btrfs-progs: Fix bug when scanned for devid which was missing and deleted

get_fs_info() provides the info of the specific
device/devid, however when we delete the missing disk
the super-block on the disk isn't cleared, and since
btrfs-progs makes its decision by reading the disk super
block, so it doesn't know about the kernel previous action,
And now when we tried to probe kernel for the devid it fails.

reproducer:

$ mkfs.btrfs -d raid1 -m raid1 /dev/sde /dev/sdf
$ modprobe -r btrfs && modprobe btrfs
$ mount -o degraded /dev/sde /btrfs
$ btrfs dev add /dev/sdd /btrfs
$ btrfs dev del missing /btrfs
$ btrfs scrub start -B /dev/sdf
btrfs: utils.c:1741: get_fs_info: Assertion `!(ndevs == 0)' failed.
Aborted (core dumped)

Signed-off-by: Anand Jain <Anand.Jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/utils.c b/utils.c
index ef7fb463..78e4ba1c 100644
--- a/utils.c
+++ b/utils.c
@@ -1752,8 +1752,15 @@ int get_fs_info(char *path, struct btrfs_ioctl_fs_info_args *fi_args,
 		ndevs++;
 	}
 
-	BUG_ON(ndevs == 0);
-	ret = 0;
+	/*
+	* only when the only dev we wanted to find is not there then
+	* let any error be returned
+	*/
+	if (fi_args->num_devices != 1) {
+		BUG_ON(ndevs == 0);
+		ret = 0;
+	}
+
 out:
 	close_file_or_dir(fd, dirstream);
 	return ret;