[SRU][UNSTABLE][PATCH 1/2] UBUNTU: SAUCE: Revert "UBUNTU: SAUCE: shiftfs: fix dentry revalidation"

[Christian Brauner]

On Wed, Jun 24, 2020 at 12:14:38PM +0200, Christian Brauner wrote:
> BugLink: https://bugs.launchpad.net/bugs/1884767
> 
> With patch cfaa482afb97 ("UBUNTU: SAUCE: shiftfs: fix dentry revalidation")
> we tried to fix
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1872757 but it
> introduces a regression for shiftfs on btrfs users. Creating a btrfs
> subvolume, deleting it, and then trying to recreate it will cause EEXIST
> to be returned or the file be left in a half-created state. Faulty
> behavior such as this can be reproduced via:
> 
> btrfs subvolume create my-subvol
> ls -al my-subvol
> btrfs subvolume delete my-subvol
> 
> We thus need to revert this change restoring the old behavior.This will
> briefly resurface https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1872757
> which is fixed in a follow-up patch on top of this revert. We simply
> split out the minimal fix into a separate tiny patch.
> 
> This reverts commit de1ac7ed38fd68183fc34d58aaf9f0609890caae.
> 
> Cc: Seth Forshee <seth.forshee at canonical.com>
> Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
> ---

Seth,

Just for your interest: Disco does not have the problematic patch
afaict. So with Eoan, Focal, and Unstable we should be good!
(All patches should be on top of the latest tag I could find.)

Thanks!
Christian

>  fs/shiftfs.c | 45 ++++++++++++++++++++++++++++++++-------------
>  1 file changed, 32 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/shiftfs.c b/fs/shiftfs.c
> index 36ac45a6d835..f9a5c94a9793 100644
> --- a/fs/shiftfs.c
> +++ b/fs/shiftfs.c
> @@ -241,17 +241,19 @@ static int shiftfs_d_weak_revalidate(struct dentry *dentry, unsigned int flags)
>  	int err = 1;
>  	struct dentry *lowerd = dentry->d_fsdata;
>  
> -	if (lowerd->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
> +	if (d_is_negative(lowerd) != d_is_negative(dentry))
> +		return 0;
> +
> +	if ((lowerd->d_flags & DCACHE_OP_WEAK_REVALIDATE))
>  		err = lowerd->d_op->d_weak_revalidate(lowerd, flags);
> -		if (err < 0)
> -			return err;
> -	}
>  
>  	if (d_really_is_positive(dentry)) {
>  		struct inode *inode = d_inode(dentry);
>  		struct inode *loweri = d_inode(lowerd);
>  
>  		shiftfs_copyattr(loweri, inode);
> +		if (!inode->i_nlink)
> +			err = 0;
>  	}
>  
>  	return err;
> @@ -262,25 +264,23 @@ static int shiftfs_d_revalidate(struct dentry *dentry, unsigned int flags)
>  	int err = 1;
>  	struct dentry *lowerd = dentry->d_fsdata;
>  
> +	if (d_unhashed(lowerd) ||
> +	    ((d_is_negative(lowerd) != d_is_negative(dentry))))
> +		return 0;
> +
>  	if (flags & LOOKUP_RCU)
>  		return -ECHILD;
>  
> -	if (lowerd->d_flags & DCACHE_OP_REVALIDATE) {
> +	if ((lowerd->d_flags & DCACHE_OP_REVALIDATE))
>  		err = lowerd->d_op->d_revalidate(lowerd, flags);
> -		if (err < 0)
> -			return err;
> -		if (!err) {
> -			if (!(flags & LOOKUP_RCU))
> -				d_invalidate(lowerd);
> -			return -ESTALE;
> -		}
> -	}
>  
>  	if (d_really_is_positive(dentry)) {
>  		struct inode *inode = d_inode(dentry);
>  		struct inode *loweri = d_inode(lowerd);
>  
>  		shiftfs_copyattr(loweri, inode);
> +		if (!inode->i_nlink)
> +			err = 0;
>  	}
>  
>  	return err;
> @@ -737,6 +737,24 @@ static int shiftfs_fiemap(struct inode *inode,
>  	return err;
>  }
>  
> +static int shiftfs_tmpfile(struct inode *dir, struct dentry *dentry,
> +			   umode_t mode)
> +{
> +	int err;
> +	const struct cred *oldcred;
> +	struct dentry *lowerd = dentry->d_fsdata;
> +	struct inode *loweri = dir->i_private;
> +
> +	if (!loweri->i_op->tmpfile)
> +		return -EOPNOTSUPP;
> +
> +	oldcred = shiftfs_override_creds(dir->i_sb);
> +	err = loweri->i_op->tmpfile(loweri, lowerd, mode);
> +	revert_creds(oldcred);
> +
> +	return err;
> +}
> +
>  static int shiftfs_setattr(struct dentry *dentry, struct iattr *attr)
>  {
>  	struct dentry *lowerd = dentry->d_fsdata;
> @@ -1003,6 +1021,7 @@ static const struct inode_operations shiftfs_file_inode_operations = {
>  	.listxattr	= shiftfs_listxattr,
>  	.permission	= shiftfs_permission,
>  	.setattr	= shiftfs_setattr,
> +	.tmpfile	= shiftfs_tmpfile,
>  };
>  
>  static const struct inode_operations shiftfs_special_inode_operations = {
> 
> base-commit: eed567f60e03230138081b3ae955cbded06c32e9
> -- 
> 2.27.0
>