+ liveupdate-defer-flb-module-refcounting-to-active-sessions.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: liveupdate: defer FLB module refcounting to active sessions
has been added to the -mm mm-new branch.  Its filename is
     liveupdate-defer-flb-module-refcounting-to-active-sessions.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/liveupdate-defer-flb-module-refcounting-to-active-sessions.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Pasha Tatashin <pasha.tatashin@soleen.com>
Subject: liveupdate: defer FLB module refcounting to active sessions
Date: Wed, 18 Mar 2026 10:16:42 -0400

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://lkml.kernel.org/r/20260318141637.1870220-14-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: David Matlack <dmatlack@google.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/liveupdate/luo_flb.c |   27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

--- a/kernel/liveupdate/luo_flb.c~liveupdate-defer-flb-module-refcounting-to-active-sessions
+++ a/kernel/liveupdate/luo_flb.c
@@ -112,10 +112,15 @@ static int luo_flb_file_preserve_one(str
 			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;
 		}
@@ -143,6 +148,7 @@ static void luo_flb_file_unpreserve_one(
 
 			private->outgoing.data = 0;
 			private->outgoing.obj = NULL;
+			module_put(flb->ops->owner);
 		}
 	}
 }
@@ -178,12 +184,17 @@ static int luo_flb_retrieve_one(struct l
 	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;
@@ -217,6 +228,7 @@ static void luo_flb_file_finish_one(stru
 			private->incoming.data = 0;
 			private->incoming.obj = NULL;
 			private->incoming.finished = true;
+			module_put(flb->ops->owner);
 		}
 	}
 }
@@ -394,11 +406,6 @@ int liveupdate_register_flb(struct liveu
 				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++;
 	}
@@ -474,12 +481,11 @@ int liveupdate_unregister_flb(struct liv
 	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);
 	}
 
 	luo_session_resume();
@@ -506,7 +512,8 @@ 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)
 {
_

Patches currently in -mm which might be from pasha.tatashin@soleen.com are

mm-vmalloc-export-clear_vm_uninitialized_flag.patch
kho-fix-kasan-support-for-restored-vmalloc-regions.patch
liveupdate-protect-file-handler-list-with-rwsem.patch
liveupdate-protect-flb-lists-with-rwsem.patch
liveupdate-remove-file-handler-module-refcounting.patch
liveupdate-defer-flb-module-refcounting-to-active-sessions.patch
liveupdate-remove-luo_session_quiesce.patch
liveupdate-auto-unregister-flbs-on-file-handler-unregistration.patch
liveupdate-remove-liveupdate_test_unregister.patch
liveupdate-make-unregister-functions-return-void.patch