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

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Message-ID: <0b68cbd8169d1c88a850b0fda3b1cf3f@walle.cc>
Date:   Tue, 26 May 2020 23:53:33 +0200
From:   Michael Walle <michael@...le.cc>
To:     Saravana Kannan <saravanak@...gle.com>
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

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>

Thanks,
-michael