bcachefs: six locks: write locks can now be held recursively

This is needed for the interior update locking rework, where we'll be
holding node write locks for the duration of the update - which is
needed for synchronizing with online check_allocations.

Signed-off-by: Kent Overstreet <[email protected]>

Author: Kent Overstreet

fs/bcachefs/six.c

@@ -616,15 +616,22 @@ void six_unlock_ip(struct six_lock *lock, enum six_lock_type type, unsigned long
 
 	if (type != SIX_LOCK_write)
 		six_release(&lock->dep_map, ip);
-	else
-		lock->seq++;
 
 	if (type == SIX_LOCK_intent &&
 	    lock->intent_lock_recurse) {
 		--lock->intent_lock_recurse;
 		return;
 	}
 
+	if (type == SIX_LOCK_write &&
+	    lock->write_lock_recurse) {
+		--lock->write_lock_recurse;
+		return;
+	}
+
+	if (type == SIX_LOCK_write)
+		lock->seq++;
+
 	do_six_unlock_type(lock, type);
 }
 EXPORT_SYMBOL_GPL(six_unlock_ip);
@@ -735,13 +742,13 @@ void six_lock_increment(struct six_lock *lock, enum six_lock_type type)
 			atomic_add(l[type].lock_val, &lock->state);
 		}
 		break;
+	case SIX_LOCK_write:
+		lock->write_lock_recurse++;
+		fallthrough;
 	case SIX_LOCK_intent:
 		EBUG_ON(!(atomic_read(&lock->state) & SIX_LOCK_HELD_intent));
 		lock->intent_lock_recurse++;
 		break;
-	case SIX_LOCK_write:
-		BUG();
-		break;
 	}
 }
 EXPORT_SYMBOL_GPL(six_lock_increment);

fs/bcachefs/six.h

@@ -137,6 +137,7 @@ struct six_lock {
 	atomic_t		state;
 	u32			seq;
 	unsigned		intent_lock_recurse;
+	unsigned		write_lock_recurse;
 	struct task_struct	*owner;
 	unsigned __percpu	*readers;
 	raw_spinlock_t		wait_lock;