btrfs: fix error handling in btrfs_dev_replace_start

When we fail to start a transaction in btrfs_dev_replace_start, we leave
dev_replace->replace_start set to STARTED but clear ->srcdev and
->tgtdev.  Later, that can result in an Oops in
btrfs_dev_replace_progress when having state set to STARTED or SUSPENDED
implies that ->srcdev is valid.

Also fix error handling when the state is already STARTED or SUSPENDED
while starting.  That, too, will clear ->srcdev and ->tgtdev even though
it doesn't own them.  This should be an impossible case to hit since we
should be protected by the BTRFS_FS_EXCL_OP bit being set.  Let's add an
ASSERT there while we're at it.

Fixes: e93c89c1aaaaa (Btrfs: add new sources for device replace code)
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 4e2b67d06305..ff01740158aa 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -440,6 +440,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
                 break;
         case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
         case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
+                ASSERT(0);
                 ret = BTRFS_IOCTL_DEV_REPLACE_RESULT_ALREADY_STARTED;
                 goto leave;
         }
@@ -482,6 +483,10 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
         if (IS_ERR(trans)) {
                 ret = PTR_ERR(trans);
                 btrfs_dev_replace_write_lock(dev_replace);
+                dev_replace->replace_state =
+                        BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED;
+                dev_replace->srcdev = NULL;
+                dev_replace->tgtdev = NULL;
                 goto leave;
         }
 
@@ -503,8 +508,6 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
         return ret;
 
 leave:
-        dev_replace->srcdev = NULL;
-        dev_replace->tgtdev = NULL;
         btrfs_dev_replace_write_unlock(dev_replace);
         btrfs_destroy_dev_replace_tgtdev(tgt_device);
         return ret;