[PATCH] jump_label: Fix usage in module __init

[Peter Zijlstra]

Final patch looks like this.

---
Subject: jump_label: Fix usage in module __init
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed Dec 16 12:21:36 CET 2020

When the static_key is part of the module, and the module calls
static_key_inc/enable() from it's __init section *AND* has a
static_branch_*() user in that very same __init section, things go
wobbly.

If the static_key lives outside the module, jump_label_add_module()
would append this module's sites to the key and jump_label_update()
would take the static_key_linked() branch and all would be fine.

If all the sites are outside of __init, then everything will be fine
too.

However, when all is aligned just as described above,
jump_label_update() calls __jump_label_update(.init = false) and we'll
not update sites in __init text.

Fixes: 19483677684b ("jump_label: Annotate entries that operate on __init code earlier")
Reported-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Jessica Yu <jeyu@xxxxxxxxxx>
---
 kernel/jump_label.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -793,6 +793,7 @@ int jump_label_text_reserved(void *start
 static void jump_label_update(struct static_key *key)
 {
 	struct jump_entry *stop = __stop___jump_table;
+	bool init = system_state < SYSTEM_RUNNING;
 	struct jump_entry *entry;
 #ifdef CONFIG_MODULES
 	struct module *mod;
@@ -804,15 +805,16 @@ static void jump_label_update(struct sta
 
 	preempt_disable();
 	mod = __module_address((unsigned long)key);
-	if (mod)
+	if (mod) {
 		stop = mod->jump_entries + mod->num_jump_entries;
+		init = mod->state == MODULE_STATE_COMING;
+	}
 	preempt_enable();
 #endif
 	entry = static_key_entries(key);
 	/* if there are no users, entry can be NULL */
 	if (entry)
-		__jump_label_update(key, entry, stop,
-				    system_state < SYSTEM_RUNNING);
+		__jump_label_update(key, entry, stop, init);
 }
 
 #ifdef CONFIG_STATIC_KEYS_SELFTEST