bcachefs: Fix device add

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_gc.c

@@ -327,9 +327,16 @@ void bch2_mark_dev_superblock(struct bch_fs *c, struct bch_dev *ca,
 	unsigned i;
 	u64 b;
 
+	/*
+	 * This conditional is kind of gross, but we may be called from the
+	 * device add path, before the new device has actually been added to the
+	 * running filesystem:
+	 */
 	if (c) {
 		lockdep_assert_held(&c->sb_lock);
 		percpu_down_read(&c->usage_lock);
+	} else {
+		preempt_disable();
 	}
 
 	for (i = 0; i < layout->nr_superblocks; i++) {
@@ -357,6 +364,8 @@ void bch2_mark_dev_superblock(struct bch_fs *c, struct bch_dev *ca,
 	if (c) {
 		spin_unlock(&c->journal.lock);
 		percpu_up_read(&c->usage_lock);
+	} else {
+		preempt_enable();
 	}
 }
 

fs/bcachefs/journal.c

@@ -727,6 +727,10 @@ static int __bch2_set_nr_journal_buckets(struct bch_dev *ca, unsigned nr,
 	if (!journal_buckets)
 		goto err;
 
+	/*
+	 * We may be called from the device add path, before the new device has
+	 * actually been added to the running filesystem:
+	 */
 	if (c)
 		spin_lock(&c->journal.lock);
 
@@ -743,10 +747,7 @@ static int __bch2_set_nr_journal_buckets(struct bch_dev *ca, unsigned nr,
 		long bucket;
 
 		if (new_fs) {
-			percpu_down_read(&c->usage_lock);
 			bucket = bch2_bucket_alloc_new_fs(ca);
-			percpu_up_read(&c->usage_lock);
-
 			if (bucket < 0) {
 				ret = -ENOSPC;
 				goto err;
@@ -765,6 +766,8 @@ static int __bch2_set_nr_journal_buckets(struct bch_dev *ca, unsigned nr,
 		if (c) {
 			percpu_down_read(&c->usage_lock);
 			spin_lock(&c->journal.lock);
+		} else {
+			preempt_disable();
 		}
 
 		__array_insert_item(ja->buckets,		ja->nr, ja->last_idx);
@@ -792,6 +795,8 @@ static int __bch2_set_nr_journal_buckets(struct bch_dev *ca, unsigned nr,
 		if (c) {
 			spin_unlock(&c->journal.lock);
 			percpu_up_read(&c->usage_lock);
+		} else {
+			preempt_enable();
 		}
 
 		if (!new_fs)