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From: Saravana Kannan <saravanak@google.com>
Date: Tue, 20 Feb 2024 16:19:21 -0800
Message-ID: <CAGETcx_Lv3EW+Mz94LJqzh1QW+NVmxrw6_HS3vYU6K5t8fci-A@mail.gmail.com>
Subject: Re: [PATCH 0/2] Synchronize DT overlay removal with devlink removals
To: Rob Herring <robh@kernel.org>
Cc: Herve Codina <herve.codina@bootlin.com>, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>, 
	Frank Rowand <frowand.list@gmail.com>, Lizhi Hou <lizhi.hou@amd.com>, Max Zhen <max.zhen@amd.com>, 
	Sonal Santan <sonal.santan@amd.com>, Stefano Stabellini <stefano.stabellini@xilinx.com>, 
	Jonathan Cameron <Jonathan.Cameron@huawei.com>, linux-kernel@vger.kernel.org, 
	devicetree@vger.kernel.org, Allan Nielsen <allan.nielsen@microchip.com>, 
	Horatiu Vultur <horatiu.vultur@microchip.com>, 
	Steen Hegelund <steen.hegelund@microchip.com>, 
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>, Nuno Sa <nuno.sa@analog.com>
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On Wed, Dec 6, 2023 at 7:09=E2=80=AFPM Saravana Kannan <saravanak@google.co=
m> wrote:
>
> On Wed, Dec 6, 2023 at 9:15=E2=80=AFAM Rob Herring <robh@kernel.org> wrot=
e:
> >
> > 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 mor=
e
> > > referenced (refcount =3D=3D 0), it is released and the reference to i=
ts
> > > 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 call=
s.
> > >
> > > In the sequence provided, the jobs are run too late, after the call t=
o
> > > __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() i=
n
> > > 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,
> > > Herv=C3=A9
> > >
> > > Herve Codina (2):
> > >   driver core: Introduce device_link_wait_removal()
> > >   of: overlay: Synchronize of_overlay_remove() with the devlink remov=
als
> > >
> > >  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
> > >