Re: [PATCH v2] driver core: Update device link status correctly for SYNC_STATE_ONLY links

[Michael Walle]

Am 2020-05-26 23:45, schrieb Saravana Kannan:
> On Tue, May 26, 2020 at 2:13 PM Michael Walle <michael@xxxxxxxx> wrote:
> > Am 2020-05-26 21:43, schrieb Saravana Kannan:
> > > When SYNC_STATE_ONLY support was added in commit 05ef983e0d65 ("driver
> > > core: Add device link support for SYNC_STATE_ONLY flag"),
> > > SYNC_STATE_ONLY links were treated similar to STATELESS links in terms
> > > of not blocking consumer probe if the supplier hasn't probed yet.
> > >
> > > That caused a SYNC_STATE_ONLY device link's status to not get updated.
> > > Since SYNC_STATE_ONLY device link is no longer useful once the
> > > consumer probes, commit 21c27f06587d ("driver core: Fix
> > > SYNC_STATE_ONLY device link implementation") addresses the status
> > > update issue by deleting the SYNC_STATE_ONLY device link instead of
> > > complicating the status update code.
> > >
> > > However, there are still some cases where we need to update the status
> > > of a SYNC_STATE_ONLY device link. This is because a SYNC_STATE_ONLY
> > > device link can later get converted into a normal MANAGED device link
> > > when a normal MANAGED device link is created between a supplier and
> > > consumer that already have a SYNC_STATE_ONLY device link between them.
> > >
> > > If a SYNC_STATE_ONLY device link's status isn't maintained correctly
> > > till it's converted to a normal MANAGED device link, then the normal
> > > MANAGED device link will end up with a wrong link status. This can
> > > cause
> > > a warning stack trace[1] when the consumer device probes successfully.
> > >
> > > This commit fixes the SYNC_STATE_ONLY device link status update issue
> > > where it wouldn't transition correctly from DL_STATE_DORMANT or
> > > DL_STATE_AVAILABLE to DL_STATE_CONSUMER_PROBE. It also resets the
> > > status
> > > back to DL_STATE_DORMANT or DL_STATE_AVAILABLE if the consumer probe
> > > fails.
> > >
> > > [1] - https://lore.kernel.org/lkml/20200522204120.3b3c9ed6@apollo/
> > > Fixes: 05ef983e0d65 ("driver core: Add device link support for
> > > SYNC_STATE_ONLY flag")
> > > Fixes: 21c27f06587d ("driver core: Fix SYNC_STATE_ONLY device link
> > > implementation")
> > > Reported-by: Michael Walle <michael@xxxxxxxx>
> > > Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
> > > ---
> > >
> > > v1->v2:
> > > - Added code to "revert" the link status if consumer probe fails
> > >
> > > Greg,
> > >
> > > I think this is the issue Michael ran into. I'd like him to test the
> > > fix
> > > before it's pulled in.
> > >
> > > Michael,
> > >
> > > If you can test this on the branch you saw the issue in and give a
> > > Tested-by if it works, that'd be great.
> >
> > with v2 I'm triggering the
> >    WARN_ON(!(link->status & DL_FLAG_SYNC_STATE_ONLY));
> > in __device_links_no_driver().
>
> Thanks for the logs! The WARNING is due to a dump typo in this line. I
> should be checking link->flags, not link->status here. I'll send out a
> v3, but you can test with this change too.

Ahh, right. With that fix you can add:

Tested-by: Michael Walle <michael@xxxxxxxx>

Thanks,
-michael