
+ *
+ * Compared to radix trees, B+Trees are more efficient when dealing with a
+ * sparsely populated address space.  Between 25% and 50% of the memory is
+ * occupied with valid pointers.  When densely populated, radix trees contain
+ * ~98% pointers - hard to beat.  Very sparse radix trees contain only ~2%
+ * pointers.
+ *
+ * This particular implementation stores pointers identified by a long value.
+ * Storing NULL pointers is illegal, lookup will return NULL when no entry
+ * was found.
+ *
+ * A tricks was used that is not commonly found in textbooks.  The lowest
+ * values are to the right, not to the left.  All used slots within a node
+ * are on the left, all unused slots contain NUL values.  Most operations
+ * simply loop once over all slots and terminate on the first NUL.
+ */
+
+#include <linux/btree.h>
+#include <linux/cache.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+#define NODESIZE MAX(L1_CACHE_BYTES, 128)
+
+struct btree_geo {
+	int keylen;
+	int no_pairs;
+	int no_longs;
+};
+
+struct btree_geo btree_geo32 = {
+	.keylen = 1,
+	.no_pairs = NODESIZE / sizeof(long) / 2,
+	.no_longs = NODESIZE / sizeof(long) / 2,
+};
+EXPORT_SYMBOL_GPL(btree_geo32);
+
+#define LONG_PER_U64 (64 / BITS_PER_LONG)
+struct btree_geo btree_geo64 = {
+	.keylen = LONG_PER_U64,
+	.no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64),
+	.no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)),
+};
+EXPORT_SYMBOL_GPL(btree_geo64);
+
+struct btree_geo btree_geo128 = {
+	.keylen = 2 * LONG_PER_U64,
+	.no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64),
+	.no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)),
+};
+EXPORT_SYMBOL_GPL(btree_geo128);
+
+#define MAX_KEYLEN	(2 * LONG_PER_U64)
+
+static struct kmem_cache *btree_cachep;
+
+void *btree_alloc(gfp_t gfp_mask, void *pool_data)
+{
+	return kmem_cache_alloc(btree_cachep, gfp_mask);
+}
+EXPORT_SYMBOL_GPL(btree_alloc);
+
+void btree_free(void *element, void *pool_data)
+{
+	kmem_cache_free(btree_cachep, element);
+}
+EXPORT_SYMBOL_GPL(btree_free);
+
+static unsigned long *btree_node_alloc(struct btree_head *head, gfp_t gfp)
+{
+	unsigned long *node;
+
+	node = mempool_alloc(head->mempool, gfp);
+	if (likely(node))
+		memset(node, 0, NODESIZE);
+	return node;
+}
+
+static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n)
+{
+	size_t i;
+
+	for (i = 0; i < n; i++) {
+		if (l1[i] < l2[i])
+			return -1;
+		if (l1[i] > l2[i])
+			return 1;
+	}
+	return 0;
+}
+
+static unsigned long *longcpy(unsigned long *dest, const unsigned long *src,
+		size_t n)
+{
+	size_t i;
+
+	for (i = 0; i < n; i++)
+		dest[i] = src[i];
+	return dest;
+}
+
+static unsigned long *longset(unsigned long *s, unsigned long c, size_t n)
+{
+	size_t i;
+
+	for (i = 0; i < n; i++)
+		s[i] = c;
+	return s;
+}
+
+static void dec_key(struct btree_geo *geo, unsigned long *key)
+{
+	unsigned long val;
+	int i;
+
+	for (i = geo->keylen - 1; i >= 0; i--) {
+		val = key[i];
+		key[i] = val - 1;
+		if (val)
+			break;
+	}
+}
+
+static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n)
+{
+	return &node[n * geo->keylen];
+}
+
+static void *bval(struct btree_geo *geo, unsigned long *node, int n)
+{
+	return (void *)node[geo->no_longs + n];
+}
+
+static void setkey(struct btree_geo *geo, unsigned long *node, int n,
+		   unsigned long *key)
+{
+	longcpy(bkey(geo, node, n), key, geo->keylen);
+}
+
+static void setval(struct btree_geo *geo, unsigned long *node, int n,
+		   void *val)
+{
+	node[geo->no_longs + n] = (unsigned long) val;
+}
+
+static void clearpair(struct btree_geo *geo, unsigned long *node, int n)
+{
+	longset(bkey(geo, node, n), 0, geo->keylen);
+	node[geo->no_longs + n] = 0;
+}
+
+static inline void __btree_init(struct btree_head *head)
+{
+	head->node = NULL;
+	head->height = 0;
+}
+
+void btree_init_mempool(struct btree_head *head, mempool_t *mempool)
+{
+	__btree_init(head);
+	head->mempool = mempool;
+}
+EXPORT_SYMBOL_GPL(btree_init_mempool);
+
+int btree_init(struct btree_head *head)
+{
+	__btree_init(head);
+	head->mempool = mempool_create(0, btree_alloc, btree_free, NULL);
+	if (!head->mempool)
+		return -ENOMEM;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(btree_init);
+
+void btree_destroy(struct btree_head *head)
+{
+	mempool_free(head->node, head->mempool);
+	mempool_destroy(head->mempool);
+	head->mempool = NULL;
+}
+EXPORT_SYMBOL_GPL(btree_destroy);
+
+void *btree_last(struct btree_head *head, struct btree_geo *geo,
+		 unsigned long *key)
+{
+	int height = head->height;
+	unsigned long *node = head->node;
+
+	if (height == 0)
+		return NULL;
+
+	for ( ; height > 1; height--)
+		node = bval(geo, node, 0);
+
+	longcpy(key, bkey(geo, node, 0), geo->keylen);
+	return bval(geo, node, 0);
+}
+EXPORT_SYMBOL_GPL(btree_last);
+
+static int keycmp(struct btree_geo *geo, unsigned long *node, int pos,
+		  unsigned long *key)
+{
+	return longcmp(bkey(geo, node, pos), key, geo->keylen);
+}
+
+static int keyzero(struct btree_geo *geo, unsigned long *key)
+{
+	int i;
+
+	for (i = 0; i < geo->keylen; i++)
+		if (key[i])
+			return 0;
+
+	return 1;
+}
+
+static void *btree_lookup_node(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key)
+{
+	int i, height = head->height;
+	unsigned long *node = head->node;
+
+	if (height == 0)
+		return NULL;
+
+	for ( ; height > 1; height--) {
+		for (i = 0; i < geo->no_pairs; i++)
+			if (keycmp(geo, node, i, key) <= 0)
+				break;
+		if (i == geo->no_pairs)
+			return NULL;
+		node = bval(geo, node, i);
+		if (!node)
+			return NULL;
+	}
+	return node;
+}
+
+void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key)
+{
+	int i;
+	unsigned long *node;
+
+	node = btree_lookup_node(head, geo, key);
+	if (!node)
+		return NULL;
+
+	for (i = 0; i < geo->no_pairs; i++)
+		if (keycmp(geo, node, i, key) == 0)
+			return bval(geo, node, i);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(btree_lookup);
+
+int btree_update(struct btree_head *head, struct btree_geo *geo,
+		 unsigned long *key, void *val)
+{
+	int i;
+	unsigned long *node;
+
+	node = btree_lookup_node(head, geo, key);
+	if (!node)
+		return -ENOENT;
+
+	for (i = 0; i < geo->no_pairs; i++)
+		if (keycmp(geo, node, i, key) == 0) {
+			setval(geo, node, i, val);
+			return 0;
+		}
+	return -ENOENT;
+}
+EXPORT_SYMBOL_GPL(btree_update);
+
+/*
+ * Usually this function is quite similar to normal lookup.  But the key of
+ * a parent node may be smaller than the smallest key of all its siblings.
+ * In such a case we cannot just return NULL, as we have only proven that no
+ * key smaller than __key, but larger than this parent key exists.
+ * So we set __key to the parent key and retry.  We have to use the smallest
+ * such parent key, which is the last parent key we encountered.
+ */
+void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
+		     unsigned long *__key)
+{
+	int i, height;
+	unsigned long *node, *oldnode;
+	unsigned long *retry_key = NULL, key[MAX_KEYLEN];
+
+	if (keyzero(geo, __key))
+		return NULL;
+
+	if (head->height == 0)
+		return NULL;
+	longcpy(key, __key, geo->keylen);
+retry:
+	dec_key(geo, key);
+
+	node = head->node;
+	for (height = head->height ; height > 1; height--) {
+		for (i = 0; i < geo->no_pairs; i++)
+			if (keycmp(geo, node, i, key) <= 0)
+				break;
+		if (i == geo->no_pairs)
+			goto miss;
+		oldnode = node;
+		node = bval(geo, node, i);
+		if (!node)
+			goto miss;
+		retry_key = bkey(geo, oldnode, i);
+	}
+
+	if (!node)
+		goto miss;
+
+	for (i = 0; i < geo->no_pairs; i++) {
+		if (keycmp(geo, node, i, key) <= 0) {
+			if (bval(geo, node, i)) {
+				longcpy(__key, bkey(geo, node, i), geo->keylen);
+				return bval(geo, node, i);
+			} else
+				goto miss;
+		}
+	}
+miss:
+	if (retry_key) {
+		longcpy(key, retry_key, geo->keylen);
+		retry_key = NULL;
+		goto retry;
+	}
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(btree_get_prev);
+
+static int getpos(struct btree_geo *geo, unsigned long *node,
+		unsigned long *key)
+{
+	int i;
+
+	for (i = 0; i < geo->no_pairs; i++) {
+		if (keycmp(geo, node, i, key) <= 0)
+			break;
+	}
+	return i;
+}
+
+static int getfill(struct btree_geo *geo, unsigned long *node, int start)
+{
+	int i;
+
+	for (i = start; i < geo->no_pairs; i++)
+		if (!bval(geo, node, i))
+			break;
+	return i;
+}
+
+/*
+ * locate the correct leaf node in the btree
+ */
+static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, int level)
+{
+	unsigned long *node = head->node;
+	int i, height;
+
+	for (height = head->height; height > level; height--) {
+		for (i = 0; i < geo->no_pairs; i++)
+			if (keycmp(geo, node, i, key) <= 0)
+				break;
+
+		if ((i == geo->no_pairs) || !bval(geo, node, i)) {
+			/* right-most key is too large, update it */
+			/* FIXME: If the right-most key on higher levels is
+			 * always zero, this wouldn't be necessary. */
+			i--;
+			setkey(geo, node, i, key);
+		}
+		BUG_ON(i < 0);
+		node = bval(geo, node, i);
+	}
+	BUG_ON(!node);
+	return node;
+}
+
+static int btree_grow(struct btree_head *head, struct btree_geo *geo,
+		      gfp_t gfp)
+{
+	unsigned long *node;
+	int fill;
+
+	node = btree_node_alloc(head, gfp);
+	if (!node)
+		return -ENOMEM;
+	if (head->node) {
+		fill = getfill(geo, head->node, 0);
+		setkey(geo, node, 0, bkey(geo, head->node, fill - 1));
+		setval(geo, node, 0, head->node);
+	}
+	head->node = node;
+	head->height++;
+	return 0;
+}
+
+static void btree_shrink(struct btree_head *head, struct btree_geo *geo)
+{
+	unsigned long *node;
+	int fill;
+
+	if (head->height <= 1)
+		return;
+
+	node = head->node;
+	fill = getfill(geo, node, 0);
+	BUG_ON(fill > 1);
+	head->node = bval(geo, node, 0);
+	head->height--;
+	mempool_free(node, head->mempool);
+}
+
+static int btree_insert_level(struct btree_head *head, struct btree_geo *geo,
+			      unsigned long *key, void *val, int level,
+			      gfp_t gfp)
+{
+	unsigned long *node;
+	int i, pos, fill, err;
+
+	BUG_ON(!val);
+	if (head->height < level) {
+		err = btree_grow(head, geo, gfp);
+		if (err)
+			return err;
+	}
+
+retry:
+	node = find_level(head, geo, key, level);
+	pos = getpos(geo, node, key);
+	fill = getfill(geo, node, pos);
+	/* two identical keys are not allowed */
+	BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0);
+
+	if (fill == geo->no_pairs) {
+		/* need to split node */
+		unsigned long *new;
+
+		new = btree_node_alloc(head, gfp);
+		if (!new)
+			return -ENOMEM;
+		err = btree_insert_level(head, geo,
+				bkey(geo, node, fill / 2 - 1),
+				new, level + 1, gfp);
+		if (err) {
+			mempool_free(new, head->mempool);
+			return err;
+		}
+		for (i = 0; i < fill / 2; i++) {
+			setkey(geo, new, i, bkey(geo, node, i));
+			setval(geo, new, i, bval(geo, node, i));
+			setkey(geo, node, i, bkey(geo, node, i + fill / 2));
+			setval(geo, node, i, bval(geo, node, i + fill / 2));
+			clearpair(geo, node, i + fill / 2);
+		}
+		if (fill & 1) {
+			setkey(geo, node, i, bkey(geo, node, fill - 1));
+			setval(geo, node, i, bval(geo, node, fill - 1));
+			clearpair(geo, node, fill - 1);
+		}
+		goto retry;
+	}
+	BUG_ON(fill >= geo->no_pairs);
+
+	/* shift and insert */
+	for (i = fill; i > pos; i--) {
+		setkey(geo, node, i, bkey(geo, node, i - 1));
+		setval(geo, node, i, bval(geo, node, i - 1));
+	}
+	setkey(geo, node, pos, key);
+	setval(geo, node, pos, val);
+
+	return 0;
+}
+
+int btree_insert(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, void *val, gfp_t gfp)
+{
+	BUG_ON(!val);
+	return btree_insert_level(head, geo, key, val, 1, gfp);
+}
+EXPORT_SYMBOL_GPL(btree_insert);
+
+static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, int level);
+static void merge(struct btree_head *head, struct btree_geo *geo, int level,
+		unsigned long *left, int lfill,
+		unsigned long *right, int rfill,
+		unsigned long *parent, int lpos)
+{
+	int i;
+
+	for (i = 0; i < rfill; i++) {
+		/* Move all keys to the left */
+		setkey(geo, left, lfill + i, bkey(geo, right, i));
+		setval(geo, left, lfill + i, bval(geo, right, i));
+	}
+	/* Exchange left and right child in parent */
+	setval(geo, parent, lpos, right);
+	setval(geo, parent, lpos + 1, left);
+	/* Remove left (formerly right) child from parent */
+	btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
+	mempool_free(right, head->mempool);
+}
+
+static void rebalance(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, int level, unsigned long *child, int fill)
+{
+	unsigned long *parent, *left = NULL, *right = NULL;
+	int i, no_left, no_right;
+
+	if (fill == 0) {
+		/* Because we don't steal entries from a neighbour, this case
+		 * can happen.  Parent node contains a single child, this
+		 * node, so merging with a sibling never happens.
+		 */
+		btree_remove_level(head, geo, key, level + 1);
+		mempool_free(child, head->mempool);
+		return;
+	}
+
+	parent = find_level(head, geo, key, level + 1);
+	i = getpos(geo, parent, key);
+	BUG_ON(bval(geo, parent, i) != child);
+
+	if (i > 0) {
+		left = bval(geo, parent, i - 1);
+		no_left = getfill(geo, left, 0);
+		if (fill + no_left <= geo->no_pairs) {
+			merge(head, geo, level,
+					left, no_left,
+					child, fill,
+					parent, i - 1);
+			return;
+		}
+	}
+	if (i + 1 < getfill(geo, parent, i)) {
+		right = bval(geo, parent, i + 1);
+		no_right = getfill(geo, right, 0);
+		if (fill + no_right <= geo->no_pairs) {
+			merge(head, geo, level,
+					child, fill,
+					right, no_right,
+					parent, i);
+			return;
+		}
+	}
+	/*
+	 * We could also try to steal one entry from the left or right
+	 * neighbor.  By not doing so we changed the invariant from
+	 * "all nodes are at least half full" to "no two neighboring
+	 * nodes can be merged".  Which means that the average fill of
+	 * all nodes is still half or better.
+	 */
+}
+
+static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, int level)
+{
+	unsigned long *node;
+	int i, pos, fill;
+	void *ret;
+
+	if (level > head->height) {
+		/* we recursed all the way up */
+		head->height = 0;
+		head->node = NULL;
+		return NULL;
+	}
+
+	node = find_level(head, geo, key, level);
+	pos = getpos(geo, node, key);
+	fill = getfill(geo, node, pos);
+	if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
+		return NULL;
+	ret = bval(geo, node, pos);
+
+	/* remove and shift */
+	for (i = pos; i < fill - 1; i++) {
+		setkey(geo, node, i, bkey(geo, node, i + 1));
+		setval(geo, node, i, bval(geo, node, i + 1));
+	}
+	clearpair(geo, node, fill - 1);
+
+	if (fill - 1 < geo->no_pairs / 2) {
+		if (level < head->height)
+			rebalance(head, geo, key, level, node, fill - 1);
+		else if (fill - 1 == 1)
+			btree_shrink(head, geo);
+	}
+
+	return ret;
+}
+
+void *btree_remove(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key)
+{
+	if (head->height == 0)
+		return NULL;
+
+	return btree_remove_level(head, geo, key, 1);
+}
+EXPORT_SYMBOL_GPL(btree_remove);
+
+int btree_merge(struct btree_head *target, struct btree_head *victim,
+		struct btree_geo *geo, gfp_t gfp)
+{
+	unsigned long key[MAX_KEYLEN];
+	unsigned long dup[MAX_KEYLEN];
+	void *val;
+	int err;
+
+	BUG_ON(target == victim);
+
+	if (!(target->node)) {
+		/* target is empty, just copy fields over */
+		target->node = victim->node;
+		target->height = victim->height;
+		__btree_init(victim);
+		return 0;
+	}
+
+	/* TODO: This needs some optimizations.  Currently we do three tree
+	 * walks to remove a single object from the victim.
+	 */
+	for (;;) {
+		val = btree_last(victim, geo, key);
+		if (!val)
+			break;
+		err = btree_insert(target, geo, key, val, gfp);
+		if (err)
+			return err;
+		/* We must make a copy of the key, as the original will get
+		 * mangled inside btree_remove. */
+		longcpy(dup, key, geo->keylen);
+		btree_remove(victim, geo, dup);
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(btree_merge);
+
+static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
+			       unsigned long *node, unsigned long opaque,
+			       void (*func)(void *elem, unsigned long opaque,
+					    unsigned long *key, size_t index,
+					    void *func2),
+			       void *func2, int reap, int height, size_t count)
+{
+	int i;
+	unsigned long *child;
+
+	for (i = 0; i < geo->no_pairs; i++) {
+		child = bval(geo, node, i);
+		if (!child)
+			break;
+		if (height > 1)
+			count = __btree_for_each(head, geo, child, opaque,
+					func, func2, reap, height - 1, count);
+		else
+			func(child, opaque, bkey(geo, node, i), count++,
+					func2);
+	}
+	if (reap)
+		mempool_free(node, head->mempool);
+	return count;
+}
+
+static void empty(void *elem, unsigned long opaque, unsigned long *key,
+		  size_t index, void *func2)
+{
+}
+
+void visitorl(void *elem, unsigned long opaque, unsigned long *key,
+	      size_t index, void *__func)
+{
+	visitorl_t func = __func;
+
+	func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitorl);
+
+void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
+	       size_t index, void *__func)
+{
+	visitor32_t func = __func;
+	u32 *key = (void *)__key;
+
+	func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitor32);
+
+void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
+	       size_t index, void *__func)
+{
+	visitor64_t func = __func;
+	u64 *key = (void *)__key;
+
+	func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitor64);
+
+void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
+		size_t index, void *__func)
+{
+	visitor128_t func = __func;
+	u64 *key = (void *)__key;
+
+	func(elem, opaque, key[0], key[1], index);
+}
+EXPORT_SYMBOL_GPL(visitor128);
+
+size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
+		     unsigned long opaque,
+		     void (*func)(void *elem, unsigned long opaque,
+		     		  unsigned long *key,
+		     		  size_t index, void *func2),
+		     void *func2)
+{
+	size_t count = 0;
+
+	if (!func2)
+		func = empty;
+	if (head->node)
+		count = __btree_for_each(head, geo, head->node, opaque, func,
+				func2, 0, head->height, 0);
+	return count;
+}
+EXPORT_SYMBOL_GPL(btree_visitor);
+
+size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
+			  unsigned long opaque,
+			  void (*func)(void *elem, unsigned long opaque,
+				       unsigned long *key,
+				       size_t index, void *func2),
+			  void *func2)
+{
+	size_t count = 0;
+
+	if (!func2)
+		func = empty;
+	if (head->node)
+		count = __btree_for_each(head, geo, head->node, opaque, func,
+				func2, 1, head->height, 0);
+	__btree_init(head);
+	return count;
+}
+EXPORT_SYMBOL_GPL(btree_grim_visitor);
+
+static int __init btree_module_init(void)
+{
+	btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
+			SLAB_HWCACHE_ALIGN, NULL);
+	return 0;
+}
+
+static void __exit btree_module_exit(void)
+{
+	kmem_cache_destroy(btree_cachep);
+}
+
+/* If core code starts using btree, initialization should happen even earlier */
+module_init(btree_module_init);
+module_exit(btree_module_exit);
+
+MODULE_AUTHOR("Joern Engel <joern@logfs.org>");
+MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>");