Re: [PATCH v3] driver core: Fix SYNC_STATE_ONLY device link implementation

From: Michael Walle <michael@walle.cc>
To: Saravana Kannan <saravanak@google.com>
Cc: stable <stable@vger.kernel.org>,
	Android Kernel Team <kernel-team@android.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] driver core: Fix SYNC_STATE_ONLY device link implementation
Date: Sat, 23 May 2020 00:47:39 +0200	[thread overview]
Message-ID: <41760105c011f9382f4d5fdc9feed017@walle.cc> (raw)
In-Reply-To: <CAGETcx85trw=rCM1+dmemMGKstFCq=Nn7HR2fyDyV0rTTQYtEQ@mail.gmail.com>

Am 2020-05-23 00:21, schrieb Saravana Kannan:
> On Fri, May 22, 2020 at 11:41 AM Michael Walle <michael@walle.cc> 
> wrote:
>> 
>> Am Mon, 18 May 2020 23:30:00 -0700
>> schrieb Saravana Kannan <saravanak@google.com>:
>> 
>> > When SYNC_STATE_ONLY support was added in commit 05ef983e0d65 ("driver
>> > core: Add device link support for SYNC_STATE_ONLY flag"),
>> > device_link_add() incorrectly skipped adding the new SYNC_STATE_ONLY
>> > device link to the supplier's and consumer's "device link" list.
>> >
>> > This causes multiple issues:
>> > - The device link is lost forever from driver core if the caller
>> >   didn't keep track of it (caller typically isn't expected to). This
>> > is a memory leak.
>> > - The device link is also never visible to any other code path after
>> >   device_link_add() returns.
>> >
>> > If we fix the "device link" list handling, that exposes a bunch of
>> > issues.
>> >
>> > 1. The device link "status" state management code rightfully doesn't
>> > handle the case where a DL_FLAG_MANAGED device link exists between a
>> > supplier and consumer, but the consumer manages to probe successfully
>> > before the supplier. The addition of DL_FLAG_SYNC_STATE_ONLY links
>> > break this assumption. This causes device_links_driver_bound() to
>> > throw a warning when this happens.
>> >
>> > Since DL_FLAG_SYNC_STATE_ONLY device links are mainly used for
>> > creating proxy device links for child device dependencies and aren't
>> > useful once the consumer device probes successfully, this patch just
>> > deletes DL_FLAG_SYNC_STATE_ONLY device links once its consumer device
>> > probes. This way, we avoid the warning, free up some memory and avoid
>> > complicating the device links "status" state management code.
>> >
>> > 2. Creating a DL_FLAG_STATELESS device link between two devices that
>> > already have a DL_FLAG_SYNC_STATE_ONLY device link will result in the
>> > DL_FLAG_STATELESS flag not getting set correctly. This patch also
>> > fixes this.
>> >
>> > Lastly, this patch also fixes minor whitespace issues.
>> 
>> My board triggers the
>>   WARN_ON(link->status != DL_STATE_CONSUMER_PROBE);
>> 
>> Full bootlog:
[..]

> Thanks for the log and report. I haven't spent too much time thinking
> about this, but can you give this a shot?
> https://lore.kernel.org/lkml/20200520043626.181820-1-saravanak@google.com/

I've already tried that, as this is already in linux-next. Doesn't fix 
it,
though.

-michael