linux-kernel - btrfs resize ate my root node

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Date:	Mon, 7 Mar 2011 14:08:09 +0100
From:	Peter Stuge <peter@...ge.se>
To:	linux-kernel@...r.kernel.org
Subject: btrfs resize ate my root node

Hi,

I ran btrfsctl resize -r -3gb /dev/sda2 using wireless-testing.git
based on 2.6.38-rc6 and all seemed good. df reported reduced size so
I repartitioned and rebooted. Filesystem can no longer be mounted:

[10560.129038] device fsid b2408c2e83f55cc2-5f7a14e35f176484 devid 1 transid 341132 /dev/sdb2
[10560.133407] btrfs bad tree block start 0 34520006656
[10560.134031] btrfs bad tree block start 0 34520006656
[10560.134904] btrfs bad tree block start 0 34520006656
[10560.134912] btrfs: failed to read tree root on sdb2
[10560.137206] btrfs: open_ctree failed

btrfs-debug-tree and friends are similarly upset:

$ ./btrfs-debug-tree /dev/sdb2
btrfs-debug-tree: disk-io.c:739: open_ctree_fd: Assertion `!(!tree_root->node)' failed.

$ gdb --args ./btrfs-debug-tree /dev/sdb2
GNU gdb 6.8
..
(gdb) b disk-io.c:44
Breakpoint 1 at 0x8050db7: file disk-io.c, line 44.
..
Breakpoint 1, check_tree_block (root=0x946e2e8, buf=0x9471538) at disk-io.c:44
44              if (buf->start != btrfs_header_bytenr(buf))
(gdb) p buf->start
$1 = 20971520
..
Breakpoint 1, check_tree_block (root=0x946e2e8, buf=0x9472588) at disk-io.c:44
44              if (buf->start != btrfs_header_bytenr(buf))
(gdb) p buf->start
$2 = 20987904
..
Breakpoint 1, check_tree_block (root=0x946e2e8, buf=0x94735d8) at disk-io.c:44
44              if (buf->start != btrfs_header_bytenr(buf))
(gdb) p buf->start
$3 = 20983808

The above checks succeed but next time check_tree_block() is called
the check does not succeed.

Breakpoint 1, check_tree_block (root=0x946e008, buf=0x9474628) at disk-io.c:44
44              if (buf->start != btrfs_header_bytenr(buf))
(gdb) p buf->start
$4 = 34520006656
(gdb) p btrfs_header_bytenr(buf)
$5 = 0
..
(gdb) bt
#0  check_tree_block (root=0x946e008, buf=0x9474628) at disk-io.c:45
#1  0x080514fc in read_tree_block (root=0x946e008, bytenr=34520006656, 
    blocksize=4096, parent_transid=341132) at disk-io.c:207
#2  0x080531a7 in open_ctree_fd (fp=7, path=0xbfef322a "/dev/sdb2", 
    sb_bytenr=65536, writes=0) at disk-io.c:736
#3  0x08052a58 in open_ctree (filename=0xbfef322a "/dev/sdb2", sb_bytenr=0, 
    writes=0) at disk-io.c:587
#4  0x080735cf in main (ac=1, av=0xbfef2374) at debug-tree.c:148

This is disk-io.c:

732     blocksize = btrfs_level_size(tree_root,
                                     btrfs_super_root_level(disk_super));  
        generation = btrfs_super_generation(disk_super);  

        tree_root->node = read_tree_block(tree_root,
                                          btrfs_super_root(disk_super),
                                          blocksize, generation);
..
188     eb = btrfs_find_create_tree_block(root, bytenr, blocksize);
..
198             ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
                                      eb->start, &length, &multi, mirror_num);
..
206             ret = read_extent_from_disk(eb);
                if (ret == 0 && check_tree_block(root, eb) == 0 &&

This is the call that fails.


Where do I look next?


//Peter
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