Re: BUG: unable to handle kernel paging request in z_erofs_decompress_queue

[Tudor Ambarus]

Hi, Gao,

On 15.12.2022 16:24, Gao Xiang wrote:
> Hi Tudor,
>
> On Thu, Dec 15, 2022 at 02:58:10PM +0200, Tudor Ambarus wrote:
> > Hi, Gao, Chao, Yue, Jeffle, all,
> >
> > Syzbot reported a bug at [1] that is reproducible in upstream kernel
> > since
> >    commit 47e4937a4a7c ("erofs: move erofs out of staging")
> >
> > and up to (inclusively)
> >    commit 2bfab9c0edac ("erofs: record the longest decompressed size in this
> > round")
> >
> > The first commit that makes this bug go away is:
> >    commit 267f2492c8f7 ("erofs: introduce multi-reference pclusters
> > (fully-referenced)")
> > Although, this commit looks like new support and not like an explicit
> > bug fix.
> >
> > I'd like to fix the lts kernels. I'm happy to try any suggestions or do
> > some tests. Please let me know if the bug rings a bell.
>
> Thanks for your report.  I will try to seek time to look at this this
> weekend.  But just from your description, I guess that there could be
> something wrong on several compressed extents pointing to the same
> blocks (i.e. the same pcluster).  But prior to commit 267f2492c8f7, such
> image is always considered as corrupted images.
>
> Anyway, I will look into that and see if there could be alternative ways
> to fix this rather than backport the whole multi-reference pcluster
> feature.  Yet I think no need to worry since such image is pretty
> crafted and should be used as normal images.

I guess to backport the multi-reference pcluster feature is not an
option for stable - just fixes are accepted. If you think it is worth
fixing the problem without adding new support, I can dive into it.
Let me know what you think.

Thanks,
ta

> Thanks,
> Gao Xiang
>
> > Thanks,
> > ta
> >
> > [1]
> > https://syzkaller.appspot.com/bug?id=a9b56d324d0de9233ad80633826fac76836d792a