1 files changed, 19 insertions, 1 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d9698fda2d12..98fe70193397 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -329,6 +329,8 @@ static int verify_parent_transid(struct extent_io_tree *io_tree,
 {
         struct extent_state *cached_state = NULL;
         int ret;
+        bool need_lock = (current->journal_info ==
+                          (void *)BTRFS_SEND_TRANS_STUB);
 
         if (!parent_transid || btrfs_header_generation(eb) == parent_transid)
                 return 0;
@@ -336,6 +338,11 @@ static int verify_parent_transid(struct extent_io_tree *io_tree,
         if (atomic)
                 return -EAGAIN;
 
+        if (need_lock) {
+                btrfs_tree_read_lock(eb);
+                btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
+        }
+
         lock_extent_bits(io_tree, eb->start, eb->start + eb->len - 1,
                          0, &cached_state);
         if (extent_buffer_uptodate(eb) &&
@@ -347,10 +354,21 @@ static int verify_parent_transid(struct extent_io_tree *io_tree,
                        "found %llu\n",
                        eb->start, parent_transid, btrfs_header_generation(eb));
         ret = 1;
-        clear_extent_buffer_uptodate(eb);
+
+        /*
+         * Things reading via commit roots that don't have normal protection,
+         * like send, can have a really old block in cache that may point at a
+         * block that has been free'd and re-allocated.  So don't clear uptodate
+         * if we find an eb that is under IO (dirty/writeback) because we could
+         * end up reading in the stale data and then writing it back out and
+         * making everybody very sad.
+         */
+        if (!extent_buffer_under_io(eb))
+                clear_extent_buffer_uptodate(eb);
 out:
         unlock_extent_cached(io_tree, eb->start, eb->start + eb->len - 1,
                              &cached_state, GFP_NOFS);
+        btrfs_tree_read_unlock_blocking(eb);
         return ret;
 }