liveupdate: defer file handler module refcounting to active sessions

Stop pinning modules indefinitely upon file handler registration.
Instead, dynamically increment the module reference count only when a live
update session actively uses the file handler (e.g., during preservation
or deserialization), and release it when the session ends.

This allows modules providing live update handlers to be gracefully
unloaded when no live update is in progress.

Link: https://lore.kernel.org/20260327033335.696621-11-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Cc: David Matlack <dmatlack@google.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Samiullah Khawaja <skhawaja@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 0730865711c11ec6894f596a2d5efd13a118df23..a0a419085e2830a20d37f920a8d157d6453d3823 100644 (file)
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -291,7 +291,8 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
        down_read(&luo_register_rwlock);
        list_private_for_each_entry(fh, &luo_file_handler_list, list) {
                if (fh->ops->can_preserve(fh, file)) {
-                       err = 0;
+                       if (try_module_get(fh->ops->owner))
+                               err = 0;
                        break;
                }
        }
@@ -304,7 +305,7 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
        err = xa_insert(&luo_preserved_files, luo_get_id(fh, file),
                        file, GFP_KERNEL);
        if (err)
-               goto err_free_files_mem;
+               goto err_module_put;
 
        err = luo_flb_file_preserve(fh);
        if (err)
@@ -340,6 +341,8 @@ err_flb_unpreserve:
        luo_flb_file_unpreserve(fh);
 err_erase_xa:
        xa_erase(&luo_preserved_files, luo_get_id(fh, file));
+err_module_put:
+       module_put(fh->ops->owner);
 err_free_files_mem:
        luo_free_files_mem(file_set);
 err_fput:
@@ -382,6 +385,7 @@ void luo_file_unpreserve_files(struct luo_file_set *file_set)
                args.private_data = luo_file->private_data;
                luo_file->fh->ops->unpreserve(&args);
                luo_flb_file_unpreserve(luo_file->fh);
+               module_put(luo_file->fh->ops->owner);
 
                xa_erase(&luo_preserved_files,
                         luo_get_id(luo_file->fh, luo_file->file));
@@ -673,6 +677,7 @@ static void luo_file_finish_one(struct luo_file_set *file_set,
 
        luo_file->fh->ops->finish(&args);
        luo_flb_file_finish(luo_file->fh);
+       module_put(luo_file->fh->ops->owner);
 }
 
 /**
@@ -810,7 +815,8 @@ int luo_file_deserialize(struct luo_file_set *file_set,
                down_read(&luo_register_rwlock);
                list_private_for_each_entry(fh, &luo_file_handler_list, list) {
                        if (!strcmp(fh->compatible, file_ser[i].compatible)) {
-                               handler_found = true;
+                               if (try_module_get(fh->ops->owner))
+                                       handler_found = true;
                                break;
                        }
                }
@@ -824,8 +830,10 @@ int luo_file_deserialize(struct luo_file_set *file_set,
                }
 
                luo_file = kzalloc_obj(*luo_file);
-               if (!luo_file)
+               if (!luo_file) {
+                       module_put(fh->ops->owner);
                        return -ENOMEM;
+               }
 
                luo_file->fh = fh;
                luo_file->file = NULL;
@@ -886,12 +894,6 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
                }
        }
 
-       /* Pin the module implementing the handler */
-       if (!try_module_get(fh->ops->owner)) {
-               err = -EAGAIN;
-               goto err_unlock;
-       }
-
        INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, flb_list));
        INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, list));
        list_add_tail(&ACCESS_PRIVATE(fh, list), &luo_file_handler_list);
@@ -921,6 +923,4 @@ void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
        guard(rwsem_write)(&luo_register_rwlock);
        luo_flb_unregister_all(fh);
        list_del(&ACCESS_PRIVATE(fh, list));
-
-       module_put(fh->ops->owner);
 }