Re: Patch 'writeback, cgroup: release dying cgwbs by switching attached inodes' leads to kernel crash

[Jan Kara <jack@suse.cz>]

On Wed 14-07-21 16:44:33, Boyang Xue wrote:
> Hi Roman,
> 
> On Wed, Jul 14, 2021 at 12:12 PM Roman Gushchin <guro@fb.com> wrote:
> >
> > On Wed, Jul 14, 2021 at 11:21:12AM +0800, Boyang Xue wrote:
> > > Hello,
> > >
> > > I'm not sure if this is the right place to report this bug, please
> > > correct me if I'm wrong.
> > >
> > > I found kernel-5.14.0-rc1 (built from the Linus tree) crash when it's
> > > running xfstests generic/256 on ext4 [1]. Looking at the call trace,
> > > it looks like the bug had been introduced by the commit
> > >
> > > c22d70a162d3 writeback, cgroup: release dying cgwbs by switching attached inodes
> > >
> > > It only happens on aarch64, not on x86_64, ppc64le and s390x. Testing
> > > was performed with the latest xfstests, and the bug can be reproduced
> > > on ext{2, 3, 4} with {1k, 2k, 4k} block sizes.
> >
> > Hello Boyang,
> >
> > thank you for the report!
> >
> > Do you know on which line the oops happens?
> 
> I was trying to inspect the vmcore with crash utility, but
> unfortunately it doesn't work.

Thanks for report!  Have you tried addr2line utility? Looking at the oops I
can see:

[ 4371.307867] pc : cleanup_offline_cgwbs_workfn+0x320/0x394

Which means there's probably heavy inlining going on (do you use LTO by
any chance?) because I don't think cleanup_offline_cgwbs_workfn() itself
would compile into ~1k of code (but I don't have much experience with
aarch64). Anyway, add2line should tell us.

Also pasting oops into scripts/decodecode on aarch64 machine should tell
us more about where and why the kernel crashed.

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR