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

[Sasha Levin]

On Mon, Sep 30, 2019 at 10:00:35AM -0400, Waiman Long wrote:
> On 9/29/19 9:46 PM, 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...
> >
> > 64aa348ed kernel/lockdep.c         (Peter Zijlstra            2008-08-11 09:30:21 +0200 4115) static int
> > 00ef9f734 kernel/lockdep.c         (Peter Zijlstra            2008-12-04 09:00:17 +0100 4116) __lock_set_class(struct lockdep_map *lock, const char *name,
> > 00ef9f734 kernel/lockdep.c         (Peter Zijlstra            2008-12-04 09:00:17 +0100 4117)            struct lock_class_key *key, unsigned int subclass,
> > 00ef9f734 kernel/lockdep.c         (Peter Zijlstra            2008-12-04 09:00:17 +0100 4118)            unsigned long ip)
> > 64aa348ed kernel/lockdep.c         (Peter Zijlstra            2008-08-11 09:30:21 +0200 4119) {
> > 64aa348ed kernel/lockdep.c         (Peter Zijlstra            2008-08-11 09:30:21 +0200 4120)   struct task_struct *curr = current;
> > 8c8889d8e kernel/locking/lockdep.c (Imre Deak                 2019-05-24 23:15:08 +0300 4121)   unsigned int depth, merged = 0;
> > 41c2c5b86 kernel/locking/lockdep.c (J. R. Okajima             2017-02-03 01:38:15 +0900 4122)   struct held_lock *hlock;
> > 64aa348ed kernel/lockdep.c         (Peter Zijlstra            2008-08-11 09:30:21 +0200 4123)   struct lock_class *class;
> > 64aa348ed kernel/lockdep.c         (Peter Zijlstra            2008-08-11 09:30:21 +0200 4124)   int i;
> > 64aa348ed kernel/lockdep.c         (Peter Zijlstra            2008-08-11 09:30:21 +0200 4125)
> > 513e1073d kernel/locking/lockdep.c (Waiman Long               2019-01-09 23:03:25 -0500 4126)   if (unlikely(!debug_locks))
> > 513e1073d kernel/locking/lockdep.c (Waiman Long               2019-01-09 23:03:25 -0500 4127)           return 0;
> > 513e1073d kernel/locking/lockdep.c (Waiman Long               2019-01-09 23:03:25 -0500 4128)
> >
> > 6419c4af7 kernel/locking/lockdep.c (J. R. Okajima             2017-02-03 01:38:17 +0900 4162) static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
> > 6419c4af7 kernel/locking/lockdep.c (J. R. Okajima             2017-02-03 01:38:17 +0900 4163) {
> > 6419c4af7 kernel/locking/lockdep.c (J. R. Okajima             2017-02-03 01:38:17 +0900 4164)   struct task_struct *curr = current;
> > 8c8889d8e kernel/locking/lockdep.c (Imre Deak                 2019-05-24 23:15:08 +0300 4165)   unsigned int depth, merged = 0;
> > 6419c4af7 kernel/locking/lockdep.c (J. R. Okajima             2017-02-03 01:38:17 +0900 4166)   struct held_lock *hlock;
> > 6419c4af7 kernel/locking/lockdep.c (J. R. Okajima             2017-02-03 01:38:17 +0900 4167)   int i;
> > 6419c4af7 kernel/locking/lockdep.c (J. R. Okajima             2017-02-03 01:38:17 +0900 4168)
> > 714925805 kernel/locking/lockdep.c (Waiman Long               2019-01-09 23:03:25 -0500 4169)   if (unlikely(!debug_locks))
> > 714925805 kernel/locking/lockdep.c (Waiman Long               2019-01-09 23:03:25 -0500 4170)           return 0;
> > 714925805 kernel/locking/lockdep.c (Waiman Long               2019-01-09 23:03:25 -0500 4171)
> >
> > commit 513e1073d52e55b8024b4f238a48de7587c64ccf
> > Author: Waiman Long <longman@xxxxxxxxxx>
> > Date:   Wed Jan 9 23:03:25 2019 -0500
> >
> >     locking/lockdep: Add debug_locks check in __lock_downgrade()
> >
> > commit 71492580571467fb7177aade19c18ce7486267f5
> > Author: Waiman Long <longman@xxxxxxxxxx>
> > Date:   Wed Jan 9 23:03:25 2019 -0500
> >
> >     locking/lockdep: Add debug_locks check in __lock_downgrade()
> As I had said before, it looks like the git-apply mixed up the location
> due to the fact that the hunks are exactly the same for both locations.
> So if the patch to be applied does not have the right line number, it
> will get applied to the wrong location first.

I very much agree, my point is that *both* patches are upstream right
now, and if one of those patches is wrong then it should be reverted
upstream, and we'd be happy to take the revert.

--
Thanks,
Sasha