Dave reported a NULL pointer deref.  This is caused because he thought he'd be
smart and add sanity checks to the extent_io bit operations, but he didn't
expect a tree to have a NULL mapping.  To fix this we just need to init the
relocation's processed_blocks with the btree_inode->i_mapping.  Thanks,

Reported-by: David Sterba <[email protected]>
Signed-off-by: Josef Bacik <[email protected]>
---
 fs/btrfs/relocation.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 6dbee86..1b50c41 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -4081,7 +4081,7 @@ out:
        return inode;
 }
 
-static struct reloc_control *alloc_reloc_control(void)
+static struct reloc_control *alloc_reloc_control(struct btrfs_fs_info *fs_info)
 {
        struct reloc_control *rc;
 
@@ -4092,7 +4092,8 @@ static struct reloc_control *alloc_reloc_control(void)
        INIT_LIST_HEAD(&rc->reloc_roots);
        backref_cache_init(&rc->backref_cache);
        mapping_tree_init(&rc->reloc_root_tree);
-       extent_io_tree_init(&rc->processed_blocks, NULL);
+       extent_io_tree_init(&rc->processed_blocks,
+                           fs_info->btree_inode->i_mapping);
        return rc;
 }
 
@@ -4109,7 +4110,7 @@ int btrfs_relocate_block_group(struct btrfs_root 
*extent_root, u64 group_start)
        int rw = 0;
        int err = 0;
 
-       rc = alloc_reloc_control();
+       rc = alloc_reloc_control(fs_info);
        if (!rc)
                return -ENOMEM;
 
@@ -4310,7 +4311,7 @@ int btrfs_recover_relocation(struct btrfs_root *root)
        if (list_empty(&reloc_roots))
                goto out;
 
-       rc = alloc_reloc_control();
+       rc = alloc_reloc_control(root->fs_info);
        if (!rc) {
                err = -ENOMEM;
                goto out;
-- 
1.7.7.6

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