[PATCH v4 10/11] liveupdate: Defer file handler module refcounting to active sessions

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

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.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 kernel/liveupdate/luo_file.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index f8e098858c62..dedbb8d02e6a 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -292,7 +292,8 @@ 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;
 		}
 	}
@@ -306,7 +307,7 @@ 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)
@@ -342,6 +343,8 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	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:
@@ -384,6 +387,7 @@ 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));
@@ -675,6 +679,7 @@ 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);
 }
 
 /**
@@ -812,7 +817,8 @@ 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;
 			}
 		}
@@ -826,8 +832,10 @@ 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;
+		}
 
 		/* safe to use fh because its module is pinned */
 		luo_file->fh = fh;
@@ -889,12 +897,6 @@ 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);
@@ -924,6 +926,4 @@ 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);
 }
-- 
2.43.0