1 files changed, 27 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6cb82f62cb7c..7c538f65214b 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -508,6 +508,33 @@ static noinline int device_list_add(const char *path,
                 ret = 1;
                 device->fs_devices = fs_devices;
         } else if (!device->name || strcmp(device->name->str, path)) {
+                /*
+                 * When FS is already mounted.
+                 * 1. If you are here and if the device->name is NULL that
+                 *    means this device was missing at time of FS mount.
+                 * 2. If you are here and if the device->name is different
+                 *    from 'path' that means either
+                 *      a. The same device disappeared and reappeared with
+                 *         different name. or
+                 *      b. The missing-disk-which-was-replaced, has
+                 *         reappeared now.
+                 *
+                 * We must allow 1 and 2a above. But 2b would be a spurious
+                 * and unintentional.
+                 *
+                 * Further in case of 1 and 2a above, the disk at 'path'
+                 * would have missed some transaction when it was away and
+                 * in case of 2a the stale bdev has to be updated as well.
+                 * 2b must not be allowed at all time.
+                 */
+
+                /*
+                 * As of now don't allow update to btrfs_fs_device through
+                 * the btrfs dev scan cli, after FS has been mounted.
+                 */
+                if (fs_devices->opened)
+                        return -EBUSY;
+
                 name = rcu_string_strdup(path, GFP_NOFS);
                 if (!name)
                         return -ENOMEM;