Re: [syzbot] Re: [syzbot] [btrfs?] kernel BUG in __extent_writepage_io (2)

[syzbot <syzbot+ba3c0273042a898c230e@syzkaller.appspotmail.com>]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Re: [syzbot] [btrfs?] kernel BUG in __extent_writepage_io (2)
Author: lizhi.xu@windriver.com

#syz test

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 744e8952abb0..c81b23d0d73e 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -262,6 +262,7 @@ static void try_merge_map(struct btrfs_inode *inode, struct extent_map *em)
 			em->len += merge->len;
 			em->block_len += merge->block_len;
 			em->block_start = merge->block_start;
+			printk("em: %p, blockstart: %llu, mblockstart: %llu, %s\n", em, em->block_start, merge->block_start, __func__);
 			em->generation = max(em->generation, merge->generation);
 			em->flags |= EXTENT_FLAG_MERGED;
 
@@ -393,7 +394,11 @@ static int add_extent_mapping(struct btrfs_inode *inode,
 	if (ret)
 		return ret;
 
+	printk("em: %p, blockstart: %llu, em refs: %d, %s\n", 
+		em, em->block_start, refcount_read(&em->refs), __func__);
 	setup_extent_mapping(inode, em, modified);
+	printk("setuped, em: %p, blockstart: %llu, em refs: %d, %s\n", 
+		em, em->block_start, refcount_read(&em->refs), __func__);
 
 	if (!btrfs_is_testing(fs_info) && is_fstree(btrfs_root_id(root)))
 		percpu_counter_inc(&fs_info->evictable_extent_maps);
@@ -643,6 +648,8 @@ int btrfs_add_extent_mapping(struct btrfs_inode *inode,
 			}
 			free_extent_map(existing);
 		}
+	} else if (!ret) {
+		ASSERT(em->block_start != EXTENT_MAP_HOLE);
 	}
 
 	ASSERT(ret == 0 || ret == -EEXIST);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3a2b902b2d1f..b588381458df 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6972,7 +6972,9 @@ struct extent_map *btrfs_get_extent(struct btrfs_inode *inode,
 	}
 
 	write_lock(&em_tree->lock);
+	printk("em: %p, blockstart: %llu, start: %llu, len: %llu, %s\n", em, em->block_start, start, len, __func__);
 	ret = btrfs_add_extent_mapping(inode, &em, start, len);
+	printk("ret: %d, em: %p, blockstart: %llu, start: %llu, len: %llu, %s\n", ret, em, em->block_start, start, len, __func__);
 	write_unlock(&em_tree->lock);
 out:
 	btrfs_free_path(path);