Btrfs: fix regression in scrub path resolving

In commit 4692cf58 we introduced new backref walking code for btrfs. This
assumes we're searching live roots, which requires a transaction context.
While scrubbing, however, we must not join a transaction because this could
deadlock with the commit path. Additionally, what scrub really wants to do
is resolving a logical address in the commit root it's currently checking.

This patch adds support for logical to path resolving on commit roots and
makes scrub use that.

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

4 files changed, 73 insertions, 55 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 0436c12da8c2..56136d9046f0 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -116,6 +116,7 @@ add_parent:
  * to a logical address
  */
 static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
+                                        int search_commit_root,
                                         struct __prelim_ref *ref,
                                         struct ulist *parents)
 {
@@ -131,6 +132,7 @@ static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
         path = btrfs_alloc_path();
         if (!path)
                 return -ENOMEM;
+        path->search_commit_root = !!search_commit_root;
 
         root_key.objectid = ref->root_id;
         root_key.type = BTRFS_ROOT_ITEM_KEY;
@@ -188,6 +190,7 @@ out:
  * resolve all indirect backrefs from the list
  */
 static int __resolve_indirect_refs(struct btrfs_fs_info *fs_info,
+                                   int search_commit_root,
                                    struct list_head *head)
 {
         int err;
@@ -212,7 +215,8 @@ static int __resolve_indirect_refs(struct btrfs_fs_info *fs_info,
                         continue;
                 if (ref->count == 0)
                         continue;
-                err = __resolve_indirect_ref(fs_info, ref, parents);
+                err = __resolve_indirect_ref(fs_info, search_commit_root,
+                                             ref, parents);
                 if (err) {
                         if (ret == 0)
                                 ret = err;
@@ -586,6 +590,7 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
         struct btrfs_delayed_ref_head *head;
         int info_level = 0;
         int ret;
+        int search_commit_root = (trans == BTRFS_BACKREF_SEARCH_COMMIT_ROOT);
         struct list_head prefs_delayed;
         struct list_head prefs;
         struct __prelim_ref *ref;
@@ -600,6 +605,7 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
         path = btrfs_alloc_path();
         if (!path)
                 return -ENOMEM;
+        path->search_commit_root = !!search_commit_root;
 
         /*
          * grab both a lock on the path and a lock on the delayed ref head.
@@ -614,35 +620,39 @@ again:
                 goto out;
         BUG_ON(ret == 0);
 
-        /*
-         * look if there are updates for this ref queued and lock the head
-         */
-        delayed_refs = &trans->transaction->delayed_refs;
-        spin_lock(&delayed_refs->lock);
-        head = btrfs_find_delayed_ref_head(trans, bytenr);
-        if (head) {
-                if (!mutex_trylock(&head->mutex)) {
-                        atomic_inc(&head->node.refs);
-                        spin_unlock(&delayed_refs->lock);
-
-                        btrfs_release_path(path);
-
-                        /*
-                         * Mutex was contended, block until it's
-                         * released and try again
-                         */
-                        mutex_lock(&head->mutex);
-                        mutex_unlock(&head->mutex);
-                        btrfs_put_delayed_ref(&head->node);
-                        goto again;
-                }
-                ret = __add_delayed_refs(head, seq, &info_key, &prefs_delayed);
-                if (ret) {
-                        spin_unlock(&delayed_refs->lock);
-                        goto out;
+        if (trans != BTRFS_BACKREF_SEARCH_COMMIT_ROOT) {
+                /*
+                 * look if there are updates for this ref queued and lock the
+                 * head
+                 */
+                delayed_refs = &trans->transaction->delayed_refs;
+                spin_lock(&delayed_refs->lock);
+                head = btrfs_find_delayed_ref_head(trans, bytenr);
+                if (head) {
+                        if (!mutex_trylock(&head->mutex)) {
+                                atomic_inc(&head->node.refs);
+                                spin_unlock(&delayed_refs->lock);
+
+                                btrfs_release_path(path);
+
+                                /*
+                                 * Mutex was contended, block until it's
+                                 * released and try again
+                                 */
+                                mutex_lock(&head->mutex);
+                                mutex_unlock(&head->mutex);
+                                btrfs_put_delayed_ref(&head->node);
+                                goto again;
+                        }
+                        ret = __add_delayed_refs(head, seq, &info_key,
+                                                 &prefs_delayed);
+                        if (ret) {
+                                spin_unlock(&delayed_refs->lock);
+                                goto out;
+                        }
                 }
+                spin_unlock(&delayed_refs->lock);
         }
-        spin_unlock(&delayed_refs->lock);
 
         if (path->slots[0]) {
                 struct extent_buffer *leaf;
@@ -679,7 +689,7 @@ again:
         if (ret)
                 goto out;
 
-        ret = __resolve_indirect_refs(fs_info, &prefs);
+        ret = __resolve_indirect_refs(fs_info, search_commit_root, &prefs);
         if (ret)
                 goto out;
 
@@ -1074,8 +1084,7 @@ int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
         return 0;
 }
 
-static int iterate_leaf_refs(struct btrfs_fs_info *fs_info,
-                                struct btrfs_path *path, u64 logical,
+static int iterate_leaf_refs(struct btrfs_fs_info *fs_info, u64 logical,
                                 u64 orig_extent_item_objectid,
                                 u64 extent_item_pos, u64 root,
                                 iterate_extent_inodes_t *iterate, void *ctx)
@@ -1143,35 +1152,38 @@ static int iterate_leaf_refs(struct btrfs_fs_info *fs_info,
  * calls iterate() for every inode that references the extent identified by
  * the given parameters.
  * when the iterator function returns a non-zero value, iteration stops.
- * path is guaranteed to be in released state when iterate() is called.
  */
 int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
-                                struct btrfs_path *path,
                                 u64 extent_item_objectid, u64 extent_item_pos,
+                                int search_commit_root,
                                 iterate_extent_inodes_t *iterate, void *ctx)
 {
         int ret;
         struct list_head data_refs = LIST_HEAD_INIT(data_refs);
         struct list_head shared_refs = LIST_HEAD_INIT(shared_refs);
         struct btrfs_trans_handle *trans;
-        struct ulist *refs;
-        struct ulist *roots;
+        struct ulist *refs = NULL;
+        struct ulist *roots = NULL;
         struct ulist_node *ref_node = NULL;
         struct ulist_node *root_node = NULL;
         struct seq_list seq_elem;
-        struct btrfs_delayed_ref_root *delayed_refs;
-
-        trans = btrfs_join_transaction(fs_info->extent_root);
-        if (IS_ERR(trans))
-                return PTR_ERR(trans);
+        struct btrfs_delayed_ref_root *delayed_refs = NULL;
 
         pr_debug("resolving all inodes for extent %llu\n",
                         extent_item_objectid);
 
-        delayed_refs = &trans->transaction->delayed_refs;
-        spin_lock(&delayed_refs->lock);
-        btrfs_get_delayed_seq(delayed_refs, &seq_elem);
-        spin_unlock(&delayed_refs->lock);
+        if (search_commit_root) {
+                trans = BTRFS_BACKREF_SEARCH_COMMIT_ROOT;
+        } else {
+                trans = btrfs_join_transaction(fs_info->extent_root);
+                if (IS_ERR(trans))
+                        return PTR_ERR(trans);
+
+                delayed_refs = &trans->transaction->delayed_refs;
+                spin_lock(&delayed_refs->lock);
+                btrfs_get_delayed_seq(delayed_refs, &seq_elem);
+                spin_unlock(&delayed_refs->lock);
+        }
 
         ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid,
                                    extent_item_pos, seq_elem.seq,
@@ -1188,7 +1200,7 @@ int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
                 while (!ret && (root_node = ulist_next(roots, root_node))) {
                         pr_debug("root %llu references leaf %llu\n",
                                         root_node->val, ref_node->val);
-                        ret = iterate_leaf_refs(fs_info, path, ref_node->val,
+                        ret = iterate_leaf_refs(fs_info, ref_node->val,
                                                 extent_item_objectid,
                                                 extent_item_pos, root_node->val,
                                                 iterate, ctx);
@@ -1198,8 +1210,11 @@ int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
         ulist_free(refs);
         ulist_free(roots);
 out:
-        btrfs_put_delayed_seq(delayed_refs, &seq_elem);
-        btrfs_end_transaction(trans, fs_info->extent_root);
+        if (!search_commit_root) {
+                btrfs_put_delayed_seq(delayed_refs, &seq_elem);
+                btrfs_end_transaction(trans, fs_info->extent_root);
+        }
+
         return ret;
 }
 
@@ -1210,6 +1225,7 @@ int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
         int ret;
         u64 extent_item_pos;
         struct btrfs_key found_key;
+        int search_commit_root = path->search_commit_root;
 
         ret = extent_from_logical(fs_info, logical, path,
                                         &found_key);
@@ -1220,8 +1236,9 @@ int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
                 return ret;
 
         extent_item_pos = logical - found_key.objectid;
-        ret = iterate_extent_inodes(fs_info, path, found_key.objectid,
-                                        extent_item_pos, iterate, ctx);
+        ret = iterate_extent_inodes(fs_info, found_key.objectid,
+                                        extent_item_pos, search_commit_root,
+                                        iterate, ctx);
 
         return ret;
 }
diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h
index d00dfa9ca934..57ea2e959e4d 100644
--- a/fs/btrfs/backref.h
+++ b/fs/btrfs/backref.h
@@ -22,6 +22,8 @@
 #include "ioctl.h"
 #include "ulist.h"
 
+#define BTRFS_BACKREF_SEARCH_COMMIT_ROOT ((struct btrfs_trans_handle *)0)
+
 struct inode_fs_paths {
         struct btrfs_path               *btrfs_path;
         struct btrfs_root               *fs_root;
@@ -44,9 +46,8 @@ int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
                                 u64 *out_root, u8 *out_level);
 
 int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
-                                struct btrfs_path *path,
                                 u64 extent_item_objectid,
-                                u64 extent_offset,
+                                u64 extent_offset, int search_commit_root,
                                 iterate_extent_inodes_t *iterate, void *ctx);
 
 int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 05446f77f99b..013c6371e3e8 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3067,8 +3067,8 @@ static long btrfs_ioctl_logical_to_ino(struct btrfs_root *root,
                 goto out;
 
         extent_item_pos = loi->logical - key.objectid;
-        ret = iterate_extent_inodes(root->fs_info, path, key.objectid,
-                                        extent_item_pos, build_ino_list,
+        ret = iterate_extent_inodes(root->fs_info, key.objectid,
+                                        extent_item_pos, 0, build_ino_list,
                                         inodes);
 
         if (ret < 0)
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index abc0fbffa510..b9b84cdfc359 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -352,8 +352,8 @@ static void scrub_print_warning(const char *errstr, struct scrub_bio *sbio,
                 } while (ret != 1);
         } else {
                 swarn.path = path;
-                iterate_extent_inodes(fs_info, path, found_key.objectid,
-                                        extent_item_pos,
+                iterate_extent_inodes(fs_info, found_key.objectid,
+                                        extent_item_pos, 1,
                                         scrub_print_warning_inode, &swarn);
         }