Re: [PATCH] resize: check s_log_groups_per_flex before accessing flex groups

[Eric Sandeen <sandeen@redhat.com>]

Andreas Dilger wrote:
> On 2010-03-27, at 13:32, Eric Sandeen wrote:
>> #13549, Kernel oops while online resizing of an ext4 filesystem
>>
>> if groups_per_flex < 2, sbi->s_flex_groups[] doesn't get filled out,
>> and every other access to this first tests s_log_groups_per_flex;
>> same thing needs to happen in resize or we'll wander off into
>> a null pointer.
> 
> Does it even make sense to set INCOMPAT_FLEX_BG if we only have a single
> group per flexbg?  That is just a normal filesystem then.  That would be
> a separate bug in mke2fs.

yes, I really wondered about that, but we have this check throughout the
ext4 kernel code right now, so as a quick fix ...

(note in this case it was an ext3 fs converted to ext4, with tune2fs:)

# tune2fs -O extents,uninit_bg,dir_index,flex_bg,huge_file,dir_nlink,extra_isize fsfile

I haven't honestly looked at what it means to "turn on" flex_bg
for a filesystem not originally mkfs'd with it.  I'm not sure it does
anything other than setting the flag, leaving flex group size == group size.

Thanks,
-Eric