Revert "jump_label: Prevent key->enabled int overflow"

This reverts commit 550cb99691 which is
commit eb8c507296 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ibfe863eab77b6e07e72bd50022cd994ee15d75dc
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

include/linux/jump_label.h

@@ -247,10 +247,9 @@ extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
 					    enum jump_label_type type);
 extern void arch_jump_label_transform_apply(void);
 extern int jump_label_text_reserved(void *start, void *end);
-extern bool static_key_slow_inc(struct static_key *key);
+extern void static_key_slow_inc(struct static_key *key);
-extern bool static_key_fast_inc_not_disabled(struct static_key *key);
 extern void static_key_slow_dec(struct static_key *key);
-extern bool static_key_slow_inc_cpuslocked(struct static_key *key);
+extern void static_key_slow_inc_cpuslocked(struct static_key *key);
 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
 extern int static_key_count(struct static_key *key);
 extern void static_key_enable(struct static_key *key);
@@ -302,23 +301,11 @@ static __always_inline bool static_key_true(struct static_key *key)
 	return false;
 }
 
-static inline bool static_key_fast_inc_not_disabled(struct static_key *key)
+static inline void static_key_slow_inc(struct static_key *key)
 {
-	int v;
-
 	STATIC_KEY_CHECK_USE(key);
-	/*
+	atomic_inc(&key->enabled);
-	 * Prevent key->enabled getting negative to follow the same semantics
-	 * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment.
-	 */
-	v = atomic_read(&key->enabled);
-	do {
-		if (v < 0 || (v + 1) < 0)
-			return false;
-	} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
-	return true;
 }
-#define static_key_slow_inc(key)	static_key_fast_inc_not_disabled(key)
 
 static inline void static_key_slow_dec(struct static_key *key)
 {

kernel/jump_label.c

@@ -113,40 +113,9 @@ int static_key_count(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_count);
 
-/*
+void static_key_slow_inc_cpuslocked(struct static_key *key)
- * static_key_fast_inc_not_disabled - adds a user for a static key
- * @key: static key that must be already enabled
- *
- * The caller must make sure that the static key can't get disabled while
- * in this function. It doesn't patch jump labels, only adds a user to
- * an already enabled static key.
- *
- * Returns true if the increment was done. Unlike refcount_t the ref counter
- * is not saturated, but will fail to increment on overflow.
- */
-bool static_key_fast_inc_not_disabled(struct static_key *key)
 {
-	int v;
-
 	STATIC_KEY_CHECK_USE(key);
-	/*
-	 * Negative key->enabled has a special meaning: it sends
-	 * static_key_slow_inc() down the slow path, and it is non-zero
-	 * so it counts as "enabled" in jump_label_update().  Note that
-	 * atomic_inc_unless_negative() checks >= 0, so roll our own.
-	 */
-	v = atomic_read(&key->enabled);
-	do {
-		if (v <= 0 || (v + 1) < 0)
-			return false;
-	} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
-
-	return true;
-}
-EXPORT_SYMBOL_GPL(static_key_fast_inc_not_disabled);
-
-bool static_key_slow_inc_cpuslocked(struct static_key *key)
-{
 	lockdep_assert_cpus_held();
 
 	/*
@@ -155,9 +124,15 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key)
 	 * jump_label_update() process.  At the same time, however,
 	 * the jump_label_update() call below wants to see
 	 * static_key_enabled(&key) for jumps to be updated properly.
+	 *
+	 * So give a special meaning to negative key->enabled: it sends
+	 * static_key_slow_inc() down the slow path, and it is non-zero
+	 * so it counts as "enabled" in jump_label_update().  Note that
+	 * atomic_inc_unless_negative() checks >= 0, so roll our own.
 	 */
-	if (static_key_fast_inc_not_disabled(key))
+	for (int v = atomic_read(&key->enabled); v > 0; )
-		return true;
+		if (likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)))
+			return;
 
 	jump_label_lock();
 	if (atomic_read(&key->enabled) == 0) {
@@ -169,23 +144,16 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key)
 		 */
 		atomic_set_release(&key->enabled, 1);
 	} else {
-		if (WARN_ON_ONCE(!static_key_fast_inc_not_disabled(key))) {
+		atomic_inc(&key->enabled);
-			jump_label_unlock();
-			return false;
-		}
 	}
 	jump_label_unlock();
-	return true;
 }
 
-bool static_key_slow_inc(struct static_key *key)
+void static_key_slow_inc(struct static_key *key)
 {
-	bool ret;
-
 	cpus_read_lock();
-	ret = static_key_slow_inc_cpuslocked(key);
+	static_key_slow_inc_cpuslocked(key);
 	cpus_read_unlock();
-	return ret;
 }
 EXPORT_SYMBOL_GPL(static_key_slow_inc);