Btrfs: fix up read_tree_block to return proper error

The return value of read_tree_block() can confuse callers as it always
returns NULL for either -ENOMEM or -EIO, so it's likely that callers
parse it to a wrong error, for instance, in btrfs_read_tree_root().

This fixes the above issue.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

5 files changed, 54 insertions, 29 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 614aaa1969bd..679dc97354be 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -491,7 +491,9 @@ static int __add_missing_keys(struct btrfs_fs_info *fs_info,
                 BUG_ON(!ref->wanted_disk_byte);
                 eb = read_tree_block(fs_info->tree_root, ref->wanted_disk_byte,
                                      0);
-                if (!eb || !extent_buffer_uptodate(eb)) {
+                if (IS_ERR(eb)) {
+                        return PTR_ERR(eb);
+                } else if (!extent_buffer_uptodate(eb)) {
                         free_extent_buffer(eb);
                         return -EIO;
                 }
@@ -1034,7 +1036,10 @@ again:
 
                                 eb = read_tree_block(fs_info->extent_root,
                                                            ref->parent, 0);
-                                if (!eb || !extent_buffer_uptodate(eb)) {
+                                if (IS_ERR(eb)) {
+                                        ret = PTR_ERR(eb);
+                                        goto out;
+                                } else if (!extent_buffer_uptodate(eb)) {
                                         free_extent_buffer(eb);
                                         ret = -EIO;
                                         goto out;
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 0f11ebc92f02..54114b4887dd 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1439,8 +1439,9 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
                 btrfs_tree_read_unlock(eb_root);
                 free_extent_buffer(eb_root);
                 old = read_tree_block(root, logical, 0);
-                if (WARN_ON(!old || !extent_buffer_uptodate(old))) {
-                        free_extent_buffer(old);
+                if (WARN_ON(IS_ERR(old) || !extent_buffer_uptodate(old))) {
+                        if (!IS_ERR(old))
+                                free_extent_buffer(old);
                         btrfs_warn(root->fs_info,
                                 "failed to read tree block %llu from get_old_root", logical);
                 } else {
@@ -1685,7 +1686,9 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
                 if (!cur || !uptodate) {
                         if (!cur) {
                                 cur = read_tree_block(root, blocknr, gen);
-                                if (!cur || !extent_buffer_uptodate(cur)) {
+                                if (IS_ERR(cur)) {
+                                        return PTR_ERR(cur);
+                                } else if (!extent_buffer_uptodate(cur)) {
                                         free_extent_buffer(cur);
                                         return -EIO;
                                 }
@@ -1864,8 +1867,9 @@ static noinline struct extent_buffer *read_node_slot(struct btrfs_root *root,
 
         eb = read_tree_block(root, btrfs_node_blockptr(parent, slot),
                              btrfs_node_ptr_generation(parent, slot));
-        if (eb && !extent_buffer_uptodate(eb)) {
-                free_extent_buffer(eb);
+        if (IS_ERR(eb) || !extent_buffer_uptodate(eb)) {
+                if (!IS_ERR(eb))
+                        free_extent_buffer(eb);
                 eb = NULL;
         }
 
@@ -2494,7 +2498,7 @@ read_block_for_search(struct btrfs_trans_handle *trans,
 
         ret = -EAGAIN;
         tmp = read_tree_block(root, blocknr, 0);
-        if (tmp) {
+        if (!IS_ERR(tmp)) {
                 /*
                  * If the read above didn't mark this buffer up to date,
                  * it will never end up being up to date.  Set ret to EIO now
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 2ef9a4b72d06..7f8377871283 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1149,12 +1149,12 @@ struct extent_buffer *read_tree_block(struct btrfs_root *root, u64 bytenr,
 
         buf = btrfs_find_create_tree_block(root, bytenr);
         if (!buf)
-                return NULL;
+                return ERR_PTR(-ENOMEM);
 
         ret = btree_read_extent_buffer_pages(root, buf, 0, parent_transid);
         if (ret) {
                 free_extent_buffer(buf);
-                return NULL;
+                return ERR_PTR(ret);
         }
         return buf;
 
@@ -1509,20 +1509,19 @@ static struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root,
         generation = btrfs_root_generation(&root->root_item);
         root->node = read_tree_block(root, btrfs_root_bytenr(&root->root_item),
                                      generation);
-        if (!root->node) {
-                ret = -ENOMEM;
+        if (IS_ERR(root->node)) {
+                ret = PTR_ERR(root->node);
                 goto find_fail;
         } else if (!btrfs_buffer_uptodate(root->node, generation, 0)) {
                 ret = -EIO;
-                goto read_fail;
+                free_extent_buffer(root->node);
+                goto find_fail;
         }
         root->commit_root = btrfs_root_node(root);
 out:
         btrfs_free_path(path);
         return root;
 
-read_fail:
-        free_extent_buffer(root->node);
 find_fail:
         kfree(root);
 alloc_fail:
@@ -2320,8 +2319,11 @@ static int btrfs_replay_log(struct btrfs_fs_info *fs_info,
 
         log_tree_root->node = read_tree_block(tree_root, bytenr,
                         fs_info->generation + 1);
-        if (!log_tree_root->node ||
-            !extent_buffer_uptodate(log_tree_root->node)) {
+        if (IS_ERR(log_tree_root->node)) {
+                printk(KERN_ERR "BTRFS: failed to read log tree\n");
+                kfree(log_tree_root);
+                return PTR_ERR(log_tree_root->node);
+        } else if (!extent_buffer_uptodate(log_tree_root->node)) {
                 printk(KERN_ERR "BTRFS: failed to read log tree\n");
                 free_extent_buffer(log_tree_root->node);
                 kfree(log_tree_root);
@@ -2797,8 +2799,8 @@ int open_ctree(struct super_block *sb,
         chunk_root->node = read_tree_block(chunk_root,
                                            btrfs_super_chunk_root(disk_super),
                                            generation);
-        if (!chunk_root->node ||
-            !test_bit(EXTENT_BUFFER_UPTODATE, &chunk_root->node->bflags)) {
+        if (IS_ERR(chunk_root->node) ||
+            !extent_buffer_uptodate(chunk_root->node)) {
                 printk(KERN_ERR "BTRFS: failed to read chunk root on %s\n",
                        sb->s_id);
                 goto fail_tree_roots;
@@ -2834,8 +2836,8 @@ retry_root_backup:
         tree_root->node = read_tree_block(tree_root,
                                           btrfs_super_root(disk_super),
                                           generation);
-        if (!tree_root->node ||
-            !test_bit(EXTENT_BUFFER_UPTODATE, &tree_root->node->bflags)) {
+        if (IS_ERR(tree_root->node) ||
+            !extent_buffer_uptodate(tree_root->node)) {
                 printk(KERN_WARNING "BTRFS: failed to read tree root on %s\n",
                        sb->s_id);
 
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 076fd7484a82..f1d1216f7feb 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7979,9 +7979,12 @@ walk_down:
                         child_gen = btrfs_node_ptr_generation(eb, parent_slot);
 
                         eb = read_tree_block(root, child_bytenr, child_gen);
-                        if (!eb || !extent_buffer_uptodate(eb)) {
-                                ret = -EIO;
+                        if (IS_ERR(eb)) {
+                                ret = PTR_ERR(eb);
+                                goto out;
+                        } else if (!extent_buffer_uptodate(eb)) {
                                 free_extent_buffer(eb);
+                                ret = -EIO;
                                 goto out;
                         }
 
@@ -8211,7 +8214,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
                 if (reada && level == 1)
                         reada_walk_down(trans, root, wc, path);
                 next = read_tree_block(root, bytenr, generation);
-                if (!next || !extent_buffer_uptodate(next)) {
+                if (IS_ERR(next)) {
+                        return PTR_ERR(next);
+                } else if (!extent_buffer_uptodate(next)) {
                         free_extent_buffer(next);
                         return -EIO;
                 }
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 74b24b01d574..827951fbf7fc 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1847,8 +1847,10 @@ again:
                         }
 
                         eb = read_tree_block(dest, old_bytenr, old_ptr_gen);
-                        if (!eb || !extent_buffer_uptodate(eb)) {
-                                ret = (!eb) ? -ENOMEM : -EIO;
+                        if (IS_ERR(eb)) {
+                                ret = PTR_ERR(eb);
+                        } else if (!extent_buffer_uptodate(eb)) {
+                                ret = -EIO;
                                 free_extent_buffer(eb);
                                 break;
                         }
@@ -2002,7 +2004,9 @@ int walk_down_reloc_tree(struct btrfs_root *root, struct btrfs_path *path,
 
                 bytenr = btrfs_node_blockptr(eb, path->slots[i]);
                 eb = read_tree_block(root, bytenr, ptr_gen);
-                if (!eb || !extent_buffer_uptodate(eb)) {
+                if (IS_ERR(eb)) {
+                        return PTR_ERR(eb);
+                } else if (!extent_buffer_uptodate(eb)) {
                         free_extent_buffer(eb);
                         return -EIO;
                 }
@@ -2710,7 +2714,10 @@ static int do_relocation(struct btrfs_trans_handle *trans,
                 blocksize = root->nodesize;
                 generation = btrfs_node_ptr_generation(upper->eb, slot);
                 eb = read_tree_block(root, bytenr, generation);
-                if (!eb || !extent_buffer_uptodate(eb)) {
+                if (IS_ERR(eb)) {
+                        err = PTR_ERR(eb);
+                        goto next;
+                } else if (!extent_buffer_uptodate(eb)) {
                         free_extent_buffer(eb);
                         err = -EIO;
                         goto next;
@@ -2873,7 +2880,9 @@ static int get_tree_block_key(struct reloc_control *rc,
         BUG_ON(block->key_ready);
         eb = read_tree_block(rc->extent_root, block->bytenr,
                              block->key.offset);
-        if (!eb || !extent_buffer_uptodate(eb)) {
+        if (IS_ERR(eb)) {
+                return PTR_ERR(eb);
+        } else if (!extent_buffer_uptodate(eb)) {
                 free_extent_buffer(eb);
                 return -EIO;
         }