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References: <20240306085007.169771-1-herve.codina@bootlin.com> <20240306085007.169771-3-herve.codina@bootlin.com>
In-Reply-To: <20240306085007.169771-3-herve.codina@bootlin.com>
From: Saravana Kannan <saravanak@google.com>
Date: Wed, 6 Mar 2024 13:35:31 -0800
Message-ID: <CAGETcx9RFS7Z61FeCYXMxRSDXnMYhg_y96dgtbHp-3t_9x8+SA@mail.gmail.com>
Subject: Re: [PATCH v4 2/2] of: dynamic: Synchronize of_changeset_destroy()
 with the devlink removals
To: Herve Codina <herve.codina@bootlin.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>, 
	Rob Herring <robh+dt@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>, Luca Ceresoli <luca.ceresoli@bootlin.com>, 
	Nuno Sa <nuno.sa@analog.com>, Thomas Petazzoni <thomas.petazzoni@bootlin.com>, 
	stable@vger.kernel.org
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On Wed, Mar 6, 2024 at 12:51=E2=80=AFAM Herve Codina <herve.codina@bootlin.=
com> wrote:
>
> In the following sequence:
>   1) of_platform_depopulate()
>   2) of_overlay_remove()
>
> During the step 1, devices are destroyed and devlinks are removed.
> During the step 2, OF nodes are destroyed but
> __of_changeset_entry_destroy() can raise warnings related to missing
> of_node_put():
>   ERROR: memory leak, expected refcount 1 instead of 2 ...
>
> Indeed, during the devlink removals performed at step 1, the removal
> itself releasing the device (and the attached of_node) is done by a job
> queued in a workqueue and so, it is done asynchronously with respect to
> function calls.
> When the warning is present, of_node_put() will be called but wrongly
> too late from the workqueue job.
>
> In order to be sure that any ongoing devlink removals are done before
> the of_node destruction, synchronize the of_changeset_destroy() with the
> devlink removals.
>
> Fixes: 80dd33cf72d1 ("drivers: base: Fix device link removal")
> Cc: stable@vger.kernel.org
> Signed-off-by: Herve Codina <herve.codina@bootlin.com>
> ---
>  drivers/of/dynamic.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
> index 3bf27052832f..169e2a9ae22f 100644
> --- a/drivers/of/dynamic.c
> +++ b/drivers/of/dynamic.c
> @@ -9,6 +9,7 @@
>
>  #define pr_fmt(fmt)    "OF: " fmt
>
> +#include <linux/device.h>
>  #include <linux/of.h>
>  #include <linux/spinlock.h>
>  #include <linux/slab.h>
> @@ -667,6 +668,12 @@ void of_changeset_destroy(struct of_changeset *ocs)
>  {
>         struct of_changeset_entry *ce, *cen;
>
> +       /*
> +        * Wait for any ongoing device link removals before destroying so=
me of
> +        * nodes.
> +        */

Not going to ask you to revise this patch just for this, but this
comment isn't very useful. It's telling what you are doing. Not why.
And the function name is already clear on what you are doing.

Maybe something like this would be better at describing the "why"?
Free free to reword it.

When a device is deleted, the device links to/from it are also queued
for deletion. Until these device links are freed, the devices
themselves aren't freed. If the device being deleted is due to an
overlay change, this device might be holding a reference to a device
node that will be freed. So, wait until all already pending device
links are deleted before freeing a device node. This ensures we don't
free any device node that has a non-zero reference count.

Reviewed-by: Saravana Kannan <saravanak@google.com>

-Saravana

> +       device_link_wait_removal();
> +
>         list_for_each_entry_safe_reverse(ce, cen, &ocs->entries, node)
>                 __of_changeset_entry_destroy(ce);
>  }
> --
> 2.43.0
>