btrfs: turn fs_info member buffer_radix into XArray

… named 'extent_buffers'. Also adjust all usages of this object to use
the XArray API, which greatly simplifies the code as it takes care of
locking and is generally easier to use and understand, providing
notionally simpler array semantics.

Also perform some light refactoring.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Gabriel Niebler <gniebler@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -994,10 +994,10 @@ struct btrfs_fs_info {
 
 	struct btrfs_delayed_root *delayed_root;
 
-	/* Extent buffer radix tree */
+	/* Extent buffer xarray */
 	spinlock_t buffer_lock;
 	/* Entries are eb->start / sectorsize */
-	struct radix_tree_root buffer_radix;
+	struct xarray extent_buffers;
 
 	/* next backup root to be overwritten */
 	int backup_root_index;

fs/btrfs/disk-io.c

@@ -486,7 +486,7 @@ static int csum_dirty_subpage_buffers(struct btrfs_fs_info *fs_info,
 		uptodate = btrfs_subpage_test_uptodate(fs_info, page, cur,
 						       fs_info->nodesize);
 
-		/* A dirty eb shouldn't disappear from buffer_radix */
+		/* A dirty eb shouldn't disappear from extent_buffers */
 		if (WARN_ON(!eb))
 			return -EUCLEAN;
 
@@ -3151,7 +3151,7 @@ static int __cold init_tree_roots(struct btrfs_fs_info *fs_info)
 void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
 {
 	INIT_RADIX_TREE(&fs_info->fs_roots_radix, GFP_ATOMIC);
-	INIT_RADIX_TREE(&fs_info->buffer_radix, GFP_ATOMIC);
+	xa_init_flags(&fs_info->extent_buffers, GFP_ATOMIC);
 	INIT_LIST_HEAD(&fs_info->trans_list);
 	INIT_LIST_HEAD(&fs_info->dead_roots);
 	INIT_LIST_HEAD(&fs_info->delayed_iputs);

fs/btrfs/extent_io.c

@@ -2965,7 +2965,7 @@ static void begin_page_read(struct btrfs_fs_info *fs_info, struct page *page)
 }
 
 /*
- * Find extent buffer for a givne bytenr.
+ * Find extent buffer for a given bytenr.
  *
  * This is for end_bio_extent_readpage(), thus we can't do any unsafe locking
  * in endio context.
@@ -2984,11 +2984,9 @@ static struct extent_buffer *find_extent_buffer_readpage(
 		return (struct extent_buffer *)page->private;
 	}
 
-	/* For subpage case, we need to lookup buffer radix tree */
-	rcu_read_lock();
-	eb = radix_tree_lookup(&fs_info->buffer_radix,
+	/* For subpage case, we need to lookup extent buffer xarray */
+	eb = xa_load(&fs_info->extent_buffers,
 		     bytenr >> fs_info->sectorsize_bits);
-	rcu_read_unlock();
 	ASSERT(eb);
 	return eb;
 }
@@ -4447,7 +4445,7 @@ static struct extent_buffer *find_extent_buffer_nolock(
 	struct extent_buffer *eb;
 
 	rcu_read_lock();
-	eb = radix_tree_lookup(&fs_info->buffer_radix,
+	eb = xa_load(&fs_info->extent_buffers,
 		     start >> fs_info->sectorsize_bits);
 	if (eb && atomic_inc_not_zero(&eb->refs)) {
 		rcu_read_unlock();
@@ -6141,24 +6139,22 @@ struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
 	if (!eb)
 		return ERR_PTR(-ENOMEM);
 	eb->fs_info = fs_info;
-again:
-	ret = radix_tree_preload(GFP_NOFS);
-	if (ret) {
+
+	do {
+		ret = xa_insert(&fs_info->extent_buffers,
+				start >> fs_info->sectorsize_bits,
+				eb, GFP_NOFS);
+		if (ret == -ENOMEM) {
 			exists = ERR_PTR(ret);
 			goto free_eb;
 		}
-	spin_lock(&fs_info->buffer_lock);
-	ret = radix_tree_insert(&fs_info->buffer_radix,
-				start >> fs_info->sectorsize_bits, eb);
-	spin_unlock(&fs_info->buffer_lock);
-	radix_tree_preload_end();
-	if (ret == -EEXIST) {
+		if (ret == -EBUSY) {
 			exists = find_extent_buffer(fs_info, start);
 			if (exists)
 				goto free_eb;
-		else
-			goto again;
 		}
+	} while (ret);
+
 	check_buffer_tree_ref(eb);
 	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
 
@@ -6333,25 +6329,22 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 	}
 	if (uptodate)
 		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-again:
-	ret = radix_tree_preload(GFP_NOFS);
-	if (ret) {
+
+	do {
+		ret = xa_insert(&fs_info->extent_buffers,
+				start >> fs_info->sectorsize_bits,
+				eb, GFP_NOFS);
+		if (ret == -ENOMEM) {
 			exists = ERR_PTR(ret);
 			goto free_eb;
 		}
-
-	spin_lock(&fs_info->buffer_lock);
-	ret = radix_tree_insert(&fs_info->buffer_radix,
-				start >> fs_info->sectorsize_bits, eb);
-	spin_unlock(&fs_info->buffer_lock);
-	radix_tree_preload_end();
-	if (ret == -EEXIST) {
+		if (ret == -EBUSY) {
 			exists = find_extent_buffer(fs_info, start);
 			if (exists)
 				goto free_eb;
-		else
-			goto again;
 		}
+	} while (ret);
+
 	/* add one reference for the tree */
 	check_buffer_tree_ref(eb);
 	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
@@ -6396,10 +6389,8 @@ static int release_extent_buffer(struct extent_buffer *eb)
 
 			spin_unlock(&eb->refs_lock);
 
-			spin_lock(&fs_info->buffer_lock);
-			radix_tree_delete(&fs_info->buffer_radix,
+			xa_erase(&fs_info->extent_buffers,
 				 eb->start >> fs_info->sectorsize_bits);
-			spin_unlock(&fs_info->buffer_lock);
 		} else {
 			spin_unlock(&eb->refs_lock);
 		}
@@ -7344,42 +7335,25 @@ void memmove_extent_buffer(const struct extent_buffer *dst,
 	}
 }
 
-#define GANG_LOOKUP_SIZE	16
 static struct extent_buffer *get_next_extent_buffer(
 		struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
 {
-	struct extent_buffer *gang[GANG_LOOKUP_SIZE];
-	struct extent_buffer *found = NULL;
+	struct extent_buffer *eb;
+	unsigned long index;
 	u64 page_start = page_offset(page);
-	u64 cur = page_start;
 
 	ASSERT(in_range(bytenr, page_start, PAGE_SIZE));
 	lockdep_assert_held(&fs_info->buffer_lock);
 
-	while (cur < page_start + PAGE_SIZE) {
-		int ret;
-		int i;
-
-		ret = radix_tree_gang_lookup(&fs_info->buffer_radix,
-				(void **)gang, cur >> fs_info->sectorsize_bits,
-				min_t(unsigned int, GANG_LOOKUP_SIZE,
-				      PAGE_SIZE / fs_info->nodesize));
-		if (ret == 0)
-			goto out;
-		for (i = 0; i < ret; i++) {
+	xa_for_each_start(&fs_info->extent_buffers, index, eb,
+			  page_start >> fs_info->sectorsize_bits) {
+		if (in_range(eb->start, page_start, PAGE_SIZE))
+			return eb;
+		else if (eb->start >= page_start + PAGE_SIZE)
 		        /* Already beyond page end */
-			if (gang[i]->start >= page_start + PAGE_SIZE)
-				goto out;
-			/* Found one */
-			if (gang[i]->start >= bytenr) {
-				found = gang[i];
-				goto out;
-			}
-		}
-		cur = gang[ret - 1]->start + gang[ret - 1]->len;
+			return NULL;
 	}
-out:
-	return found;
+	return NULL;
 }
 
 static int try_release_subpage_extent_buffer(struct page *page)

fs/btrfs/tests/btrfs-tests.c

@@ -150,8 +150,8 @@ struct btrfs_fs_info *btrfs_alloc_dummy_fs_info(u32 nodesize, u32 sectorsize)
 
 void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info)
 {
-	struct radix_tree_iter iter;
-	void **slot;
+	unsigned long index;
+	struct extent_buffer *eb;
 	struct btrfs_device *dev, *tmp;
 
 	if (!fs_info)
@@ -163,25 +163,9 @@ void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info)
 
 	test_mnt->mnt_sb->s_fs_info = NULL;
 
-	spin_lock(&fs_info->buffer_lock);
-	radix_tree_for_each_slot(slot, &fs_info->buffer_radix, &iter, 0) {
-		struct extent_buffer *eb;
-
-		eb = radix_tree_deref_slot_protected(slot, &fs_info->buffer_lock);
-		if (!eb)
-			continue;
-		/* Shouldn't happen but that kind of thinking creates CVE's */
-		if (radix_tree_exception(eb)) {
-			if (radix_tree_deref_retry(eb))
-				slot = radix_tree_iter_retry(&iter);
-			continue;
-		}
-		slot = radix_tree_iter_resume(slot, &iter);
-		spin_unlock(&fs_info->buffer_lock);
+	xa_for_each(&fs_info->extent_buffers, index, eb) {
 		free_extent_buffer_stale(eb);
-		spin_lock(&fs_info->buffer_lock);
 	}
-	spin_unlock(&fs_info->buffer_lock);
 
 	btrfs_mapping_tree_free(&fs_info->mapping_tree);
 	list_for_each_entry_safe(dev, tmp, &fs_info->fs_devices->devices,