Btrfs: hold the tree mod lock in __tree_mod_log_rewind

We need to hold the tree mod log lock in __tree_mod_log_rewind since we walk
forward in the tree mod entries, otherwise we'll end up with random entries and
trip the BUG_ON() at the front of __tree_mod_log_rewind.  This fixes the panics
people were seeing when running

find /whatever -type f -exec btrfs fi defrag {} \;

Thansk,

Cc: stable@vger.kernel.org
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index c32d03dff4fc..7921e1d9d59c 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1161,8 +1161,8 @@ __tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info,
  * time_seq).
  */
 static void
-__tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq,
-                      struct tree_mod_elem *first_tm)
+__tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
+                      u64 time_seq, struct tree_mod_elem *first_tm)
 {
         u32 n;
         struct rb_node *next;
@@ -1172,6 +1172,7 @@ __tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq,
         unsigned long p_size = sizeof(struct btrfs_key_ptr);
 
         n = btrfs_header_nritems(eb);
+        tree_mod_log_read_lock(fs_info);
         while (tm && tm->seq >= time_seq) {
                 /*
                  * all the operations are recorded with the operator used for
@@ -1226,6 +1227,7 @@ __tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq,
                 if (tm->index != first_tm->index)
                         break;
         }
+        tree_mod_log_read_unlock(fs_info);
         btrfs_set_header_nritems(eb, n);
 }
 
@@ -1274,7 +1276,7 @@ tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
 
         extent_buffer_get(eb_rewin);
         btrfs_tree_read_lock(eb_rewin);
-        __tree_mod_log_rewind(eb_rewin, time_seq, tm);
+        __tree_mod_log_rewind(fs_info, eb_rewin, time_seq, tm);
         WARN_ON(btrfs_header_nritems(eb_rewin) >
                 BTRFS_NODEPTRS_PER_BLOCK(fs_info->tree_root));
 
@@ -1350,7 +1352,7 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
                 btrfs_set_header_generation(eb, old_generation);
         }
         if (tm)
-                __tree_mod_log_rewind(eb, time_seq, tm);
+                __tree_mod_log_rewind(root->fs_info, eb, time_seq, tm);
         else
                 WARN_ON(btrfs_header_level(eb) != 0);
         WARN_ON(btrfs_header_nritems(eb) > BTRFS_NODEPTRS_PER_BLOCK(root));