Re: [PATCH v4 03/30] kho: drop notifiers

[Pratyush Yadav]

Hi,

On Mon, Oct 06 2025, Pratyush Yadav wrote:

> Hi Pasha,
>
> On Mon, Sep 29 2025, Pasha Tatashin wrote:
>
>> From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>
>>
>> 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.
>>
>> Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
>> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
>
> This patch breaks build of test_kho.c (under CONFIG_TEST_KEXEC_HANDOVER):
>
> 	lib/test_kho.c:49:14: error: ‘KEXEC_KHO_ABORT’ undeclared (first use in this function)
> 	   49 |         case KEXEC_KHO_ABORT:
> 	      |              ^~~~~~~~~~~~~~~
> 	[...]
> 	lib/test_kho.c:51:14: error: ‘KEXEC_KHO_FINALIZE’ undeclared (first use in this function)
> 	   51 |         case KEXEC_KHO_FINALIZE:
> 	      |              ^~~~~~~~~~~~~~~~~~
> 	[...]
>
> I think you need to update it as well to drop notifier usage.

Here's the fix. Build passes now and the test succeeds under my qemu
test setup.

--- 8< ---
>From a8e6b5dfef38bfbcd41f3dd08598cb79a0701d7e Mon Sep 17 00:00:00 2001
From: Pratyush Yadav <pratyush@xxxxxxxxxx>
Date: Mon, 6 Oct 2025 18:35:20 +0200
Subject: [PATCH] fixup! kho: drop notifiers

Update KHO test to drop the notifiers as well.

Signed-off-by: Pratyush Yadav <pratyush@xxxxxxxxxx>
---
 lib/test_kho.c | 32 +++-----------------------------
 1 file changed, 3 insertions(+), 29 deletions(-)

diff --git a/lib/test_kho.c b/lib/test_kho.c
index fe8504e3407b5..e9462a1e4b93b 100644
--- a/lib/test_kho.c
+++ b/lib/test_kho.c
@@ -38,33 +38,6 @@ 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;
@@ -111,6 +84,7 @@ 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);
 
@@ -194,7 +168,7 @@ static int kho_test_save(void)
 	if (err)
 		goto err_free_folios;
 
-	err = register_kho_notifier(&kho_test_nb);
+	err = kho_add_subtree(KHO_TEST_FDT, folio_address(state->fdt));
 	if (err)
 		goto err_free_fdt;
 
@@ -309,7 +283,7 @@ 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);
-- 
Regards,
Pratyush Yadav