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

[Michael Walle]

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@xxxxxxxx> 
> > wrote:
> > > Am Mon, 18 May 2020 23:30:00 -0700
> > > schrieb Saravana Kannan <saravanak@xxxxxxxxxx>:
> > >
> > > > 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@xxxxxxxxxx/
>
> 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