Re: [PATCH v3 05/10] liveupdate: Defer FLB module refcounting to active sessions

[Samiullah Khawaja <skhawaja@google.com>]

On Fri, Mar 27, 2026 at 03:33:29AM +0000, Pasha Tatashin wrote:
>Stop pinning modules indefinitely upon FLB registration.
>Instead, dynamically take a module reference when the FLB is actively
>used in a session (e.g., during preserve and retrieve) and release it
>when the session concludes.
>
>This allows modules providing FLB operations to be cleanly unloaded
>when not in active use by the live update orchestrator.
>
>Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
>---
> kernel/liveupdate/luo_flb.c | 27 +++++++++++++++++----------
> 1 file changed, 17 insertions(+), 10 deletions(-)
>
>diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
>index 3c91d0008eb1..ce28ce9b113e 100644
>--- a/kernel/liveupdate/luo_flb.c
>+++ b/kernel/liveupdate/luo_flb.c
>@@ -115,10 +115,15 @@ static int luo_flb_file_preserve_one(struct liveupdate_flb *flb)
> 			struct liveupdate_flb_op_args args = {0};
> 			int err;
>
>+			if (!try_module_get(flb->ops->owner))
>+				return -ENODEV;
>+
> 			args.flb = flb;
> 			err = flb->ops->preserve(&args);
>-			if (err)
>+			if (err) {
>+				module_put(flb->ops->owner);
> 				return err;
>+			}
> 			private->outgoing.data = args.data;
> 			private->outgoing.obj = args.obj;
> 		}
>@@ -146,6 +151,7 @@ static void luo_flb_file_unpreserve_one(struct liveupdate_flb *flb)
>
> 			private->outgoing.data = 0;
> 			private->outgoing.obj = NULL;
>+			module_put(flb->ops->owner);
> 		}
> 	}
> }
>@@ -181,12 +187,17 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
> 	if (!found)
> 		return -ENOENT;
>
>+	if (!try_module_get(flb->ops->owner))
>+		return -ENODEV;
>+
> 	args.flb = flb;
> 	args.data = private->incoming.data;
>
> 	err = flb->ops->retrieve(&args);
>-	if (err)
>+	if (err) {
>+		module_put(flb->ops->owner);
> 		return err;
>+	}
>
> 	private->incoming.obj = args.obj;
> 	private->incoming.retrieved = true;
>@@ -237,6 +248,7 @@ static void luo_flb_file_finish_one(struct liveupdate_flb *flb)
> 			private->incoming.data = 0;
> 			private->incoming.obj = NULL;
> 			private->incoming.finished = true;
>+			module_put(flb->ops->owner);
> 		}
> 	}
> }
>@@ -412,11 +424,6 @@ int liveupdate_register_flb(struct liveupdate_file_handler *fh,
> 				goto err_resume;
> 		}
>
>-		if (!try_module_get(flb->ops->owner)) {
>-			err = -EAGAIN;
>-			goto err_resume;
>-		}
>-
> 		list_add_tail(&private->list, &luo_flb_global.list);
> 		luo_flb_global.count++;
> 	}
>@@ -493,12 +500,11 @@ int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
> 	private->users--;
> 	/*
> 	 * If this is the last file-handler with which we are registred, remove
>-	 * from the global list, and relese module reference.
>+	 * from the global list.
> 	 */
> 	if (!private->users) {
> 		list_del_init(&private->list);
> 		luo_flb_global.count--;
>-		module_put(flb->ops->owner);
> 	}
>
> 	up_write(&luo_register_rwlock);
>@@ -527,7 +533,8 @@ int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
>  *
>  * Return: 0 on success, or a negative errno on failure. -ENODATA means no
>  * incoming FLB data, -ENOENT means specific flb not found in the incoming
>- * data, and -EOPNOTSUPP when live update is disabled or not configured.
>+ * data, -ENODEV if the FLB's module is unloading, and -EOPNOTSUPP when
>+ * live update is disabled or not configured.
>  */
> int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp)
> {
>-- 
>2.43.0
>

Reviewed-by: Samiullah Khawaja <skhawaja@google.com>