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References: <20240529073246.537459-1-alexander.stein@ew.tq-group.com>
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From: Rob Herring <robh@kernel.org>
Date: Wed, 29 May 2024 15:16:53 -0500
Message-ID: <CAL_Jsq+QMnjadq6+eH11BxvxTy4vQmqScwOs6sgL3T2gY-mMsg@mail.gmail.com>
Subject: Re: [PATCH 1/1] of: property: Fix device_node cleanup
To: Alexander Stein <alexander.stein@ew.tq-group.com>
Cc: Saravana Kannan <saravanak@google.com>, Shresth Prasad <shresthprasad7@gmail.com>, 
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
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On Wed, May 29, 2024 at 2:33=E2=80=AFAM Alexander Stein
<alexander.stein@ew.tq-group.com> wrote:
>
> '__free(device_node)' attached to remote will cause a double release:
> > OF: ERROR: of_node_release() detected bad of_node_put() on
> > /soc@0/bus@32c00000/dsi@32e60000
>
> In case remote is to be returned it must not be cleaned up by a call
> to of_node_put. The caller has to do that as the documentation mentions.
> Partly revert commit b94d24c08ee1a ("of: property: Remove calls to
> of_node_put") to fix it.
>
> Fixes: b94d24c08ee1 ("of: property: Remove calls to of_node_put")

I've dropped it now.

> Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> ---
> I get the following trace starting with next-20240529:
>
> OF: ERROR: of_node_release() detected bad of_node_put() on /soc@0/bus@32c=
00000/dsi@32e60000
> CPU: 0 PID: 11 Comm: kworker/u16:0 Not tainted 6.10.0-rc1-next-20240529+ =
#2511 610eecbb638fc5fab9a27e01b78203e8a379a280
> Hardware name: TQ-Systems i.MX8MPlus TQMa8MPxL on MBa8MPxL (DT)
> Workqueue: events_unbound deferred_probe_work_func
> Call trace:
>  dump_backtrace+0x90/0x10c
>  show_stack+0x14/0x1c
>  dump_stack_lvl+0x6c/0x80
>  dump_stack+0x14/0x1c
>  of_node_release+0x11c/0x188
>  kobject_cleanup+0x48/0x17c
>  kobject_put+0x78/0xc0
>  of_node_put+0x14/0x20
>  drm_of_find_panel_or_bridge+0x84/0xd4
>  devm_drm_of_get_bridge+0x3c/0x8c
>  lcdif_attach_bridge+0x88/0x270
>  lcdif_load+0x144/0x28c
>  lcdif_probe+0x34/0xcc
>  platform_probe+0x64/0xe8
>  really_probe+0xc8/0x3ac
>  __driver_probe_device+0x84/0x188
>  driver_probe_device+0x38/0x150
>  __device_attach_driver+0xcc/0x194
>  bus_for_each_drv+0x80/0xdc
>  __device_attach+0x9c/0x1d0
>  device_initial_probe+0x10/0x18
>  bus_probe_device+0xa4/0xa8
>  deferred_probe_work_func+0x9c/0xe8
>  process_one_work+0x154/0x3fc
>  worker_thread+0x2f4/0x404
>  kthread+0xf4/0x100
>  ret_from_fork+0x10/0x20
> OF: ERROR: next of_node_put() on this node will result in a kobject warni=
ng 'refcount_t: underflow; use-after-free.'
> ------------[ cut here ]------------
> refcount_t: addition on 0; use-after-free.
> WARNING: CPU: 0 PID: 11 at lib/refcount.c:25 refcount_warn_saturate+0x150=
/0x214
> Modules linked in:
> CPU: 0 PID: 11 Comm: kworker/u16:0 Not tainted 6.10.0-rc1-next-20240529+ =
#2511 610eecbb638fc5fab9a27e01b78203e8a379a280
> Hardware name: TQ-Systems i.MX8MPlus TQMa8MPxL on MBa8MPxL (DT)
> [...]
>
>  drivers/of/property.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 83536216ed4fe..e5c6301643e4c 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -836,9 +836,7 @@ struct device_node *of_graph_get_remote_node(const st=
ruct device_node *node,
>  {
>         struct device_node *endpoint_node __free(device_node) =3D
>                             of_graph_get_endpoint_by_regs(node, port, end=
point);
> -
> -       struct device_node *remote __free(device_node) =3D
> -                           of_graph_get_remote_port_parent(endpoint_node=
);
> +       struct device_node *remote;
>
>         if (!endpoint_node) {
>                 pr_debug("no valid endpoint (%d, %d) for node %pOF\n",
> @@ -846,6 +844,7 @@ struct device_node *of_graph_get_remote_node(const st=
ruct device_node *node,
>                 return NULL;
>         }
>
> +       remote =3D of_graph_get_remote_port_parent(endpoint_node);
>         if (!remote) {
>                 pr_debug("no valid remote node\n");
>                 return NULL;
> @@ -853,6 +852,7 @@ struct device_node *of_graph_get_remote_node(const st=
ruct device_node *node,
>
>         if (!of_device_is_available(remote)) {
>                 pr_debug("not available for remote node\n");
> +               of_node_put(remote);
>                 return NULL;
>         }
>
> --
> 2.34.1
>