kho: drop notifiers

The KHO framework uses a notifier chain as the mechanism for clients to
participate in the finalization process.  While this works for a single,
central state machine, it is too restrictive for kernel-internal
components like pstore/reserve_mem or IMA.  These components need a
simpler, direct way to register their state for preservation (e.g., during
their initcall) without being part of a complex, shutdown-time notifier
sequence.  The notifier model forces all participants into a single
finalization flow and makes direct preservation from an arbitrary context
difficult.  This patch refactors the client participation model by
removing the notifier chain and introducing a direct API for managing FDT
subtrees.

The core kho_finalize() and kho_abort() state machine remains, but clients
now register their data with KHO beforehand.

Link: https://lkml.kernel.org/r/20251101142325.1326536-3-pasha.tatashin@soleen.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Co-developed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Simon Horman <horms@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 3 insertions, 32 deletions

diff --git a/lib/test_kho.c b/lib/test_kho.c
index fff018e5548d..27618c5b4796 100644
--- a/lib/test_kho.c
+++ b/lib/test_kho.c
@@ -39,33 +39,6 @@ struct kho_test_state {
 
 static struct kho_test_state kho_test_state;
 
-static int kho_test_notifier(struct notifier_block *self, unsigned long cmd,
-			     void *v)
-{
-	struct kho_test_state *state = &kho_test_state;
-	struct kho_serialization *ser = v;
-	int err = 0;
-
-	switch (cmd) {
-	case KEXEC_KHO_ABORT:
-		return NOTIFY_DONE;
-	case KEXEC_KHO_FINALIZE:
-		/* Handled below */
-		break;
-	default:
-		return NOTIFY_BAD;
-	}
-
-	err |= kho_preserve_folio(state->fdt);
-	err |= kho_add_subtree(ser, KHO_TEST_FDT, folio_address(state->fdt));
-
-	return err ? NOTIFY_BAD : NOTIFY_DONE;
-}
-
-static struct notifier_block kho_test_nb = {
-	.notifier_call = kho_test_notifier,
-};
-
 static int kho_test_save_data(struct kho_test_state *state, void *fdt)
 {
 	phys_addr_t *folios_info __free(kvfree) = NULL;
@@ -120,6 +93,7 @@ static int kho_test_prepare_fdt(struct kho_test_state *state)
 
 	fdt = folio_address(state->fdt);
 
+	err |= kho_preserve_folio(state->fdt);
 	err |= fdt_create(fdt, fdt_size);
 	err |= fdt_finish_reservemap(fdt);
 
@@ -131,6 +105,7 @@ static int kho_test_prepare_fdt(struct kho_test_state *state)
 
 	err |= fdt_finish(fdt);
 
+	err = kho_add_subtree(KHO_TEST_FDT, folio_address(state->fdt));
 	if (err)
 		folio_put(state->fdt);
 
@@ -203,10 +178,6 @@ static int kho_test_save(void)
 	if (err)
 		goto err_free_folios;
 
-	err = register_kho_notifier(&kho_test_nb);
-	if (err)
-		goto err_free_fdt;
-
 	return 0;
 
 err_free_fdt:
@@ -329,7 +300,7 @@ static void kho_test_cleanup(void)
 
 static void __exit kho_test_exit(void)
 {
-	unregister_kho_notifier(&kho_test_nb);
+	kho_remove_subtree(folio_address(kho_test_state.fdt));
 	kho_test_cleanup();
 }
 module_exit(kho_test_exit);