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Message-ID: <20250902132900.GN2163762@google.com>
Date: Tue, 2 Sep 2025 14:29:00 +0100
From: Lee Jones <lee@...nel.org>
To: Bastien Curutchet <bastien.curutchet@...tlin.com>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Miquèl Raynal <miquel.raynal@...tlin.com>,
Cheng Ming Lin <linchengming884@...il.com>,
Cheng Ming Lin <chengminglin@...c.com.tw>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mfd: core: Increment of_node's refcount before linking
it to the platform device
On Wed, 20 Aug 2025, Bastien Curutchet wrote:
> When an MFD device is added, a platform_device is allocated. If this
> device is linked to a DT description, the corresponding OF node is linked
> to the new platform device but the OF node's refcount isn't incremented.
> As of_node_put() is called during the platform device release, it leads
> to a refcount underflow.
>
> Call of_node_get() to increment the OF node's refcount when the node is
> linked to the newly created platform device.
>
> Signed-off-by: Bastien Curutchet <bastien.curutchet@...tlin.com>
> ---
> Hi all,
>
> I'm currently working on a new MFD driver and I encountered some
> underflow errors with the of_node refcount. As you can see in the logs
> below, I reproduced the issue on a mainline driver (atmel-hlcdc):
>
> > # modprobe atmel-hlcdc
> > # modprobe -r atmel-hlcdc
> > # modprobe atmel-hlcdc
> > # modprobe -r atmel-hlcdc
> > [ 22.932128] OF: ERROR: of_node_release() detected bad of_node_put() on /amba_pl/atmel_sama5@...00000/dc
> > [ 22.941586] CPU: 1 UID: 0 PID: 103 Comm: modprobe Not tainted 6.17.0-rc2-00053-gb19a97d57c15-dirty #81 NONE
> > [ 22.941608] Hardware name: Xilinx Zynq Platform
> > [ 22.941615] Call trace:
> > [ 22.941626] unwind_backtrace from show_stack+0x10/0x14
> > [ 22.941660] show_stack from dump_stack_lvl+0x54/0x68
> > [ 22.941680] dump_stack_lvl from of_node_release+0x140/0x16c
> > [ 22.941707] of_node_release from kobject_put+0x110/0x130
> > [ 22.941745] kobject_put from platform_device_release+0x10/0x3c
> > [ 22.941782] platform_device_release from device_release+0x30/0xa0
> > [ 22.941814] device_release from kobject_put+0x88/0x130
> > [ 22.941845] kobject_put from klist_prev+0xd4/0x16c
> > [ 22.941879] klist_prev from device_for_each_child_reverse+0x88/0xc8
> > [ 22.941911] device_for_each_child_reverse from devm_mfd_dev_release+0x30/0x54
> > [ 22.941941] devm_mfd_dev_release from devres_release_all+0xb0/0x114
> > [ 22.941974] devres_release_all from device_unbind_cleanup+0xc/0x58
> > [ 22.942003] device_unbind_cleanup from device_release_driver_internal+0x190/0x1c4
> > [ 22.942025] device_release_driver_internal from driver_detach+0x54/0xa0
> > [ 22.942046] driver_detach from bus_remove_driver+0x58/0xa4
> > [ 22.942066] bus_remove_driver from sys_delete_module+0x178/0x25c
> > [ 22.942094] sys_delete_module from ret_fast_syscall+0x0/0x54
> > [ 22.942116] Exception stack(0xf0a1dfa8 to 0xf0a1dff0)
> > [ 22.942130] dfa0: 004ec438 005a0870 005a0d40 00000080 00000000 005a0d18
> > [ 22.942144] dfc0: 004ec438 005a0870 005a0190 00000081 005a0d60 005a0870 00000001 0059f6bc
> > [ 22.942155] dfe0: beccdb20 beccdb10 004ed1f4 b6e9eb40
> > [ 22.942163] OF: ERROR: next of_node_put() on this node will result in a kobject warning 'refcount_t: underflow; use-after-free.'
> > [ 23.098617] OF: ERROR: of_node_release() detected bad of_node_put() on /amba_pl/atmel_sama5@...00000/pwm
> > [ 23.108137] CPU: 1 UID: 0 PID: 103 Comm: modprobe Not tainted 6.17.0-rc2-00053-gb19a97d57c15-dirty #81 NONE
> > [ 23.108159] Hardware name: Xilinx Zynq Platform
> > [ 23.108166] Call trace:
> > [ 23.108173] unwind_backtrace from show_stack+0x10/0x14
> > [ 23.108206] show_stack from dump_stack_lvl+0x54/0x68
> > [ 23.108227] dump_stack_lvl from of_node_release+0x140/0x16c
> > [ 23.108252] of_node_release from kobject_put+0x110/0x130
> > [ 23.108288] kobject_put from platform_device_release+0x10/0x3c
> > [ 23.108324] platform_device_release from device_release+0x30/0xa0
> > [ 23.108354] device_release from kobject_put+0x88/0x130
> > [ 23.108384] kobject_put from klist_prev+0xd4/0x16c
> > [ 23.108418] klist_prev from device_for_each_child_reverse+0x88/0xc8
> > [ 23.108450] device_for_each_child_reverse from devm_mfd_dev_release+0x30/0x54
> > [ 23.108479] devm_mfd_dev_release from devres_release_all+0xb0/0x114
> > [ 23.108513] devres_release_all from device_unbind_cleanup+0xc/0x58
> > [ 23.108541] device_unbind_cleanup from device_release_driver_internal+0x190/0x1c4
> > [ 23.108563] device_release_driver_internal from driver_detach+0x54/0xa0
> > [ 23.108585] driver_detach from bus_remove_driver+0x58/0xa4
> > [ 23.108605] bus_remove_driver from sys_delete_module+0x178/0x25c
> > [ 23.108631] sys_delete_module from ret_fast_syscall+0x0/0x54
> > [ 23.108653] Exception stack(0xf0a1dfa8 to 0xf0a1dff0)
> > [ 23.108667] dfa0: 004ec438 005a0870 005a0d40 00000080 00000000 005a0d18
> > [ 23.108681] dfc0: 004ec438 005a0870 005a0190 00000081 005a0d60 005a0870 00000001 0059f6bc
> > [ 23.108691] dfe0: beccdb20 beccdb10 004ed1f4 b6e9eb40
> > [ 23.108698] OF: ERROR: next of_node_put() on this node will result in a kobject warning 'refcount_t: underflow; use-after-free.'
> ---
> drivers/mfd/mfd-core.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> index 76bd316a50afc5c07ff2a3303c4363b16d0bc023..7d14a1e7631ee8d5e91b228a07b2d05695e41b6e 100644
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -131,6 +131,7 @@ static int mfd_match_of_node_to_dev(struct platform_device *pdev,
> of_entry->np = np;
> list_add_tail(&of_entry->list, &mfd_of_node_list);
>
> + of_node_get(np);
Looks okay at first blush.
My question would be, why isn't this required for all calls to device_set_node()?
> device_set_node(&pdev->dev, of_fwnode_handle(np));
> #endif
> return 0;
>
> ---
> base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
> change-id: 20250820-mfd-refcount-0d561c25b10b
>
> Best regards,
> --
> Bastien Curutchet <bastien.curutchet@...tlin.com>
>
--
Lee Jones [李琼斯]
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