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

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On Mon, Mar 30, 2026 at 12:56 PM Samiullah Khawaja <skhawaja@google.com> wrote:
>
> 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>

Thank you Sami.

Pasha