linux-kernel - Re: [PATCH v3 0/2] Synchronize DT overlay removal with devlink removals

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Date: Mon, 4 Mar 2024 09:02:48 -0600
From: Rob Herring <robh@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>,
	Saravana Kannan <saravanak@...gle.com>
Cc: 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>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Nuno Sa <nuno.sa@...log.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 0/2] Synchronize DT overlay removal with devlink
 removals

On Thu, Feb 29, 2024 at 11:52:01AM +0100, Herve Codina wrote:
> Hi,

Please CC Saravana on this.

> 
> 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/20231130174126.688486-1-herve.codina@bootlin.com/
> this v3 series:
> - add the missing device.h
> 
> 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 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: overlay: Synchronize of_overlay_remove() with the devlink removals
> 
>  drivers/base/core.c    | 26 +++++++++++++++++++++++---
>  drivers/of/overlay.c   | 10 +++++++++-
>  include/linux/device.h |  1 +
>  3 files changed, 33 insertions(+), 4 deletions(-)
> 
> -- 
> 2.43.0
>