JBD2/ext4 error

JBD2/ext4 error

[Joseph Fannin]

Hi,

I'm hitting what's probably a bug in ext4 on one of my boxes. It
always happens on the boot partition, which is extentless, since it
seems likely GRUB will choke on extents.

On with the backtrace, already:

[ 4586.330338] JBD: grub-probe wants too many credits (266 > 256)
[ 4586.330384] ext4_da_writepages: jbd2_start: 18691 pages, ino 39; err -28
[ 4586.330398] Pid: 7365, comm: grub-probe Not tainted 2.6.27.4-1jhf-686 #4
[ 4586.330456]  [<d806a2f4>] ext4_da_writepages+0x165/0x2c0 [ext4]
[ 4586.330562]  [<d80babf2>] scsi_pool_alloc_command+0x30/0x4a [scsi_mod]
[ 4586.330647]  [<c01dd1fd>] blk_rq_map_sg+0xf1/0x240
[ 4586.330671]  [<c01e4558>] kobject_get+0xf/0x13
[ 4586.330690]  [<d806a18f>] ext4_da_writepages+0x0/0x2c0 [ext4]
[ 4586.330726]  [<c015edf2>] do_writepages+0x20/0x30
[ 4586.330745]  [<c0193f24>] __writeback_single_inode+0x15e/0x314
[ 4586.330767]  [<c02c70b6>] _spin_unlock_irq+0x24/0x2e
[ 4586.330779]  [<c01606c0>] mark_page_accessed+0x37/0x53
[ 4586.330793]  [<c0159b43>] read_cache_page_async+0xf9/0x101
[ 4586.330802]  [<c019ca5c>] blkdev_readpage+0x0/0xc
[ 4586.330823]  [<c0194485>] generic_sync_sb_inodes+0x229/0x32d
[ 4586.330835]  [<c0194607>] sync_inodes_sb+0x7e/0x86
[ 4586.330845]  [<c017cefe>] __fsync_super+0xa/0x61
[ 4586.330861]  [<c017cf5d>] fsync_super+0x8/0x14
[ 4586.330869]  [<c0198903>] fsync_bdev+0x14/0x2b
[ 4586.330879]  [<c01dd507>] blkdev_ioctl+0xac/0x70d
[ 4586.330888]  [<c01e4558>] kobject_get+0xf/0x13
[ 4586.330897]  [<c01de7ed>] exact_lock+0x7/0xd
[ 4586.330907]  [<c0245352>] kobj_lookup+0x112/0x140
[ 4586.330927]  [<c01ddb68>] exact_match+0x0/0x7
[ 4586.330936]  [<c02c727d>] unlock_kernel+0x3b/0x45
[ 4586.330944]  [<c019c7e6>] do_open+0x20c/0x288
[ 4586.330956]  [<c019c862>] blkdev_open+0x0/0x4d
[ 4586.330966]  [<c019c887>] blkdev_open+0x25/0x4d
[ 4586.330975]  [<c017a159>] __dentry_open+0x15a/0x226
[ 4586.330985]  [<c017a2a2>] nameidata_to_filp+0x1c/0x2c
[ 4586.330994]  [<c0183997>] do_filp_open+0x327/0x64c
[ 4586.331006]  [<c019beb4>] block_ioctl+0x13/0x16
[ 4586.331016]  [<c019bea1>] block_ioctl+0x0/0x16
[ 4586.331024]  [<c01850b7>] vfs_ioctl+0x1c/0x5f
[ 4586.331035]  [<c01854c1>] do_vfs_ioctl+0x3c7/0x3f9
[ 4586.331044]  [<c02c6edb>] _spin_lock+0x10/0x12
[ 4586.331067]  [<c0175c32>] virt_to_head_page+0x1f/0x2a
[ 4586.331086]  [<c0179f98>] do_sys_open+0xaa/0xb2
[ 4586.331094]  [<c0185534>] sys_ioctl+0x41/0x58
[ 4586.331103]  [<c01039af>] sysenter_do_call+0x12/0x2f

This kernel is simply 2.6.27.4 with the 2.6.27-ext4-2 patch applied,
though I've seen it also in a kernel built from the Debian 2.6.26
sources with some ext4 patch applied too -- I'm not sure which, I
don't have the patch or the source around anymore.

The backtrace varies a bit, but ext4_da_writepages is always on top.
It's not always grub-probe that sets it off -- often it happens while
generating a new initrd.  The error message will continue to repeat
until the fs is unmounted.  It can then be mounted without a problem
with ext3, though the files that were being modified when ext4 started
complaining will be corrupted.  Ext3 works fine; fsck thinks the fs is
fine.

The filesystem is mounted in writeback mode, and the journal size is
4100k, according to dumpe2fs.  Another box here has a similar boot
partition with a 4114k journal, and I don't think it's ever done
this.

Actually, I have two other boxes with the same setup.  Their disks are
ide, though -- a sata disk in one, and ide driven via the pata
drivers in the other.  The one I'm seeing a problem with is SCSI-only,
using that aic7000-series driver.

I don't know what's causing this.  Is there something I can do to
track this down?

--
Joseph Fannin
jfannin@gmail.com

Re: JBD2/ext4 error

[Theodore Tso]

On Sun, Nov 02, 2008 at 07:48:27PM -0500, Joseph Fannin wrote:
> Hi,
> 
> I'm hitting what's probably a bug in ext4 on one of my boxes. It
> always happens on the boot partition, which is extentless, since it
> seems likely GRUB will choke on extents.

Yeah, this looks like a 2.6.27 regression, introduced by commit a02908f1.

Mingming, can you check this:  I think in the function (in fs/ext4/inode.c):

static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
	if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
		return ext4_indirect_trans_blocks(inode, nrblocks, 0);
	return ext4_ext_index_trans_blocks(inode, nrblocks, 0);
}

... the last argument to ext4_indirect_trans_blocks and
ext4_ext_index_trans_blocks should be chunk, not 0.  

As result of this bug, we are massively overestimately the amount of
credits needed in the non-extent case, and with small journals, this
causes a failure.

We probably should do more testing with minimally sized journals to
make sure there aren't other problems which only show up with small
journals.

						- Ted

[PATCH] ext4: calculate journal credits correctly

[Theodore Ts'o]

This fixes a 2.6.27 regression which was introduced in commit a02908f1.

We weren't passing the chunk parameter down to the two subections,
ext4_indirect_trans_blocks() and ext4_ext_index_trans_blocks(), with
the result that massively overestimate the amount of credits needed by
ext4_da_writepages, especially in the non-extents case.  This causes
failures especially on /boot partitions, which tend to be small and
non-extent using since GRUB doesn't handle extents.

Thanks to Joseph Fannin for reporting this bug.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
 fs/ext4/inode.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 8dbf695..5a130b5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4580,9 +4580,10 @@ static int ext4_indirect_trans_blocks(struct inode *inode, int nrblocks,
 static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
 {
 	if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
-		return ext4_indirect_trans_blocks(inode, nrblocks, 0);
-	return ext4_ext_index_trans_blocks(inode, nrblocks, 0);
+		return ext4_indirect_trans_blocks(inode, nrblocks, chunk);
+	return ext4_ext_index_trans_blocks(inode, nrblocks, chunk);
 }
+
 /*
  * Account for index blocks, block groups bitmaps and block group
  * descriptor blocks if modify datablocks and index blocks
-- 
1.5.6.1.205.ge2c7.dirty

Re: [PATCH] ext4: calculate journal credits correctly

[Mingming Cao]

在 2008-11-06四的 14:51 -0500，Theodore Ts'o写道：
> This fixes a 2.6.27 regression which was introduced in commit a02908f1.
> 
> We weren't passing the chunk parameter down to the two subections,
> ext4_indirect_trans_blocks() and ext4_ext_index_trans_blocks(), with
> the result that massively overestimate the amount of credits needed by
> ext4_da_writepages, especially in the non-extents case.  This causes
> failures especially on /boot partitions, which tend to be small and
> non-extent using since GRUB doesn't handle extents.
> 
> Thanks to Joseph Fannin for reporting this bug.
> 
Thanks for fixing this up!

However, looking at the code path, I wasn't sure if we got the delalloc
credits right.  In ext4_da_writepages()->mpage_da_writepages(),  the
credits is calculated based on the assumption that mpage_da_writepages()
doing* one* single chunk of contigugous allocation? So only one single
extent credit is reserved (here you see the "chunk" flag passed from the
ext4_da_writepages)

__mpage_da_writepage() does do single chunk of block allocation at a
time, but mpage_da_writepages()->write_cache_pages() will loop the page
vectors and probably will calling writepage->__mpage_da_writepage->
mpage_da_map_blocks() multiple times?  Am I  missing anything?


> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> ---
>  fs/ext4/inode.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 8dbf695..5a130b5 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4580,9 +4580,10 @@ static int ext4_indirect_trans_blocks(struct inode *inode, int nrblocks,
>  static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
>  {
>  	if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
> -		return ext4_indirect_trans_blocks(inode, nrblocks, 0);
> -	return ext4_ext_index_trans_blocks(inode, nrblocks, 0);
> +		return ext4_indirect_trans_blocks(inode, nrblocks, chunk);
> +	return ext4_ext_index_trans_blocks(inode, nrblocks, chunk);
>  }
> +
>  /*
>   * Account for index blocks, block groups bitmaps and block group
>   * descriptor blocks if modify datablocks and index blocks

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Re: [PATCH] ext4: calculate journal credits correctly

[Aneesh Kumar K.V]

On Wed, Nov 12, 2008 at 04:03:42PM -0800, Mingming Cao wrote:
> 
> 在 2008-11-06四的 14:51 -0500，Theodore Ts'o写道：
> > This fixes a 2.6.27 regression which was introduced in commit a02908f1.
> > 
> > We weren't passing the chunk parameter down to the two subections,
> > ext4_indirect_trans_blocks() and ext4_ext_index_trans_blocks(), with
> > the result that massively overestimate the amount of credits needed by
> > ext4_da_writepages, especially in the non-extents case.  This causes
> > failures especially on /boot partitions, which tend to be small and
> > non-extent using since GRUB doesn't handle extents.
> > 
> > Thanks to Joseph Fannin for reporting this bug.
> > 
> Thanks for fixing this up!

This was sent to my gmail.com  id so missed it before.
> 
> However, looking at the code path, I wasn't sure if we got the delalloc
> credits right.  In ext4_da_writepages()->mpage_da_writepages(),  the
> credits is calculated based on the assumption that mpage_da_writepages()
> doing* one* single chunk of contigugous allocation? So only one single
> extent credit is reserved (here you see the "chunk" flag passed from the
> ext4_da_writepages)
> 
> __mpage_da_writepage() does do single chunk of block allocation at a
> time, but mpage_da_writepages()->write_cache_pages() will loop the page
> vectors and probably will calling writepage->__mpage_da_writepage->
> mpage_da_map_blocks() multiple times?  Am I  missing anything?
> 

mpage_da_writepages does block allocation for single chunk only.
ext4_da_writepages allocate credit needed for single chunk allocation.
write_cache_pages iterate through contiguous pages and build an in
memory extent. It then call get_blocks for 'x' blocks. After that
we map the blocks to the unmapped buffer_heads. Then we do
ext4_da_writepage which redirty pages which are not fully mapped. That
means we skip pages. We retry using mpage_data_writepages again.

-aneesh
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