csdlock_debug uses early_param and static_branch_enable() to enable
csd_lock_wait feature, which triggers a panic on arm64 with config:
CONFIG_SPARSEMEM=y
CONFIG_SPARSEMEM_VMEMMAP=n

With CONFIG_SPARSEMEM_VMEMMAP=n, __nr_to_section is called in
static_key_enable() and returns NULL which makes NULL dereference
because mem_section is initialized in sparse_init() which is later
than parse_early_param() stage.

For powerpc this is also broken, because early_param stage is
earlier than jump_label_init() so static_key_enable won't work.
powerpc throws an warning: "static key 'xxx' used before call
to jump_label_init()".

Thus, early_param is too early for csd_lock_wait to run
static_branch_enable(), so changes it to __setup to fix these.

Fixes: 8d0968cc6b8f ("locking/csd_lock: Add boot parameter for controlling CSD lock debugging")
Cc: stable@vger.kernel.org
Reported-by: Chen jingwen <redacted>
Signed-off-by: Chen Zhongjin <redacted>
---
Change v3 -> v4:
Fix title and description because this fix is also applied
to powerpc.
For more detailed arm64 bug report see:
https://lore.kernel.org/linux-arm-kernel/e8715911-f835-059d-27f8-cc5f5ad30a07@huawei.com/t/ (local)

Change v2 -> v3:
Add module name in title

Change v1 -> v2:
Fix return 1 for __setup
---
 kernel/smp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index 65a630f62363..381eb15cd28f 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c

@@ -174,9 +174,9 @@ static int __init csdlock_debug(char *str)
 	if (val)
 		static_branch_enable(&csdlock_debug_enabled);
 
-	return 0;
+	return 1;
 }
-early_param("csdlock_debug", csdlock_debug);
+__setup("csdlock_debug=", csdlock_debug);
 
 static DEFINE_PER_CPU(call_single_data_t *, cur_csd);
 static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);