[PATCH v4 0/2] Synchronize DT overlay removal with devlink removals

From: Herve Codina <herve.codina@bootlin.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Saravana Kannan <saravanak@google.com>
Cc: 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>,
	Luca Ceresoli <luca.ceresoli@bootlin.com>,
	Nuno Sa <nuno.sa@analog.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Herve Codina <herve.codina@bootlin.com>
Subject: [PATCH v4 0/2] Synchronize DT overlay removal with devlink removals
Date: Wed,  6 Mar 2024 09:50:01 +0100	[thread overview]
Message-ID: <20240306085007.169771-1-herve.codina@bootlin.com> (raw)

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/20240229105204.720717-1-herve.codina@bootlin.com/
this v4 series:
- Uses flush_workqueue()
- Keep the of_mutex lock taken calling device_link_wait_removal()
- Perform the wait in of_changeset_destroy()

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 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   |  7 +++++++
 include/linux/device.h |  1 +
 3 files changed, 31 insertions(+), 3 deletions(-)

-- 
2.43.0