Re: [PATCH] ext4: Fix bug on in ext4_es_cache_extent as ext4_split_extent_at failed

[Theodore Ts'o]

On Thu, Mar 25, 2021 at 10:29:25AM +0800, Ye Bin wrote:
> We got follow bug_on:
> [130747.323114] kernel BUG at fs/ext4/extents_status.c:762!
> [130747.323117] Internal error: Oops - BUG: 0 [#1] SMP
> ......
> [130747.334329] Call trace:
> [130747.334553]  ext4_es_cache_extent+0x150/0x168 [ext4]
> [130747.334975]  ext4_cache_extents+0x64/0xe8 [ext4]
> [130747.335368]  ext4_find_extent+0x300/0x330 [ext4]
> [130747.335759]  ext4_ext_map_blocks+0x74/0x1178 [ext4]
> [130747.336179]  ext4_map_blocks+0x2f4/0x5f0 [ext4]
> [130747.336567]  ext4_mpage_readpages+0x4a8/0x7a8 [ext4]
> [130747.336995]  ext4_readpage+0x54/0x100 [ext4]
> [130747.337359]  generic_file_buffered_read+0x410/0xae8
> [130747.337767]  generic_file_read_iter+0x114/0x190
> [130747.338152]  ext4_file_read_iter+0x5c/0x140 [ext4]
> [130747.338556]  __vfs_read+0x11c/0x188
> [130747.338851]  vfs_read+0x94/0x150
> [130747.339110]  ksys_read+0x74/0xf0
> 
> If call ext4_ext_insert_extent failed but new extent already inserted, we just
> update "ex->ee_len = orig_ex.ee_len", this will lead to extent overlap, then
> cause bug on when cache extent.

How did this happen in the first place?  It sounds like if the extent
was already inserted, that would be casue there was an on-disk file
system corruption, no?

In that case, shouldn't we call ext4_error() to declare the file
system has an inconsistency, so it can be fixed by fsck?

> If call ext4_ext_insert_extent failed don't update ex->ee_len with old value.
> Maybe there will lead to block leak, but it can be fixed by fsck later.

  	      	   	   	       - Ted