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

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Date:   Tue, 26 May 2020 15:00:37 -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 2:53 PM Michael Walle <michael@...le.cc> wrote:
>
> Am 2020-05-26 23:45, schrieb Saravana Kannan:
> > 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.
>
> Ahh, right. With that fix you can add:
>
> Tested-by: Michael Walle <michael@...le.cc>

Phew! Finally! Thanks.

-Saravana