six locks: Remove hacks for percpu mode lost wakeup

The lost wakeup bug hasn't been observed in awhile, and we're trying to
provoke it and determine if it still exists.

This patch removes some defenses that were added to attempt to track it
down; if it still exists, this should make it easier to see it.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/six.c

@@ -144,17 +144,8 @@ static int __do_six_trylock_type(struct six_lock *lock,
 		 * lock, issue a wakeup because we might have caused a
 		 * spurious trylock failure:
 		 */
-#if 0
-		/*
-		 * This code should be sufficient, but we're seeing unexplained
-		 * lost wakeups:
-		 */
 		if (old.write_locking)
 			ret = -1 - SIX_LOCK_write;
-#else
-		if (!ret)
-			ret = -1 - SIX_LOCK_write;
-#endif
 	} else if (type == SIX_LOCK_write && lock->readers) {
 		if (try) {
 			atomic64_add(__SIX_VAL(write_locking, 1),
@@ -332,7 +323,7 @@ static bool __six_relock_type(struct six_lock *lock, enum six_lock_type type,
 		 */
 		if (ret)
 			six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read, ip);
-		else
+		else if (old.write_locking)
 			six_lock_wakeup(lock, old, SIX_LOCK_write);
 
 		return ret;