linux-kernel - Re: [PATCH v3] driver core: Fix SYNC_STATE

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Date:   Mon, 25 May 2020 13:31:27 +0200
From:   Michael Walle <michael@...le.cc>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     stable <stable@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] driver core: Fix SYNC_STATE_ONLY device link
 implementation

Am 2020-05-23 00:47, schrieb Michael Walle:
> Am 2020-05-23 00:21, schrieb Saravana Kannan:
>> On Fri, May 22, 2020 at 11:41 AM Michael Walle <michael@...le.cc> 
>> wrote:
>>> 
>>> Am Mon, 18 May 2020 23:30:00 -0700
>>> schrieb Saravana Kannan <saravanak@...gle.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.

btw. this only happens on linux-next (tested with next-20200522), not on
5.7-rc7 (which has the same two patches of yours)

-michael