[PATCH 3/6] 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>
---
 kernel/liveupdate/luo_file.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 6a0ae29c6a24..6b2b49cb375e 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -253,6 +253,7 @@ static bool luo_token_is_used(struct luo_file_set *file_set, u64 token)
  *         -ENOSPC if the file_set is full.
  *         -ENOENT if no compatible handler is found.
  *         -ENOMEM on memory allocation failure.
+ *         -ENODEV if the file handler's module is unloading.
  *         Other erros might be returned by .preserve().
  */
 int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
@@ -281,7 +282,10 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	scoped_guard(rwsem_read, &luo_file_handler_lock) {
 		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;
+				else
+					err = -ENODEV;
 				break;
 			}
 		}
@@ -293,7 +297,7 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 
 	err = luo_flb_file_preserve(fh);
 	if (err)
-		goto err_free_files_mem;
+		goto err_module_put;
 
 	luo_file = kzalloc_obj(*luo_file);
 	if (!luo_file) {
@@ -323,6 +327,8 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	kfree(luo_file);
 err_flb_unpreserve:
 	luo_flb_file_unpreserve(fh);
+err_module_put:
+	module_put(fh->ops->owner);
 err_free_files_mem:
 	luo_free_files_mem(file_set);
 err_fput:
@@ -365,6 +371,7 @@ 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);
 
 		list_del(&luo_file->list);
 		file_set->count--;
@@ -649,6 +656,7 @@ 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);
 }
 
 /**
@@ -783,7 +791,8 @@ int luo_file_deserialize(struct luo_file_set *file_set,
 		scoped_guard(rwsem_read, &luo_file_handler_lock) {
 			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;
 				}
 			}
@@ -796,8 +805,10 @@ 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;
@@ -873,6 +884,7 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
 		}
 
 		INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, flb_list));
+		init_rwsem(&ACCESS_PRIVATE(fh, flb_lock));
 		INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, list));
 		list_add_tail(&ACCESS_PRIVATE(fh, list), &luo_file_handler_list);
 	}
@@ -922,7 +934,6 @@ int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
 
 		list_del(&ACCESS_PRIVATE(fh, list));
 	}
-	module_put(fh->ops->owner);
 	luo_session_resume();
 
 	return 0;
-- 
2.53.0.851.ga537e3e6e9-goog