Revert "btrfs: turn fs_info member buffer_radix into XArray"

This reverts commit 8ee922689d67b7cfa6acbe2aa1ee76ac72e6fc8a.

Revert the xarray conversion, there's a problem with potential
sleep-inside-spinlock [1] when calling xa_insert that triggers GFP_NOFS
allocation. The radix tree used the preloading mechanism to avoid
sleeping but this is not available in xarray.

Conversion from spin lock to mutex is possible but at time of rc6 is
riskier than a clean revert.

[1] https://lore.kernel.org/linux-btrfs/cover.1657097693.git.fdmanana@suse.com/

Reported-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 74 insertions, 48 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 9c250b8cd548..31729b1be5f3 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2966,7 +2966,7 @@ static void begin_page_read(struct btrfs_fs_info *fs_info, struct page *page)
 }
 
 /*
- * Find extent buffer for a given bytenr.
+ * Find extent buffer for a givne bytenr.
  *
  * This is for end_bio_extent_readpage(), thus we can't do any unsafe locking
  * in endio context.
@@ -2985,9 +2985,11 @@ static struct extent_buffer *find_extent_buffer_readpage(
 		return (struct extent_buffer *)page->private;
 	}
 
-	/* For subpage case, we need to lookup extent buffer xarray */
-	eb = xa_load(&fs_info->extent_buffers,
-		     bytenr >> fs_info->sectorsize_bits);
+	/* For subpage case, we need to lookup buffer radix tree */
+	rcu_read_lock();
+	eb = radix_tree_lookup(&fs_info->buffer_radix,
+			       bytenr >> fs_info->sectorsize_bits);
+	rcu_read_unlock();
 	ASSERT(eb);
 	return eb;
 }
@@ -4434,8 +4436,8 @@ static struct extent_buffer *find_extent_buffer_nolock(
 	struct extent_buffer *eb;
 
 	rcu_read_lock();
-	eb = xa_load(&fs_info->extent_buffers,
-		     start >> fs_info->sectorsize_bits);
+	eb = radix_tree_lookup(&fs_info->buffer_radix,
+			       start >> fs_info->sectorsize_bits);
 	if (eb && atomic_inc_not_zero(&eb->refs)) {
 		rcu_read_unlock();
 		return eb;
@@ -6128,22 +6130,24 @@ struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
 	if (!eb)
 		return ERR_PTR(-ENOMEM);
 	eb->fs_info = fs_info;
-
-	do {
-		ret = xa_insert(&fs_info->extent_buffers,
-				start >> fs_info->sectorsize_bits,
-				eb, GFP_NOFS);
-		if (ret == -ENOMEM) {
-			exists = ERR_PTR(ret);
+again:
+	ret = radix_tree_preload(GFP_NOFS);
+	if (ret) {
+		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) {
+		exists = find_extent_buffer(fs_info, start);
+		if (exists)
 			goto free_eb;
-		}
-		if (ret == -EBUSY) {
-			exists = find_extent_buffer(fs_info, start);
-			if (exists)
-				goto free_eb;
-		}
-	} while (ret);
-
+		else
+			goto again;
+	}
 	check_buffer_tree_ref(eb);
 	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
 
@@ -6318,22 +6322,25 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 	}
 	if (uptodate)
 		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-
-	do {
-		ret = xa_insert(&fs_info->extent_buffers,
-				start >> fs_info->sectorsize_bits,
-				eb, GFP_NOFS);
-		if (ret == -ENOMEM) {
-			exists = ERR_PTR(ret);
+again:
+	ret = radix_tree_preload(GFP_NOFS);
+	if (ret) {
+		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) {
+		exists = find_extent_buffer(fs_info, start);
+		if (exists)
 			goto free_eb;
-		}
-		if (ret == -EBUSY) {
-			exists = find_extent_buffer(fs_info, start);
-			if (exists)
-				goto free_eb;
-		}
-	} while (ret);
-
+		else
+			goto again;
+	}
 	/* add one reference for the tree */
 	check_buffer_tree_ref(eb);
 	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
@@ -6378,8 +6385,10 @@ static int release_extent_buffer(struct extent_buffer *eb)
 
 			spin_unlock(&eb->refs_lock);
 
-			xa_erase(&fs_info->extent_buffers,
-				 eb->start >> fs_info->sectorsize_bits);
+			spin_lock(&fs_info->buffer_lock);
+			radix_tree_delete(&fs_info->buffer_radix,
+					  eb->start >> fs_info->sectorsize_bits);
+			spin_unlock(&fs_info->buffer_lock);
 		} else {
 			spin_unlock(&eb->refs_lock);
 		}
@@ -7324,25 +7333,42 @@ 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 *eb;
-	unsigned long index;
+	struct extent_buffer *gang[GANG_LOOKUP_SIZE];
+	struct extent_buffer *found = NULL;
 	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);
 
-	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 */
-			return NULL;
+	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++) {
+			/* 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;
 }
 
 static int try_release_subpage_extent_buffer(struct page *page)