[PATCH 5/6] liveupdate: Make unregister functions return void

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

Change liveupdate_unregister_file_handler and liveupdate_unregister_flb
to return void instead of an error code. If they fail to unregister
due to dangling references, print a warning instead of aborting.

As pointed out by Jason Gunthorpe and Alex Williamson, returning an error
from a "destroy" or unregister function during a module unload is a poor
API choice since the unload cannot be stopped at that point.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 include/linux/liveupdate.h   | 13 ++++++------
 kernel/liveupdate/luo_file.c | 27 +++++++++++-------------
 kernel/liveupdate/luo_flb.c  | 40 ++++++++++--------------------------
 lib/tests/liveupdate.c       |  8 ++------
 4 files changed, 31 insertions(+), 57 deletions(-)

diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
index 8394fb2d8774..293df26b9e7f 100644
--- a/include/linux/liveupdate.h
+++ b/include/linux/liveupdate.h
@@ -231,12 +231,12 @@ bool liveupdate_enabled(void);
 int liveupdate_reboot(void);
 
 int liveupdate_register_file_handler(struct liveupdate_file_handler *fh);
-int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh);
+void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh);
 
 int liveupdate_register_flb(struct liveupdate_file_handler *fh,
 			    struct liveupdate_flb *flb);
-int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
-			      struct liveupdate_flb *flb);
+void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
+			       struct liveupdate_flb *flb);
 
 int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp);
 int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp);
@@ -258,9 +258,8 @@ static inline int liveupdate_register_file_handler(struct liveupdate_file_handle
 	return -EOPNOTSUPP;
 }
 
-static inline int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
+static inline void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
 {
-	return -EOPNOTSUPP;
 }
 
 static inline int liveupdate_register_flb(struct liveupdate_file_handler *fh,
@@ -269,8 +268,8 @@ static inline int liveupdate_register_flb(struct liveupdate_file_handler *fh,
 	return -EOPNOTSUPP;
 }
 
-static inline int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
-					    struct liveupdate_flb *flb)
+static inline void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
+					     struct liveupdate_flb *flb)
 {
 	return -EOPNOTSUPP;
 }
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 6b2b49cb375e..0fe2f8be8bd1 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -907,21 +907,17 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
  * reverses the operations of liveupdate_register_file_handler().
  *
  * It ensures safe removal by checking that:
- * No live update session is currently in progress.
  * No FLB registered with this file handler.
  *
  * If the unregistration fails, the internal test state is reverted.
  *
- * Return: 0 Success. -EOPNOTSUPP when live update is not enabled. -EBUSY A live
- * update is in progress, can't quiesce live update or FLB is registred with
- * this file handler.
  */
-int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
+void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
 {
-	int err = -EBUSY;
+	bool is_empty;
 
 	if (!liveupdate_enabled())
-		return -EOPNOTSUPP;
+		return;
 
 	liveupdate_test_unregister(fh);
 
@@ -929,18 +925,19 @@ int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
 		goto err_register;
 
 	scoped_guard(rwsem_write, &luo_file_handler_lock) {
-		if (!list_empty(&ACCESS_PRIVATE(fh, flb_list)))
-			goto err_resume;
-
-		list_del(&ACCESS_PRIVATE(fh, list));
+		is_empty = list_empty(&ACCESS_PRIVATE(fh, flb_list));
+		if (is_empty)
+			list_del(&ACCESS_PRIVATE(fh, list));
 	}
 	luo_session_resume();
 
-	return 0;
+	if (!is_empty) {
+		pr_warn("Failed to unregister file handler '%s': FLB list not empty\n",
+			fh->compatible);
+		liveupdate_test_register(fh);
+	}
+	return;
 
-err_resume:
-	luo_session_resume();
 err_register:
 	liveupdate_test_register(fh);
-	return err;
 }
diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index daa852abdedd..23fa6e0c6083 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -436,31 +436,17 @@ int liveupdate_register_flb(struct liveupdate_file_handler *fh,
  * the FLB is removed from the global registry and the reference to its
  * owner module (acquired during registration) is released.
  *
- * Context: This function ensures the session is quiesced (no active FDs
- *          being created) during the update. It is typically called from a
- *          subsystem's module exit function.
- * Return: 0 on success.
- *         -EOPNOTSUPP if live update is disabled.
- *         -EBUSY if the live update session is active and cannot be quiesced.
- *         -ENOENT if the FLB was not found in the file handler's list.
  */
-int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
-			      struct liveupdate_flb *flb)
+void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
+			       struct liveupdate_flb *flb)
 {
 	struct luo_flb_private *private = luo_flb_get_private(flb);
 	struct list_head *flb_list = &ACCESS_PRIVATE(fh, flb_list);
 	struct luo_flb_link *iter;
-	int err = -ENOENT;
+	bool found = false;
 
 	if (!liveupdate_enabled())
-		return -EOPNOTSUPP;
-
-	/*
-	 * Ensure the system is quiescent (no active sessions).
-	 * This acts as a global lock for unregistration.
-	 */
-	if (!luo_session_quiesce())
-		return -EBUSY;
+		return;
 
 	guard(rwsem_write)(&luo_flb_lock);
 	guard(rwsem_write)(&ACCESS_PRIVATE(fh, flb_lock));
@@ -470,15 +456,19 @@ int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
 		if (iter->flb == flb) {
 			list_del(&iter->list);
 			kfree(iter);
-			err = 0;
+			found = true;
 			break;
 		}
 	}
 
-	if (err)
-		goto err_resume;
+	if (!found) {
+		pr_warn("Failed to unregister FLB '%s': not found in file handler '%s'\n",
+			flb->compatible, fh->compatible);
+		return;
+	}
 
 	private->users--;
+
 	/*
 	 * If this is the last file-handler with which we are registred, remove
 	 * from the global list, and relese module reference.
@@ -487,14 +477,6 @@ int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
 		list_del_init(&private->list);
 		luo_flb_global.count--;
 	}
-
-	luo_session_resume();
-
-	return 0;
-
-err_resume:
-	luo_session_resume();
-	return err;
 }
 
 /**
diff --git a/lib/tests/liveupdate.c b/lib/tests/liveupdate.c
index 496d6ef91a30..5b6abf779f87 100644
--- a/lib/tests/liveupdate.c
+++ b/lib/tests/liveupdate.c
@@ -137,16 +137,12 @@ void liveupdate_test_register(struct liveupdate_file_handler *fh)
 
 void liveupdate_test_unregister(struct liveupdate_file_handler *fh)
 {
-	int err, i;
+	int i;
 
 	for (i = 0; i < TEST_NFLBS; i++) {
 		struct liveupdate_flb *flb = &test_flbs[i];
 
-		err = liveupdate_unregister_flb(fh, flb);
-		if (err) {
-			pr_err("Failed to unregister %s %pe\n",
-			       flb->compatible, ERR_PTR(err));
-		}
+		liveupdate_unregister_flb(fh, flb);
 	}
 
 	pr_info("Unregistered %d FLBs from file handler: [%s]\n",
-- 
2.53.0.851.ga537e3e6e9-goog