On 31/05/2021 21:01, David Sterba wrote:

On Fri, May 21, 2021 at 06:11:04PM +0900, Johannes Thumshirn wrote:

quoted

--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c

@@ -1860,6 +1860,7 @@ noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
 				    u64 *end)
 {
 	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	u64 max_bytes = BTRFS_MAX_EXTENT_SIZE;
 	u64 delalloc_start;
 	u64 delalloc_end;

@@ -1868,6 +1869,9 @@ noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
 	int ret;
 	int loops = 0;
 
+	if (fs_info && fs_info->max_zone_append_size)

Do you really need to check for a valid fs_info? It's derived from an
inode so it must be valid or something is seriously wrong.

I thought it was because some selftest tripped over a NULL pointer, but it looks 
very much like cargo cult. I'll recheck.

quoted

+		max_bytes = ALIGN_DOWN(fs_info->max_zone_append_size,
+				       PAGE_SIZE);

Right now the page alignment sounds ok because the delalloc code works
on page granularity. There's the implicit assumpption that data blocks
are page-sized, but the whole delalloc engine works on pages so no
reason to use anything else.