On 7/14/22 05:23, Lukas Czerner wrote:
This does not seem right. we should never work with block number smaller
than s_first_data_block. The first 1024 bytes of the file system are
unused and in case we have 1k block size, the entire first block is
unused.
I guess the image we work here with is corrupted, from the log it seems
that it was noticed correctly so the question is why did we still ended
up calling ext4_free_blocks() ? Seems like this should have been stopped
earlier by ext4_clear_blocks() ?
I did notice that in ext4_mb_clear_bb() we call
ext4_get_group_no_and_offset() before ext4_inode_block_valid() but
again we should have caught this problem earlier.
Can you link me the file system image that generated this problem?
ok, I got the syzkaller C repro to work. The problem is that it's
bigalloc file system and the 'block' and 'count' to free in
ext4_free_blocks will get adjusted after the ext4_inode_block_valid().
We should make sure that if this happens we also clear the
EXT4_FREE_BLOCKS_VALIDATED. Additonally the ext4_inode_block_valid()
in ext4_mb_clear_bb() should be called*before* the values are taken for
granted. I'll prepare a patch to fix this.
Thank you for feedback Lukas. Please CC me on your patch so I could test it.
--
Thanks,
Tadeusz
