On 2010-11-12, at 16:26, Bernd Schubert wrote:
> The real issue we want to debug with the patch below actually came up while
> stress testing Lustre using the RHEL5.5 kernel (so 2.6.32'ish ext4), but a
> more verbose error function should not hurt for vanilla ext4 either.
>
> make ext4_valid_block_bitmap() more verbose
>
> While running our stress test suite, ext4_valid_block_bitmap()
> frequently complains about an invalid block bitmap.
> However, e2fsck does not find anything. So in oder to be able
> to better debug this issue, make the function more verbose and
> let it complain about the two possible invalid bitmaps.
Bernd,
thanks for sending this in. I like the idea of making these messages more verbose, since they should rarely be hit and when they are it would be good to know why these checks failed.
> +/**
> + * ext4_get_group_desc() -- load group descriptor from disk
> + * @sb: super block
> + * @ext4_group_desc: blocks group descriptor
> + * @block_group block group to check
> + * @bh: pointer to the buffer head to store the block
> + * group descriptor
> + *
> + * return 0 on error or 1 if valid
> + */
> static int ext4_valid_block_bitmap(struct super_block *sb,
> struct ext4_group_desc *desc,
> unsigned int block_group,
The function name in the comment block does not actually match the function...
> @@ -254,16 +265,20 @@ static int ext4_valid_block_bitmap(struc
> + if (!ext4_test_bit(offset, bh->b_data)) {
> + ext4_warning(sb, "bad block bitmap block = %llu, offset = %d",
> + bitmap_blk, (int) offset);
> + valid = 0;
> + }
>
> /* check whether the inode bitmap block number is set */
> bitmap_blk = ext4_inode_bitmap(sb, desc);
> offset = bitmap_blk - group_first_block;
> + if (!ext4_test_bit(offset, bh->b_data)) {
> + ext4_warning(sb, "bad inode bitmap block = %llu, offset = %d",
> + bitmap_blk, (int) offset);
> + valid = 0;
This message (while correct) is a bit confusing, since it implies there is something wrong with the inode bitmap block itself, rather than the the bit in the block bitmap. I think it would be clearer to rewrite this as follows:
"unset bit for inode bitmap: block %llu, bit %u"
for consistency we should then change the block bitmap error to match.
While we are changing this code, all of the ext4_test_bit() checks should be wrapped in unlikely(), since we should very rarely be seeing these errors.
> @@ -271,14 +286,17 @@ static int ext4_valid_block_bitmap(struc
> + if (next_zero_bit < offset + EXT4_SB(sb)->s_itb_per_group) {
> + ext4_warning(sb, "bad inode table block = %llu, offset = %d",
> + bitmap_blk, (int) offset);
> + valid = 0;
Similarly, this implies that there is a bad inode table block, so I prefer:
"unset bit for inode table block %u: block %llu, bit %u"
where the "inode table block" value is, I think, (next_zero_bit - offset)
> + if (!valid)
> + ext4_error(sb, "Invalid block bitmap - block_group = %d",
> + block_group);
It would probably be worthwhile to also print the block number of the bitmap itself.
Cheers, Andreas
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