Re: [PATCH v2] ext4: fix off by one issue in alloc_flex_gd()

[Baokun Li]

On 2024/9/27 22:14, Eric Sandeen wrote:
> On 9/27/24 8:33 AM, libaokun@xxxxxxxxxxxxxxx wrote:
> > From: Baokun Li <libaokun1@xxxxxxxxxx>
> ...
>
> > Delete the problematic plus 1 to fix the issue, and add a WARN_ON_ONCE()
> > to prevent the issue from happening again.
> >
> > Reported-by: Wesley Hershberger <wesley.hershberger@xxxxxxxxxxxxx>
> > Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2081231
> > Reported-by: Stéphane Graber <stgraber@xxxxxxxxxxxx>
> > Closes: https://lore.kernel.org/all/20240925143325.518508-1-aleksandr.mikhalitsyn@xxxxxxxxxxxxx/
> > Tested-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> > Tested-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> The patch has changed a little since I tested, but it still passes my testcase
> (as expected, no WARN ON etc) so looks good from that POV, thanks!
> -Eric

Hi Eric,

Thanks for testing it again!

The core modification logic remains unchanged from before.
Just added a max_resize_bg variable for exception fixing.

It is necessary to ensure that flex_gd->resize_bg does not exceed the
smaller of flexbg_size and MAX_RESIZE_BG before it is used. So we need
to record max_resize_bg, warn on resize_bg adjustment logic exceptions,
and use max_resize_bg to avoid subsequent resize complaints.


--
With Best Regards,
Baokun Li