Btrfs: assert send doesn't attempt to start transactions

When starting a transaction just assert that current->journal_info
doesn't contain a send transaction stub, since send isn't supposed
to start transactions and when it finishes (either successfully or
not) it's supposed to set current->journal_info to NULL.

This is motivated by the change titled:

    Btrfs: fix crash when starting transaction

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 511839c04f11..a32ad65b6cdc 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -386,11 +386,13 @@ start_transaction(struct btrfs_root *root, u64 num_items, unsigned int type,
         bool reloc_reserved = false;
         int ret;
 
+        /* Send isn't supposed to start transactions. */
+        ASSERT(current->journal_info != (void *)BTRFS_SEND_TRANS_STUB);
+
         if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))
                 return ERR_PTR(-EROFS);
 
-        if (current->journal_info &&
-            current->journal_info != (void *)BTRFS_SEND_TRANS_STUB) {
+        if (current->journal_info) {
                 WARN_ON(type & TRANS_EXTWRITERS);
                 h = current->journal_info;
                 h->use_count++;