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

[Sasha Levin]

On Mon, Sep 30, 2019 at 10:46:39AM +0900, Tetsuo Handa wrote:
> On 2019/09/30 9:28, Sasha Levin wrote:
> > 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.
>
> Hmm, upstream has two commits with same author, same date, same subject, different hash, different content.
> I couldn't find from https://lkml.kernel.org/r/1547093005-26085-1-git-send-email-longman@xxxxxxxxxx that
> we want to patch both __lock_set_class() and __lock_downgrade(), but I found that the tip-bot has patched
> __lock_downgrade() on "2019-01-21 11:29" and __lock_set_class() on "2019-02-04  8:56".
> Seems that we by error patched both functions, though patching both functions should be harmless...

Right, there's a lot of confusion between the duplicate subject lines
and what this patch actually does. My point was that this is an upstream
issue rather than a stable issue, we're just aligning with upstream
here.

--
Thanks,
Sasha