linux-kernel - Re: [PATCH v2] driver core: Update device link status correctly for SYNC_STATE

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Message-ID: <CAGETcx_jyE2UyP4ovT3KXhjOenRhpUPQAqDtTcgfgenW5NGQgA@mail.gmail.com>
Date:   Tue, 26 May 2020 14:45:30 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Michael Walle <michael@...le.cc>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] driver core: Update device link status correctly for
 SYNC_STATE_ONLY links

On Tue, May 26, 2020 at 2:13 PM Michael Walle <michael@...le.cc> 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@...le.cc>
> > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > ---
> >
> > 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.

-Saravana