[PATCH rcu 06/12] locking/csd_lock: Change csdlock_debug from early_param to __setup

[Paul E. McKenney]

From: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>

The csdlock_debug kernel-boot parameter is parsed by the
early_param() function csdlock_debug().  If set, csdlock_debug()
invokes static_branch_enable() to enable csd_lock_wait feature, which
triggers a panic on arm64 for kernels built with CONFIG_SPARSEMEM=y and
CONFIG_SPARSEMEM_VMEMMAP=n.

With CONFIG_SPARSEMEM_VMEMMAP=n, __nr_to_section is called in
static_key_enable() and returns NULL, resulting in a NULL dereference
because mem_section is initialized only later in sparse_init().

This is also a problem for powerpc because early_param() functions
are invoked earlier than jump_label_init(), also resulting in
static_key_enable() failures.  These failures cause the 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@xxxxxxxxxxxxxxx
Reported-by: Chen jingwen <chenjingwen6@xxxxxxxxxx>
Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/smp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index dd215f4394264..650810a6f29b3 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);
-- 
2.31.1.189.g2e36527f23