linux-kernel - Re: [PATCH v5 0/2] Synchronize DT overlay removal with devlink removals

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Date: Wed, 20 Mar 2024 09:41:48 -0500
From: Rob Herring <robh@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Saravana Kannan <saravanak@...gle.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>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Nuno Sa <nuno.sa@...log.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v5 0/2] Synchronize DT overlay removal with devlink
 removals

On Fri, Mar 08, 2024 at 02:05:48PM -0600, Rob Herring wrote:
> On Thu, Mar 07, 2024 at 12:09:59PM +0100, Herve Codina wrote:
> > Hi,
> > 
> > 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).
> > 
> > Compared to the previous iteration:
> >   https://lore.kernel.org/linux-kernel/20240306085007.169771-1-herve.codina@bootlin.com/
> > this v5 series:
> > - Remove a 'Fixes' tag
> > - Update a comment
> > - Add 'Tested-by' and ''Reviewed-by' tags
> > 
> > This series handles cases reported by Luca [1] and Nuno [2].
> >   [1]: https://lore.kernel.org/all/20231220181627.341e8789@booty/
> >   [2]: https://lore.kernel.org/all/20240205-fix-device-links-overlays-v2-2-5344f8c79d57@analog.com/
> > 
> > Best regards,
> > Hervé
> > 
> > Changes v4 -> v5
> >   - Patch 1
> >     Remove the 'Fixes' tag
> >     Add 'Tested-by: Luca Ceresoli <luca.ceresoli@...tlin.com>'
> >     Add 'Reviewed-by: Nuno Sa <nuno.sa@...log.com>'
> > 
> >   - Patch 2
> >     Update comment as suggested
> >     Add 'Reviewed-by: Saravana Kannan <saravanak@...gle.com>'
> >     Add 'Tested-by: Luca Ceresoli <luca.ceresoli@...tlin.com>'
> >     Add 'Reviewed-by: Nuno Sa <nuno.sa@...log.com>'
> > 
> > Changes v3 -> v4
> >   - Patch 1
> >     Uses flush_workqueue() instead of drain_workqueue().
> > 
> >   - Patch 2
> >     Remove unlock/re-lock when calling device_link_wait_removal()
> >     Move device_link_wait_removal() call to of_changeset_destroy()
> >     Update commit log
> > 
> > Changes v2 -> v3
> >   - Patch 1
> >     No changes
> > 
> >   - Patch 2
> >     Add missing device.h
> > 
> > Changes v1 -> v2
> >   - Patch 1
> >     Rename the workqueue to 'device_link_wq'
> >     Add 'Fixes' tag and Cc stable
> > 
> >   - Patch 2
> >     Add device.h inclusion.
> >     Call device_link_wait_removal() later in the overlay removal
> >     sequence (i.e. in free_overlay_changeset() function).
> >     Drop of_mutex lock while calling device_link_wait_removal().
> >     Add	'Fixes'	tag and Cc stable
> > 
> > Herve Codina (2):
> >   driver core: Introduce device_link_wait_removal()
> >   of: dynamic: Synchronize of_changeset_destroy() with the devlink
> >     removals
> > 
> >  drivers/base/core.c    | 26 +++++++++++++++++++++++---
> >  drivers/of/dynamic.c   | 12 ++++++++++++
> >  include/linux/device.h |  1 +
> >  3 files changed, 36 insertions(+), 3 deletions(-)
> 
> This looks good to me. I can take this given the user is DT. Looking for 
> a R-by from Saravana and Ack from Greg. A R-by from Rafael would be 
> great too.

You may want to resend this as Greg may have seen the discussion and 
moved on.

Rob