bcachefs: bch_dev->dev

Add a field to bch_dev for the dev_t of the underlying block device -
this fixes a null ptr deref in tracepoints.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/bcachefs.h

@@ -432,6 +432,7 @@ struct bch_dev {
 	struct bch_sb_handle	disk_sb;
 	struct bch_sb		*sb_read_scratch;
 	int			sb_write_error;
+	dev_t			dev;
 
 	struct bch_devs_mask	self;
 

fs/bcachefs/chardev.c

@@ -568,8 +568,11 @@ static long bch2_ioctl_disk_get_idx(struct bch_fs *c,
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
+	if (!dev)
+		return -EINVAL;
+
 	for_each_online_member(ca, c, i)
-		if (ca->disk_sb.bdev->bd_dev == dev) {
+		if (ca->dev == dev) {
 			percpu_ref_put(&ca->io_ref);
 			return i;
 		}

fs/bcachefs/super.c

@@ -1257,6 +1257,8 @@ static int __bch2_dev_attach_bdev(struct bch_dev *ca, struct bch_sb_handle *sb)
 	ca->disk_sb = *sb;
 	memset(sb, 0, sizeof(*sb));
 
+	ca->dev = ca->disk_sb.bdev->bd_dev;
+
 	percpu_ref_reinit(&ca->io_ref);
 
 	return 0;
@@ -1875,7 +1877,7 @@ struct bch_dev *bch2_dev_lookup(struct bch_fs *c, const char *path)
 
 	rcu_read_lock();
 	for_each_member_device_rcu(ca, c, i, NULL)
-		if (ca->disk_sb.bdev->bd_dev == dev)
+		if (ca->dev == dev)
 			goto found;
 	ca = ERR_PTR(-ENOENT);
 found:

fs/bcachefs/trace.h

@@ -387,7 +387,7 @@ TRACE_EVENT(alloc_scan,
 	),
 
 	TP_fast_assign(
-		__entry->dev		= ca->disk_sb.bdev->bd_dev;
+		__entry->dev		= ca->dev;
 		__entry->found		= found;
 		__entry->inc_gen	= inc_gen;
 		__entry->inc_gen_skipped = inc_gen_skipped;
@@ -409,7 +409,7 @@ TRACE_EVENT(invalidate,
 	),
 
 	TP_fast_assign(
-		__entry->dev		= ca->disk_sb.bdev->bd_dev;
+		__entry->dev		= ca->dev;
 		__entry->offset		= offset,
 		__entry->sectors	= sectors;
 	),
@@ -431,7 +431,7 @@ DECLARE_EVENT_CLASS(bucket_alloc,
 	),
 
 	TP_fast_assign(
-		__entry->dev		= ca->disk_sb.bdev->bd_dev;
+		__entry->dev		= ca->dev;
 		__entry->reserve	= reserve;
 	),