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Diffstat (limited to 'fs/btrfs/relocation.c')
-rw-r--r--fs/btrfs/relocation.c51
1 files changed, 46 insertions, 5 deletions
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index c58245797f30..da5abd62db22 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -517,6 +517,34 @@ static int update_backref_cache(struct btrfs_trans_handle *trans,
return 1;
}
+static bool reloc_root_is_dead(struct btrfs_root *root)
+{
+ /*
+ * Pair with set_bit/clear_bit in clean_dirty_subvols and
+ * btrfs_update_reloc_root. We need to see the updated bit before
+ * trying to access reloc_root
+ */
+ smp_rmb();
+ if (test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state))
+ return true;
+ return false;
+}
+
+/*
+ * Check if this subvolume tree has valid reloc tree.
+ *
+ * Reloc tree after swap is considered dead, thus not considered as valid.
+ * This is enough for most callers, as they don't distinguish dead reloc root
+ * from no reloc root. But should_ignore_root() below is a special case.
+ */
+static bool have_reloc_root(struct btrfs_root *root)
+{
+ if (reloc_root_is_dead(root))
+ return false;
+ if (!root->reloc_root)
+ return false;
+ return true;
+}
static int should_ignore_root(struct btrfs_root *root)
{
@@ -525,6 +553,10 @@ static int should_ignore_root(struct btrfs_root *root)
if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
return 0;
+ /* This root has been merged with its reloc tree, we can ignore it */
+ if (reloc_root_is_dead(root))
+ return 1;
+
reloc_root = root->reloc_root;
if (!reloc_root)
return 0;
@@ -1439,7 +1471,7 @@ int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
* The subvolume has reloc tree but the swap is finished, no need to
* create/update the dead reloc tree
*/
- if (test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state))
+ if (reloc_root_is_dead(root))
return 0;
if (root->reloc_root) {
@@ -1478,8 +1510,7 @@ int btrfs_update_reloc_root(struct btrfs_trans_handle *trans,
struct btrfs_root_item *root_item;
int ret;
- if (test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state) ||
- !root->reloc_root)
+ if (!have_reloc_root(root))
goto out;
reloc_root = root->reloc_root;
@@ -1489,6 +1520,11 @@ int btrfs_update_reloc_root(struct btrfs_trans_handle *trans,
if (fs_info->reloc_ctl->merge_reloc_tree &&
btrfs_root_refs(root_item) == 0) {
set_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
+ /*
+ * Mark the tree as dead before we change reloc_root so
+ * have_reloc_root will not touch it from now on.
+ */
+ smp_wmb();
__del_reloc_root(reloc_root);
}
@@ -2201,6 +2237,11 @@ static int clean_dirty_subvols(struct reloc_control *rc)
if (ret2 < 0 && !ret)
ret = ret2;
}
+ /*
+ * Need barrier to ensure clear_bit() only happens after
+ * root->reloc_root = NULL. Pairs with have_reloc_root.
+ */
+ smp_wmb();
clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
btrfs_put_fs_root(root);
} else {
@@ -4718,7 +4759,7 @@ void btrfs_reloc_pre_snapshot(struct btrfs_pending_snapshot *pending,
struct btrfs_root *root = pending->root;
struct reloc_control *rc = root->fs_info->reloc_ctl;
- if (!root->reloc_root || !rc)
+ if (!rc || !have_reloc_root(root))
return;
if (!rc->merge_reloc_tree)
@@ -4752,7 +4793,7 @@ int btrfs_reloc_post_snapshot(struct btrfs_trans_handle *trans,
struct reloc_control *rc = root->fs_info->reloc_ctl;
int ret;
- if (!root->reloc_root || !rc)
+ if (!rc || !have_reloc_root(root))
return 0;
rc = root->fs_info->reloc_ctl;