Btrfs: fix race between block group relocation and nocow writes

[mirror_ubuntu-bionic-kernel.git] / fs / btrfs / extent-tree.c

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 09aad7b447f5670efc5301dcdd197df8ce5a5648..dcf89bfa990da427a9b74805c87e4a88e51afdab 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3824,6 +3824,59 @@ int btrfs_extent_readonly(struct btrfs_root *root, u64 bytenr)
        return readonly;
 }
 
+bool btrfs_inc_nocow_writers(struct btrfs_fs_info *fs_info, u64 bytenr)
+{
+       struct btrfs_block_group_cache *bg;
+       bool ret = true;
+
+       bg = btrfs_lookup_block_group(fs_info, bytenr);
+       if (!bg)
+               return false;
+
+       spin_lock(&bg->lock);
+       if (bg->ro)
+               ret = false;
+       else
+               atomic_inc(&bg->nocow_writers);
+       spin_unlock(&bg->lock);
+
+       /* no put on block group, done by btrfs_dec_nocow_writers */
+       if (!ret)
+               btrfs_put_block_group(bg);
+
+       return ret;
+
+}
+
+void btrfs_dec_nocow_writers(struct btrfs_fs_info *fs_info, u64 bytenr)
+{
+       struct btrfs_block_group_cache *bg;
+
+       bg = btrfs_lookup_block_group(fs_info, bytenr);
+       ASSERT(bg);
+       if (atomic_dec_and_test(&bg->nocow_writers))
+               wake_up_atomic_t(&bg->nocow_writers);
+       /*
+        * Once for our lookup and once for the lookup done by a previous call
+        * to btrfs_inc_nocow_writers()
+        */
+       btrfs_put_block_group(bg);
+       btrfs_put_block_group(bg);
+}
+
+static int btrfs_wait_nocow_writers_atomic_t(atomic_t *a)
+{
+       schedule();
+       return 0;
+}
+
+void btrfs_wait_nocow_writers(struct btrfs_block_group_cache *bg)
+{
+       wait_on_atomic_t(&bg->nocow_writers,
+                        btrfs_wait_nocow_writers_atomic_t,
+                        TASK_UNINTERRUPTIBLE);
+}
+
 static const char *alloc_name(u64 flags)
 {
        switch (flags) {