Re: BISECT result: 6.0.0-RC kernels trigger Firefox snap bug with 6.0.0-rc3 through 6.0.0-rc7

[Phillip Lougher]

On 18/10/2022 13:59, Bagas Sanjaya wrote:
> On Tue, Oct 18, 2022 at 04:24:46PM +0800, Hsin-Yi Wang wrote:
> > Hi Jintao,
> >
> > Thanks for pointing out and sorry for missing this. Does the following
> > diff improve the issue?
> >
> > diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
> > index e56510964b229..7759bd70dfbf2 100644
> > --- a/fs/squashfs/file.c
> > +++ b/fs/squashfs/file.c
> > @@ -600,7 +600,7 @@ static void squashfs_readahead(struct
> > readahead_control *ractl)
> >
> >                          /* Last page (if present) may have trailing
> > bytes not filled */
> >                          bytes = res % PAGE_SIZE;
> > -                       if (pages[nr_pages - 1]->index == file_end && bytes)
> > +                       if ((pages[nr_pages - 1]->index >> shift) ==
> > file_end && bytes)
> >                                  memzero_page(pages[nr_pages - 1], bytes,
> >                                               PAGE_SIZE - bytes);
> >
> >
> > readahead only handles the case that the first page and the last page
> > have the same block index:
> >      index = pages[0]->index >> shift;
> >      if ((pages[nr_pages - 1]->index >> shift) != index)
> >          goto skip_pages;
> >
> > The diff above makes a difference to SQUASHFS_INVALID_BLK case, which
> > will not be handled by squashfs_readahead_fragment() if
> > index==file_end.
> > With the above diff, it will now be memzero_page().
>
> Hi Hsin-Yi Wang, thanks for the proposed diff. However, it was wrapped,
> so I have to manually type the changes.
>
> I compiled 6.1-rc1 with your diff applied. For testing, I have both
> hello-world and lxd snaps installed. No problems on running the former.
> On the latter, I got coredump when trying to start lxd services with
> `snap start lxd`. The coredump for lxd processes are attached.
>
>  From above, I think b09a7a036d2035 ("squashfs: support reading fragments in readahead call") should be reverted until we come up with proper solution.
>
> Thanks.

I am currently working with the snap developers to identify the issue.

When there is progress, I will post.

Phillip