linux-kernel - RE: [PATCH net] dpll: Prevent duplicate registrations

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Message-ID: <LV4PR11MB9491BC664A5ADA3D0DA7F1559B96A@LV4PR11MB9491.namprd11.prod.outlook.com>
Date: Wed, 21 Jan 2026 13:37:35 +0000
From: "Kubalewski, Arkadiusz" <arkadiusz.kubalewski@...el.com>
To: "Vecera, Ivan" <ivecera@...hat.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
CC: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, Jiri Pirko
	<jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>, Michal Michalik
	<michal.michalik@...el.com>, "Olech, Milena" <milena.olech@...el.com>, "open
 list" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net] dpll: Prevent duplicate registrations

>From: Ivan Vecera <ivecera@...hat.com>
>Sent: Wednesday, January 21, 2026 2:00 PM
>
>Modify the internal registration helpers dpll_xa_ref_{dpll,pin}_add()
>to reject duplicate registration attempts.
>
>Previously, if a caller attempted to register the same pin multiple
>times (with the same ops, priv, and cookie) on the same device, the core
>silently increments the reference count and return success. This behavior
>is incorrect because if the caller makes these duplicate registrations
>then for the first one dpll_pin_registration is allocated and for others
>the associated dpll_pin_ref.refcount is incremented. During the first
>unregistration the associated dpll_pin_registration is freed and for
>others WARN is fired.
>
>Fix this by updating the logic to return `-EEXIST` if a matching
>registration is found to enforce a strict "register once" policy.
>
>Fixes: 9431063ad323 ("dpll: core: Add DPLL framework base functions")
>Signed-off-by: Ivan Vecera <ivecera@...hat.com>
>---
> drivers/dpll/dpll_core.c | 12 ++++--------
> 1 file changed, 4 insertions(+), 8 deletions(-)
>
>diff --git a/drivers/dpll/dpll_core.c b/drivers/dpll/dpll_core.c
>index a461095efd8a..8879a7235156 100644
>--- a/drivers/dpll/dpll_core.c
>+++ b/drivers/dpll/dpll_core.c
>@@ -83,10 +83,8 @@ dpll_xa_ref_pin_add(struct xarray *xa_pins, struct
>dpll_pin *pin,
> 		if (ref->pin != pin)
> 			continue;
> 		reg = dpll_pin_registration_find(ref, ops, priv, cookie);
>-		if (reg) {
>-			refcount_inc(&ref->refcount);
>-			return 0;
>-		}
>+		if (reg)
>+			return -EEXIST;
> 		ref_exists = true;
> 		break;
> 	}
>@@ -164,10 +162,8 @@ dpll_xa_ref_dpll_add(struct xarray *xa_dplls, struct
>dpll_device *dpll,
> 		if (ref->dpll != dpll)
> 			continue;
> 		reg = dpll_pin_registration_find(ref, ops, priv, cookie);
>-		if (reg) {
>-			refcount_inc(&ref->refcount);
>-			return 0;
>-		}
>+		if (reg)
>+			return -EEXIST;
> 		ref_exists = true;
> 		break;
> 	}
>--
>2.52.0

Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>