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

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Message-ID: <CAGETcx-F8G3dcN-VTMrbya_=19zXP=S2ORA_qZqy+yND7S41_Q@mail.gmail.com>
Date:   Wed, 6 Dec 2023 19:09:06 -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>
Subject: Re: [PATCH 0/2] Synchronize DT overlay removal with devlink removals

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.

-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
> >