Subject: [PATCH v10 2/9] powerpc/code-patching: Use WARN_ON and fix check in poking_init

From: Benjamin Gray <[email-masked]>
Date: Wed, 9 Nov 2022 15:51:05 +1100

BUG_ON() when failing to initialise the code patching window is
unnecessary, and use of BUG_ON is discouraged. We don't set
poking_init_done in this case, so failure to init the boot CPU will
result in a strict RWX error when a following patch_instruction uses
raw_patch_instruction. If it only fails for later CPUs, they won't be
onlined in the first place.

The return value of cpuhp_setup_state() is also >= 0 on success,
so check for < 0.

Signed-off-by: Benjamin Gray <[email-masked]>
---
v10:	* Don't mention caller recovery
	* Don't set poking_init_done on failure
	* Add setup return code comment from later patch
	* Reviewed-by not applied because of above changes
v9:	* Reword commit message to explain why init failure is not fatal
---
 arch/powerpc/lib/code-patching.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index ad0cf3108dd0..3055eef7dcdc 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -81,16 +81,17 @@ static int text_area_cpu_down(unsigned int cpu)
 
 static __ro_after_init DEFINE_STATIC_KEY_FALSE(poking_init_done);
 
-/*
- * Although BUG_ON() is rude, in this case it should only happen if ENOMEM, and
- * we judge it as being preferable to a kernel that will crash later when
- * someone tries to use patch_instruction().
- */
 void __init poking_init(void)
 {
-	BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
-		"powerpc/text_poke:online", text_area_cpu_up,
-		text_area_cpu_down));
+	int ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
+				    "powerpc/text_poke:online",
+				    text_area_cpu_up,
+				    text_area_cpu_down);
+
+	/* cpuhp_setup_state returns >= 0 on success */
+	if (WARN_ON(ret < 0))
+		return;
+
 	static_branch_enable(&poking_init_done);
 }
 
-- 
2.38.1