liveupdate: defer FLB module refcounting to active sessions

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.

Link: https://lore.kernel.org/20260327033335.696621-6-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Reviewed-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Cc: David Matlack <dmatlack@google.com>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index fdb274410e8fcb8f1daf1182abe8834a64386334..3d439d1c8ff111680eabf6c9d85f146e80d3a02b 100644 (file)
--- 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;
@@ -220,6 +231,7 @@ 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);
                }
        }
 }
@@ -395,11 +407,6 @@ 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++;
        }
@@ -476,12 +483,11 @@ 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);
@@ -510,7 +516,8 @@ err_resume:
  *
  * 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)
 {