linux-kernel - Re: [PATCH 0/2] Synchronize DT overlay removal with devlink removals

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Date: Tue, 20 Feb 2024 16:19:21 -0800
From: Saravana Kannan <saravanak@...gle.com>
To: Rob Herring <robh@...nel.org>
Cc: Herve Codina <herve.codina@...tlin.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Frank Rowand <frowand.list@...il.com>, Lizhi Hou <lizhi.hou@....com>, Max Zhen <max.zhen@....com>, 
	Sonal Santan <sonal.santan@....com>, Stefano Stabellini <stefano.stabellini@...inx.com>, 
	Jonathan Cameron <Jonathan.Cameron@...wei.com>, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, Allan Nielsen <allan.nielsen@...rochip.com>, 
	Horatiu Vultur <horatiu.vultur@...rochip.com>, 
	Steen Hegelund <steen.hegelund@...rochip.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>, Nuno Sa <nuno.sa@...log.com>
Subject: Re: [PATCH 0/2] Synchronize DT overlay removal with devlink removals

On Wed, Dec 6, 2023 at 7:09 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> On Wed, Dec 6, 2023 at 9:15 AM Rob Herring <robh@...nel.org> wrote:
> >
> > On Thu, Nov 30, 2023 at 06:41:07PM +0100, Herve Codina wrote:
> > > Hi,
> >
> > +Saravana for comment
>
> I'll respond to this within a week -- very swamped at the moment. The
> main thing I want to make sure is that we don't cause an indirect
> deadlock with this wait(). I'll go back and look at why we added the
> work queue and then check for device/devlink locking issues.
>

Sorry about the long delay, but I finally got back to this because
Nuno nudged me to review a similar patch they sent. I'll leave some
easy to address comments in the patches.

-Saravana

> -Saravana
>
> >
> > Looks okay to me though.
> >
> > >
> > > In the following sequence:
> > >   of_platform_depopulate(); /* Remove devices from a DT overlay node */
> > >   of_overlay_remove(); /* Remove the DT overlay node itself */
> > >
> > > Some warnings are raised by __of_changeset_entry_destroy() which  was
> > > called from of_overlay_remove():
> > >   ERROR: memory leak, expected refcount 1 instead of 2 ...
> > >
> > > The issue is that, during the device devlink removals triggered from the
> > > of_platform_depopulate(), jobs are put in a workqueue.
> > > These jobs drop the reference to the devices. When a device is no more
> > > referenced (refcount == 0), it is released and the reference to its
> > > of_node is dropped by a call to of_node_put().
> > > These operations are fully correct except that, because of the
> > > workqueue, they are done asynchronously with respect to function calls.
> > >
> > > In the sequence provided, the jobs are run too late, after the call to
> > > __of_changeset_entry_destroy() and so a missing of_node_put() call is
> > > detected by __of_changeset_entry_destroy().
> > >
> > > This series fixes this issue introducing device_link_wait_removal() in
> > > order to wait for the end of jobs execution (patch 1) and using this
> > > function to synchronize the overlay removal with the end of jobs
> > > execution (patch 2).
> > >
> > > Best regards,
> > > Hervé
> > >
> > > Herve Codina (2):
> > >   driver core: Introduce device_link_wait_removal()
> > >   of: overlay: Synchronize of_overlay_remove() with the devlink removals
> > >
> > >  drivers/base/core.c    | 26 +++++++++++++++++++++++---
> > >  drivers/of/overlay.c   |  6 ++++++
> > >  include/linux/device.h |  1 +
> > >  3 files changed, 30 insertions(+), 3 deletions(-)
> > >
> > > --
> > > 2.42.0
> > >