Josef Bacik <jbacik@xxxxxx> writes:
> A user was running into errors from an NFS export of a subvolume that had a
> default subvol set. When we mount a default subvol we will use d_obtain_alias()
> to find an existing dentry for the subvolume in the case that the root subvol
> has already been mounted, or a dummy one is allocated in the case that the root
> subvol has not already been mounted. This allows us to connect the dentry later
> on if we wander into the path. However if we don't ever wander into the path we
> will keep DCACHE_DISCONNECTED set for a long time, which angers NFS. It doesn't
> appear to cause any problems but it is annoying nonetheless, so simply unset
> DCACHE_DISCONNECTED in the get_default_root case and switch btrfs_lookup() to
> use d_materialise_unique() instead which will make everything play nicely
> together and reconnect stuff if we wander into the defaul subvol path from a
> different way. With this patch I'm no longer getting the NFS errors when
> exporting a volume that has been mounted with a default subvol set. Thanks,
>
> cc: bfields@xxxxxxxxxxxx
> cc: ebiederm@xxxxxxxxxxxx
Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> Signed-off-by: Josef Bacik <jbacik@xxxxxx>
> ---
> fs/btrfs/inode.c | 2 +-
> fs/btrfs/super.c | 9 ++++++++-
> 2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 197edee..8dba152 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -5157,7 +5157,7 @@ static struct dentry *btrfs_lookup(struct inode *dir, struct dentry *dentry,
> return ERR_CAST(inode);
> }
>
> - return d_splice_alias(inode, dentry);
> + return d_materialise_unique(dentry, inode);
> }
>
> unsigned char btrfs_filetype_table[] = {
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 147ca1d..dc0a315 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -855,6 +855,7 @@ static struct dentry *get_default_root(struct super_block *sb,
> struct btrfs_path *path;
> struct btrfs_key location;
> struct inode *inode;
> + struct dentry *dentry;
> u64 dir_id;
> int new = 0;
>
> @@ -925,7 +926,13 @@ setup_root:
> return dget(sb->s_root);
> }
>
> - return d_obtain_alias(inode);
> + dentry = d_obtain_alias(inode);
> + if (!IS_ERR(dentry)) {
> + spin_lock(&dentry->d_lock);
> + dentry->d_flags &= ~DCACHE_DISCONNECTED;
> + spin_unlock(&dentry->d_lock);
> + }
> + return dentry;
> }
>
> static int btrfs_fill_super(struct super_block *sb,
--
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