static_call: Fix static_call_set_init()

It turns out that static_call_set_init() does not preserve the other
flags; IOW. it clears TAIL if it was set.

Fixes: 9183c3f9 ("static_call: Add inline static call infrastructure")
Reported-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Sumit Garg <sumit.garg@linaro.org>
Link: https://lkml.kernel.org/r/20210318113610.519406371@infradead.org

kernel/static_call.c

@@ -35,27 +35,30 @@ static inline void *static_call_addr(struct static_call_site *site)
 	return (void *)((long)site->addr + (long)&site->addr);
 }
 
+static inline unsigned long __static_call_key(const struct static_call_site *site)
+{
+	return (long)site->key + (long)&site->key;
+}
 
 static inline struct static_call_key *static_call_key(const struct static_call_site *site)
 {
-	return (struct static_call_key *)
-		(((long)site->key + (long)&site->key) & ~STATIC_CALL_SITE_FLAGS);
+	return (void *)(__static_call_key(site) & ~STATIC_CALL_SITE_FLAGS);
 }
 
 /* These assume the key is word-aligned. */
 static inline bool static_call_is_init(struct static_call_site *site)
 {
-	return ((long)site->key + (long)&site->key) & STATIC_CALL_SITE_INIT;
+	return __static_call_key(site) & STATIC_CALL_SITE_INIT;
 }
 
 static inline bool static_call_is_tail(struct static_call_site *site)
 {
-	return ((long)site->key + (long)&site->key) & STATIC_CALL_SITE_TAIL;
+	return __static_call_key(site) & STATIC_CALL_SITE_TAIL;
 }
 
 static inline void static_call_set_init(struct static_call_site *site)
 {
-	site->key = ((long)static_call_key(site) | STATIC_CALL_SITE_INIT) -
+	site->key = (__static_call_key(site) | STATIC_CALL_SITE_INIT) -
 		    (long)&site->key;
 }
 
@@ -349,7 +352,7 @@ static int static_call_add_module(struct module *mod)
 	struct static_call_site *site;
 
 	for (site = start; site != stop; site++) {
-		unsigned long s_key = (long)site->key + (long)&site->key;
+		unsigned long s_key = __static_call_key(site);
 		unsigned long addr = s_key & ~STATIC_CALL_SITE_FLAGS;
 		unsigned long key;