New: Data Loss (flex_bg and ext4_mb_generate_buddy errors)
http://bugzilla.kernel.org/show_bug.cgi?id=15576
Summary: Data Loss (flex_bg and ext4_mb_generate_buddy errors)
Product: File System
Version: 2.5
Kernel Version: Linux elitemx-desktop 2.6.31-20-generic #58-Ubuntu SMP
Fri Mar 12 05:23:09 UTC 2010 i686 GNU/Linux
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: ext4
AssignedTo: [email protected]
ReportedBy: [email protected]
Regression: No
# create a 484 cylinder disk [3.7 GB] dd of=disk.bin bs=512 count=0 seek=$((484*255*63))
# associate with loop device losetup /dev/loop0 disk.bin
# generate bad blocks file [600 MB] for((i=360491;i<=497992;i++)); do echo $i; done > omit
# format disk with ext4 mkfs.ext4 -l omit /dev/loop0
# mount disk mkdir foobar; mount /dev/loop0 foobar
# create a 2 GB file cd foobar; dd if=/dev/zero bs=1024 count=$((1024 * 1024 * 2))
# check dmesg [ 9200.006021] EXT4-fs error (device loop0): ext4_mb_generate_buddy: EXT4-fs: group 12: 0 blocks in bitmap, 2 in gd [ 9200.010311] EXT4-fs error (device loop0): ext4_mb_generate_buddy: EXT4-fs: group 13: 0 blocks in bitmap, 2 in gd [ 9200.010359] EXT4-fs error (device loop0): ext4_mb_generate_buddy: EXT4-fs: group 14: 0 blocks in bitmap, 2 in gd [ 9200.010683] EXT4-fs error (device loop0): ext4_mb_generate_buddy: EXT4-fs: group 15: 9911 blocks in bitmap, 9913 in gd
Worse off, however, if rather than creating a 2 GB file, you use this partition as the target root partition for installation using the latest [32-bit] Ubuntu installer ... consistently at 57 percent of the install ext4 reports data loss.
[ 1129.344600] EXT4-fs error (device sda1): ext4_mb_generate_buddy: EXT4-fs: group 12: 0 blocks in bitmap, 2 in gd [ 1129.344626] Aborting journal on device sda1:8. [ 1129.380671] EXT4-fs error (device sda1): ext4_journal_start_sb: Detected aborted journal [ 1129.380697] EXT4-fs (sda1): Remounting filesystem read-only [ 1129.492154] EXT4-fs (sda1): Remounting filesystem read-only [ 1129.542049] EXT4-fs error (device sda1): ext4_mb_generate_buddy: EXT4-fs: group 13: 0 blocks in bitmap, 2 in gd [ 1129.554043] EXT4-fs error (device sda1): ext4_mb_generate_buddy: EXT4-fs: group 14: 0 blocks in bitmap, 2 in gd [ 1129.574283] EXT4-fs error (device sda1): ext4_mb_generate_buddy: EXT4-fs: group 15: 9911 blocks in bitmap, 9913 in gd [ 1129.574343] mpage_da_map_blocks block allocation failed for inode 41510 at logical offset 0 with max blocks 6 with error -30 [ 1129.574352] This should not happen.!! Data will be lost [ 1129.574393] ext4_da_writepages: jbd2_start: 1000 pages, ino 41510; err -30 [ 1129.574406] Pid: 11796, comm: pdflush Not tainted 2.6.31-14-generic #48-Ubuntu [ 1129.574414] Call Trace: [ 1129.574440] [<c056e41c>] ? printk+0x18/0x1c [ 1129.574456] [<c0266162>] ext4_da_writepages+0x452/0x490 [ 1129.574474] [<c01ba551>] do_writepages+0x21/0x40 [ 1129.574489] [<c02033fe>] writeback_single_inode+0x16e/0x3d0 [ 1129.574503] [<c0150510>] ? process_timeout+0x0/0x10 [ 1129.574515] [<c0203afd>] generic_sync_sb_inodes+0x38d/0x4a0 [ 1129.574528] [<c0203ced>] writeback_inodes+0x4d/0xe0 [ 1129.574539] [<c01b9432>] wb_kupdate+0xa2/0x110 [ 1129.574551] [<c01bac27>] __pdflush+0xf7/0x1f0 [ 1129.574562] [<c01bad20>] ? pdflush+0x0/0x40 [ 1129.574573] [<c01bad20>] ? pdflush+0x0/0x40 [ 1129.574583] [<c01bad59>] pdflush+0x39/0x40 [ 1129.574594] [<c01b9390>] ? wb_kupdate+0x0/0x110 [ 1129.574606] [<c015bf8c>] kthread+0x7c/0x90 [ 1129.574616] [<c015bf10>] ? kthread+0x0/0x90 [ 1129.574630] [<c0104007>] kernel_thread_helper+0x7/0x10
Signature · 3 lines
Configure bugmail: http://bugzilla.kernel.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are watching the assignee of the bug.
Quoted 11 lines · On Fri, Mar 19, 2010 at 01:05:23AM +0000, [email protected]…
# create a 484 cylinder disk [3.7 GB] dd of=disk.bin bs=512 count=0 seek=$((484*255*63))# associate with loop device losetup /dev/loop0 disk.bin# generate bad blocks file [600 MB] for((i=360491;i<=497992;i++)); do echo $i; done > omit# format disk with ext4 mkfs.ext4 -l omit /dev/loop0
This is an e2fsprogs bug. If you run e2fsck at this point, pass 5 errors will be reported, that exactly correspond with what you report the kernel ends up complaining about:
Free blocks count wrong for group #12 (2, counted=0).
Free blocks count wrong for group #13 (2, counted=0).
Free blocks count wrong for group #14 (2, counted=0).
Free blocks count wrong for group #15 (9913, counted=9911).
Free blocks count wrong (800730, counted=800722).
Quoted 4 lines
Worse off, however, if rather than creating a 2 GB file, you use this partition as the target root partition for installation using the latest [32-bit] Ubuntu installer ... consistently at 57 percent of the install ext4 reports data loss.
That's because the the file system is getting remounted read-only when the file system corruption is detected:
Quoted 3 lines
[ 1129.344600] EXT4-fs error (device sda1): ext4_mb_generate_buddy: EXT4-fs: group 12: 0 blocks in bitmap, 2 in gd [ 1129.380697] EXT4-fs (sda1): Remounting filesystem read-only
The basic idea behind this is when there is a discrepancy between the pass #5 summary statistics and the block allocation bitmap, the problem could be in the block allocation bitmap. (In this case it is the summary statistics, but there's no way for the code to know that.) If the block allocation bitmap is bogus, it's very dangerous to continue writing into the file system, since we may end up allocating blocks that are already in use by other files, and this would cause data loss when those data blocks get overwritten.
Once the file system is marked as read-only, data written just before the file system was remounted read-only can't be pushed out to disk, which is the reason for the warnign message:
Quoted 3 lines
[ 1129.574343] mpage_da_map_blocks block allocation failed for inode 41510 at logical offset 0 with max blocks 6 with error -30 [ 1129.574352] This should not happen.!! Data will be lost
(Error -30 is "EROFS".)
We should probably improve the error messages here, but there's not much else we can do.
The real core issue is the fact that mke2fs isn't doing the right thing when there are bad blocks and flex_bg is specified. It's something we don't test for, since in practice it never happens with modern disk drives.
- Ted