EXT4: kernel BUG at fs/ext4/mballoc.c:1721!

While executing FS resize test against ext4 on a 4-way
POWER6 box with 2.6.31-rc8 kernel ran into following bug.

------------[ cut here ]------------
cpu 0x2: Vector: 700 (Program Check) at [c0000000f963ece0]
   pc: c000000000264d80: .ext4_mb_good_group+0x54/0x15c
   lr: c00000000026c9b0: .ext4_mb_regular_allocator+0x278/0x44c
   sp: c0000000f963ef60
  msr: 8000000000029032
 current = 0xc000000047b635a0
 paca    = 0xc000000000b62a00
   pid   = 32202, comm = dd
kernel BUG at fs/ext4/mballoc.c:1721!
enter ? for help
[link register   ] c00000000026c9b0 .ext4_mb_regular_allocator+0x278/0x44c
[c0000000f963ef60] c00000000026c99c .ext4_mb_regular_allocator+0x264/0x44c
(unreliable)
[c0000000f963f090] c00000000026cde0 .ext4_mb_new_blocks+0x25c/0x5b0
[c0000000f963f170] c000000000263260 .ext4_ext_get_blocks+0xd18/0xf2c
[c0000000f963f2f0] c0000000002404a8 .ext4_get_blocks+0x1b8/0x438
[c0000000f963f3c0] c000000000241d8c .ext4_get_block+0xe8/0x15c
[c0000000f963f480] c00000000018e1c0 .__block_prepare_write+0x210/0x4b0
[c0000000f963f5c0] c00000000018e698 .block_write_begin+0xa8/0x13c
[c0000000f963f680] c000000000243be4 .ext4_write_begin+0x198/0x324
[c0000000f963f790] c000000000112e50 .generic_file_buffered_write+0x140/0x37c
[c0000000f963f8d0] c00000000011364c
.__generic_file_aio_write_nolock+0x37c/0x3e0
[c0000000f963f9d0] c0000000001140e0 .generic_file_aio_write+0x88/0x120
[c0000000f963fa90] c000000000239250 .ext4_file_write+0xe4/0x1a4
[c0000000f963fb40] c00000000015e1f4 .do_sync_write+0xcc/0x130
[c0000000f963fce0] c00000000015ef44 .vfs_write+0xd0/0x1dc
[c0000000f963fd80] c00000000015f158 .SyS_write+0x58/0xa0
[c0000000f963fe30] c000000000008534 syscall_exit+0x0/0x40

--- Exception: c01 (System Call) at 00000fff8fd1a8f8

SP (fffc6270e00) is in userspace

During the first 3 runs i did not see this issue, so might
not be able to recreate this again. I have captured the dmesg
log and have attached it.

ext4 fs was created and mounted using :

mkfs.ext4 -b 1024 /dev/sda4 3943948
mount  -t ext4 -o errors=panic,data=journal /dev/sda4 /mnt/tmp/

The corresponding c code is :

1718         struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb,
group);
1719 1720         BUG_ON(cr < 0 || cr >= 4);
1721         BUG_ON(EXT4_MB_GRP_NEED_INIT(grp));
1722    ^^^^^^^^^^^^^^^^^^^^
1723         free = grp->bb_free;

Thanks
-Sachin


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Sachin Sant
IBM Linux Technology Center
India Systems and Technology Labs
Bangalore, India
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