Re: [PATCH 4.19 36/63] locking/lockdep: Add debug_locks check in __lock_downgrade()

[Sasha Levin]

On Sun, Sep 29, 2019 at 11:43:38PM +0900, Tetsuo Handa wrote:
> On 2019/09/29 22:54, Greg Kroah-Hartman wrote:
> > From: Waiman Long <longman@xxxxxxxxxx>
> >
> > [ Upstream commit 513e1073d52e55b8024b4f238a48de7587c64ccf ]
> >
> > Tetsuo Handa had reported he saw an incorrect "downgrading a read lock"
> > warning right after a previous lockdep warning. It is likely that the
> > previous warning turned off lock debugging causing the lockdep to have
> > inconsistency states leading to the lock downgrade warning.
> >
> > Fix that by add a check for debug_locks at the beginning of
> > __lock_downgrade().
>
> Please drop "[PATCH 4.19 36/63] locking/lockdep: Add debug_locks check in __lock_downgrade()".
> We had a revert patch shown below in the past.

We had a revert in the stable trees, but that revert was incorrect.

Take a look at commit 513e1073d52e55 upstream, it patches
__lock_set_class() (even though the subject line says
__lock_downgrade()). So this is not a backporting error as the revert
said it is, but is rather the intended location to be patched.

If this is actually wrong, then it should be addressed upstream first.

--
Thanks,
Sasha