Btrfs: add missing spin_lock for insertion into tree mod log

tree_mod_alloc calls __get_tree_mod_seq and must acquire a spinlock before
doing so.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 0954f17..26e8dc1 100644 (file)
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -455,11 +455,11 @@ unlock:
        return ret;
 }
 
-int tree_mod_alloc(struct btrfs_fs_info *fs_info, gfp_t flags,
-                  struct tree_mod_elem **tm_ret)
+static inline int tree_mod_alloc(struct btrfs_fs_info *fs_info, gfp_t flags,
+                                struct tree_mod_elem **tm_ret)
 {
        struct tree_mod_elem *tm;
-       u64 seq = 0;
+       int seq;
 
        smp_mb();
        if (list_empty(&fs_info->tree_mod_seq_list))
@@ -469,9 +469,22 @@ int tree_mod_alloc(struct btrfs_fs_info *fs_info, gfp_t flags,
        if (!tm)
                return -ENOMEM;
 
-       __get_tree_mod_seq(fs_info, &tm->elem);
-       seq = tm->elem.seq;
        tm->elem.flags = 0;
+       spin_lock(&fs_info->tree_mod_seq_lock);
+       if (list_empty(&fs_info->tree_mod_seq_list)) {
+               /*
+                * someone emptied the list while we were waiting for the lock.
+                * we must not add to the list, because no blocker exists. items
+                * are removed from the list only when the existing blocker is
+                * removed from the list.
+                */
+               kfree(tm);
+               seq = 0;
+       } else {
+               __get_tree_mod_seq(fs_info, &tm->elem);
+               seq = tm->elem.seq;
+       }
+       spin_unlock(&fs_info->tree_mod_seq_lock);
 
        return seq;
 }