6 files changed, 27 insertions, 3 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;
 }
 
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index fd78c84821c8..d35a3ca15fb5 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4315,7 +4315,7 @@ static void __free_extent_buffer(struct extent_buffer *eb)
         kmem_cache_free(extent_buffer_cache, eb);
 }
 
-static int extent_buffer_under_io(struct extent_buffer *eb)
+int extent_buffer_under_io(struct extent_buffer *eb)
 {
         return (atomic_read(&eb->io_pages) ||
                 test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 58b27e5ab521..c488b45237bf 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -320,6 +320,7 @@ int set_extent_buffer_dirty(struct extent_buffer *eb);
 int set_extent_buffer_uptodate(struct extent_buffer *eb);
 int clear_extent_buffer_uptodate(struct extent_buffer *eb);
 int extent_buffer_uptodate(struct extent_buffer *eb);
+int extent_buffer_under_io(struct extent_buffer *eb);
 int map_private_extent_buffer(struct extent_buffer *eb, unsigned long offset,
                       unsigned long min_len, char **map,
                       unsigned long *map_start,
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 9b6da9d55f9a..d00534b78382 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -5718,7 +5718,9 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
                         NULL);
         sort_clone_roots = 1;
 
+        current->journal_info = (void *)BTRFS_SEND_TRANS_STUB;
         ret = send_subvol(sctx);
+        current->journal_info = NULL;
         if (ret < 0)
                 goto out;
 
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index a04707f740d6..038177cfabbb 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -375,7 +375,8 @@ start_transaction(struct btrfs_root *root, u64 num_items, unsigned int type,
         if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))
                 return ERR_PTR(-EROFS);
 
-        if (current->journal_info) {
+        if (current->journal_info &&
+            current->journal_info != (void *)BTRFS_SEND_TRANS_STUB) {
                 WARN_ON(type & TRANS_EXTWRITERS);
                 h = current->journal_info;
                 h->use_count++;
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 6ac037e9f9f0..2bcba89d952e 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -78,6 +78,8 @@ struct btrfs_transaction {
 #define TRANS_EXTWRITERS        (__TRANS_USERSPACE | __TRANS_START |    \
                                  __TRANS_ATTACH)
 
+#define BTRFS_SEND_TRANS_STUB   1
+
 struct btrfs_trans_handle {
         u64 transid;
         u64 bytes_reserved;