[PATCH v2] extcon: Fixed sysfs duplicate filename issue

[PATCH v2] extcon: Fixed sysfs duplicate filename issue

[Michael Wu]

With current extcon_dev_unregister() timing, ida_free is before
device_unregister(), that may cause current id re-alloc to another
device in extcon_dev_register() context but sysfs filename path not
removal completed yet.

The right timing shows below:
on extcon_dev_register: ida_alloc() -> device_register()
on extcon_dev_unregister: device_unregister() -> ida_free()

stack information when an error occurs:
sysfs: cannot create duplicate filename '/class/extcon/extcon1'
Call trace:
 dump_backtrace+0xe8/0x108
 show_stack+0x18/0x28
 dump_stack_lvl+0x50/0x6c
 dump_stack+0x18/0x24
 sysfs_warn_dup+0x68/0x88
 sysfs_do_create_link_sd+0x94/0xdc
 sysfs_create_link+0x30/0x48
 device_add_class_symlinks+0xb4/0x12c
 device_add+0x1e0/0x48c
 device_register+0x20/0x34
 extcon_dev_register+0x3b8/0x5c4
 devm_extcon_dev_register+0x4c/0x94

Fixes: 7bba9e81a6fb ("extcon: Use unique number for the extcon device ID")
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Michael Wu <michael@allwinnertech.com>
---
ChangeLog:
V1 -> V2: Update commit msg, suggested by Markus Elfring
V1: https://lore.kernel.org/all/20251011053719.87055-1-michael@allwinnertech.com/
---
---
 drivers/extcon/extcon.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/extcon/extcon.c b/drivers/extcon/extcon.c
index e7f55c021e562..c08f642d7f5ee 100644
--- a/drivers/extcon/extcon.c
+++ b/drivers/extcon/extcon.c
@@ -1371,10 +1371,10 @@ void extcon_dev_unregister(struct extcon_dev *edev)
 		return;
 	}
 
-	ida_free(&extcon_dev_ids, edev->id);
-
 	device_unregister(&edev->dev);
 
+	ida_free(&extcon_dev_ids, edev->id);
+
 	if (edev->mutually_exclusive && edev->max_supported) {
 		for (index = 0; edev->mutually_exclusive[index];
 				index++)
-- 
2.29.0

Re: [PATCH v2] extcon: Fixed sysfs duplicate filename issue

[Andy Shevchenko]

On Wed, Oct 15, 2025 at 02:51:02PM +0800, Michael Wu wrote:

Thank you for a fix, my comments below.

> With current extcon_dev_unregister() timing, ida_free is before
> device_unregister(), that may cause current id re-alloc to another
> device in extcon_dev_register() context but sysfs filename path not
> removal completed yet.
> 
> The right timing shows below:
> on extcon_dev_register: ida_alloc() -> device_register()
> on extcon_dev_unregister: device_unregister() -> ida_free()
> 
> stack information when an error occurs:
> sysfs: cannot create duplicate filename '/class/extcon/extcon1'
> Call trace:

>  dump_backtrace+0xe8/0x108
>  show_stack+0x18/0x28
>  dump_stack_lvl+0x50/0x6c
>  dump_stack+0x18/0x24

At least these four lines are noisy in the commit message. The Submitting
Patches documentation recommends to leave ~3-5 important lines out of a trace
back, so the below is okay in my opinion, except the last line also can be
dropped (devm call).

>  sysfs_warn_dup+0x68/0x88
>  sysfs_do_create_link_sd+0x94/0xdc
>  sysfs_create_link+0x30/0x48
>  device_add_class_symlinks+0xb4/0x12c
>  device_add+0x1e0/0x48c
>  device_register+0x20/0x34
>  extcon_dev_register+0x3b8/0x5c4
>  devm_extcon_dev_register+0x4c/0x94

> Fixes: 7bba9e81a6fb ("extcon: Use unique number for the extcon device ID")
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Better to reduce a noise in the Git history by moving the Cc:s to the...

> Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
> Signed-off-by: Michael Wu <michael@allwinnertech.com>
> ---

...comment block here. It will have the same effect on the emails (tools will
Cc people listed here).

> ChangeLog:
> V1 -> V2: Update commit msg, suggested by Markus Elfring
> V1: https://lore.kernel.org/all/20251011053719.87055-1-michael@allwinnertech.com/

Code wise LGTM, FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko