Re: [PATCH 1/7] ovl: update of dentry revalidate flags after copy up

[Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>]

On 2023/4/9 00:42, Amir Goldstein wrote:
> After copy up, we may need to update d_flags if upper dentry is on a
> remote fs and lower dentries are not.
>
> Add helpers to allow incremental update of the revalidate flags.
>
> Fixes: bccece1ead36 ("ovl: allow remote upper")
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

> ---
>   fs/overlayfs/copy_up.c   |  2 ++
>   fs/overlayfs/dir.c       |  3 +--
>   fs/overlayfs/export.c    |  3 +--
>   fs/overlayfs/namei.c     |  3 +--
>   fs/overlayfs/overlayfs.h |  6 ++++--
>   fs/overlayfs/super.c     |  2 +-
>   fs/overlayfs/util.c      | 24 ++++++++++++++++++++----
>   7 files changed, 30 insertions(+), 13 deletions(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index c14e90764e35..7bf101e756c8 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -576,6 +576,7 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
>   			/* Restore timestamps on parent (best effort) */
>   			ovl_set_timestamps(ofs, upperdir, &c->pstat);
>   			ovl_dentry_set_upper_alias(c->dentry);
> +			ovl_dentry_update_reval(c->dentry, upper);
>   		}
>   	}
>   	inode_unlock(udir);
> @@ -895,6 +896,7 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
>   		inode_unlock(udir);
>   
>   		ovl_dentry_set_upper_alias(c->dentry);
> +		ovl_dentry_update_reval(c->dentry, ovl_dentry_upper(c->dentry));
>   	}
>   
>   out:
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index fc25fb95d5fc..9be52d8013c8 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -269,8 +269,7 @@ static int ovl_instantiate(struct dentry *dentry, struct inode *inode,
>   
>   	ovl_dir_modified(dentry->d_parent, false);
>   	ovl_dentry_set_upper_alias(dentry);
> -	ovl_dentry_update_reval(dentry, newdentry,
> -			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
> +	ovl_dentry_init_reval(dentry, newdentry);
>   
>   	if (!hardlink) {
>   		/*
> diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
> index defd4e231ad2..5c36fb3a7bab 100644
> --- a/fs/overlayfs/export.c
> +++ b/fs/overlayfs/export.c
> @@ -326,8 +326,7 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
>   	if (upper_alias)
>   		ovl_dentry_set_upper_alias(dentry);
>   
> -	ovl_dentry_update_reval(dentry, upper,
> -			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
> +	ovl_dentry_init_reval(dentry, upper);
>   
>   	return d_instantiate_anon(dentry, inode);
>   
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index cfb3420b7df0..100a492d2b2a 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -1122,8 +1122,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
>   			ovl_set_flag(OVL_UPPERDATA, inode);
>   	}
>   
> -	ovl_dentry_update_reval(dentry, upperdentry,
> -			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
> +	ovl_dentry_init_reval(dentry, upperdentry);
>   
>   	revert_creds(old_cred);
>   	if (origin_path) {
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 4d0b278f5630..e100c55bb924 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -375,8 +375,10 @@ bool ovl_index_all(struct super_block *sb);
>   bool ovl_verify_lower(struct super_block *sb);
>   struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
>   bool ovl_dentry_remote(struct dentry *dentry);
> -void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *upperdentry,
> -			     unsigned int mask);
> +void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *realdentry);
> +void ovl_dentry_init_reval(struct dentry *dentry, struct dentry *upperdentry);
> +void ovl_dentry_init_flags(struct dentry *dentry, struct dentry *upperdentry,
> +			   unsigned int mask);
>   bool ovl_dentry_weird(struct dentry *dentry);
>   enum ovl_path_type ovl_path_type(struct dentry *dentry);
>   void ovl_path_upper(struct dentry *dentry, struct path *path);
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index f1d9f75f8786..49b6956468f9 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1885,7 +1885,7 @@ static struct dentry *ovl_get_root(struct super_block *sb,
>   	ovl_dentry_set_flag(OVL_E_CONNECTED, root);
>   	ovl_set_upperdata(d_inode(root));
>   	ovl_inode_init(d_inode(root), &oip, ino, fsid);
> -	ovl_dentry_update_reval(root, upperdentry, DCACHE_OP_WEAK_REVALIDATE);
> +	ovl_dentry_init_flags(root, upperdentry, DCACHE_OP_WEAK_REVALIDATE);
>   
>   	return root;
>   }
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index 923d66d131c1..6a0652bd51f2 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -94,14 +94,30 @@ struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
>   	return oe;
>   }
>   
> +#define OVL_D_REVALIDATE (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE)
> +
>   bool ovl_dentry_remote(struct dentry *dentry)
>   {
> -	return dentry->d_flags &
> -		(DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
> +	return dentry->d_flags & OVL_D_REVALIDATE;
> +}
> +
> +void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *realdentry)
> +{
> +	if (!ovl_dentry_remote(realdentry))
> +		return;
> +
> +	spin_lock(&dentry->d_lock);
> +	dentry->d_flags |= realdentry->d_flags & OVL_D_REVALIDATE;

Although I'm not sure if it could cause some lazy awareness due to dcache
RCU-walk, but maybe that is fine since such window is small?

Thanks,
Gao Xiang