powerpc/code-patching: Use WARN_ON and fix check in poking_init

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 <bgray@linux.ibm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221109045112.187069-3-bgray@linux.ibm.com

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index ad0cf3108dd09c78c5fb50d1395253ef5d43d6f6..3055eef7dcdcc80779f96043da768ca0ad1bd74d 100644 (file)
--- 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);
 }