Btrfs: setup blank root and fs_info for mount time

There is a problem with how we use sget, it searches through the list of supers
attached to the fs_type looking for a super with the same fs_devices as what
we're trying to mount.  This depends on sb->s_fs_info being filled, but we don't
fill that in until we get to btrfs_fill_super, so we could hit supers on the
fs_type super list that have a null s_fs_info.  In order to fix that we need to
go ahead and setup a blank root with a blank fs_info to hold fs_devices, that
way our test will work out right and then we can set s_fs_info in
btrfs_set_super, and then open_ctree will simply use our pre-allocated root and
fs_info when setting everything up.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

2 files changed, 33 insertions, 7 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a67b98d58c2a..57c9d8eeb7dc 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1561,10 +1561,8 @@ struct btrfs_root *open_ctree(struct super_block *sb,
                                                  GFP_NOFS);
         struct btrfs_root *csum_root = kzalloc(sizeof(struct btrfs_root),
                                                  GFP_NOFS);
-        struct btrfs_root *tree_root = kzalloc(sizeof(struct btrfs_root),
-                                               GFP_NOFS);
-        struct btrfs_fs_info *fs_info = kzalloc(sizeof(*fs_info),
-                                                GFP_NOFS);
+        struct btrfs_root *tree_root = btrfs_sb(sb);
+        struct btrfs_fs_info *fs_info = tree_root->fs_info;
         struct btrfs_root *chunk_root = kzalloc(sizeof(struct btrfs_root),
                                                 GFP_NOFS);
         struct btrfs_root *dev_root = kzalloc(sizeof(struct btrfs_root),
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 141fb317d3bc..47bf67cbe6bf 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -563,7 +563,7 @@ static int btrfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
 
 static int btrfs_test_super(struct super_block *s, void *data)
 {
-        struct btrfs_fs_devices *test_fs_devices = data;
+        struct btrfs_root *test_root = data;
         struct btrfs_root *root = btrfs_sb(s);
 
         /*
@@ -572,9 +572,17 @@ static int btrfs_test_super(struct super_block *s, void *data)
          */
         if (!atomic_read(&s->s_active))
                 return 0;
-        return root->fs_info->fs_devices == test_fs_devices;
+        return root->fs_info->fs_devices == test_root->fs_info->fs_devices;
 }
 
+static int btrfs_set_super(struct super_block *s, void *data)
+{
+        s->s_fs_info = data;
+
+        return set_anon_super(s, data);
+}
+
+
 /*
  * Find a superblock for the given device / mount point.
  *
@@ -588,6 +596,8 @@ static int btrfs_get_sb(struct file_system_type *fs_type, int flags,
         struct super_block *s;
         struct dentry *root;
         struct btrfs_fs_devices *fs_devices = NULL;
+        struct btrfs_root *tree_root = NULL;
+        struct btrfs_fs_info *fs_info = NULL;
         fmode_t mode = FMODE_READ;
         char *subvol_name = NULL;
         u64 subvol_objectid = 0;
@@ -615,8 +625,24 @@ static int btrfs_get_sb(struct file_system_type *fs_type, int flags,
                 goto error_close_devices;
         }
 
+        /*
+         * Setup a dummy root and fs_info for test/set super.  This is because
+         * we don't actually fill this stuff out until open_ctree, but we need
+         * it for searching for existing supers, so this lets us do that and
+         * then open_ctree will properly initialize everything later.
+         */
+        fs_info = kzalloc(sizeof(struct btrfs_fs_info), GFP_NOFS);
+        tree_root = kzalloc(sizeof(struct btrfs_root), GFP_NOFS);
+        if (!fs_info || !tree_root) {
+                error = -ENOMEM;
+                goto error_close_devices;
+        }
+        fs_info->tree_root = tree_root;
+        fs_info->fs_devices = fs_devices;
+        tree_root->fs_info = fs_info;
+
         bdev = fs_devices->latest_bdev;
-        s = sget(fs_type, btrfs_test_super, set_anon_super, fs_devices);
+        s = sget(fs_type, btrfs_test_super, btrfs_set_super, tree_root);
         if (IS_ERR(s))
                 goto error_s;
 
@@ -685,6 +711,8 @@ error_s:
         error = PTR_ERR(s);
 error_close_devices:
         btrfs_close_devices(fs_devices);
+        kfree(fs_info);
+        kfree(tree_root);
 error_free_subvol_name:
         kfree(subvol_name);
         return error;