Re: [PATCH v2 1/2] nfsd: handle failure to collect pre/post-op attrs more sanely

[NeilBrown]

On Fri, 21 Jul 2023, Jeff Layton wrote:
> Collecting pre_op_attrs can fail, in which case it's probably best to
> fail the whole operation.
> 
> Change fh_fill_{pre,post,both}_attrs to return __be32. For the pre and
> both functions, have the callers check the return code and abort the
> operation if it failed.
> 
> If fh_fill_post_attrs fails, then it's too late to do anything about it,
> so most of those callers ignore the return value. If this happens, then
> fh_post_saved will be false, which should cue the later stages to deal
> with it.
> 
> Suggested-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  fs/nfsd/nfs3proc.c |  4 +++-
>  fs/nfsd/nfs4proc.c | 14 ++++++------
>  fs/nfsd/nfsfh.c    | 26 ++++++++++++++---------
>  fs/nfsd/nfsfh.h    |  6 +++---
>  fs/nfsd/vfs.c      | 62 ++++++++++++++++++++++++++++++++++--------------------
>  5 files changed, 69 insertions(+), 43 deletions(-)
> 
> diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
> index fc8d5b7db9f8..268ef57751c4 100644
> --- a/fs/nfsd/nfs3proc.c
> +++ b/fs/nfsd/nfs3proc.c
> @@ -307,7 +307,9 @@ nfsd3_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  	if (!IS_POSIXACL(inode))
>  		iap->ia_mode &= ~current_umask();
>  
> -	fh_fill_pre_attrs(fhp);
> +	status = fh_fill_pre_attrs(fhp);
> +	if (status != nfs_ok)
> +		goto out;
>  	host_err = vfs_create(&nop_mnt_idmap, inode, child, iap->ia_mode, true);
>  	if (host_err < 0) {
>  		status = nfserrno(host_err);
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index d8e7a533f9d2..9285e1eab4d5 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -297,12 +297,12 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  	}
>  
>  	if (d_really_is_positive(child)) {
> -		status = nfs_ok;
> -
>  		/* NFSv4 protocol requires change attributes even though
>  		 * no change happened.
>  		 */
> -		fh_fill_both_attrs(fhp);
> +		status = fh_fill_both_attrs(fhp);
> +		if (status != nfs_ok)
> +			goto out;
>  
>  		switch (open->op_createmode) {
>  		case NFS4_CREATE_UNCHECKED:
> @@ -345,7 +345,9 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  	if (!IS_POSIXACL(inode))
>  		iap->ia_mode &= ~current_umask();
>  
> -	fh_fill_pre_attrs(fhp);
> +	status = fh_fill_pre_attrs(fhp);
> +	if (status != nfs_ok)
> +		goto out;
>  	status = nfsd4_vfs_create(fhp, child, open);
>  	if (status != nfs_ok)
>  		goto out;
> @@ -424,11 +426,11 @@ do_open_lookup(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, stru
>  	} else {
>  		status = nfsd_lookup(rqstp, current_fh,
>  				     open->op_fname, open->op_fnamelen, *resfh);
> -		if (!status)
> +		if (status == nfs_ok)
>  			/* NFSv4 protocol requires change attributes even though
>  			 * no change happened.
>  			 */
> -			fh_fill_both_attrs(current_fh);
> +			status = fh_fill_both_attrs(current_fh);
>  	}
>  	if (status)
>  		goto out;
> diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> index c291389a1d71..f7e68a91e826 100644
> --- a/fs/nfsd/nfsfh.c
> +++ b/fs/nfsd/nfsfh.c
> @@ -614,7 +614,7 @@ fh_update(struct svc_fh *fhp)
>   * @fhp: file handle to be updated
>   *
>   */
> -void fh_fill_pre_attrs(struct svc_fh *fhp)
> +__be32 fh_fill_pre_attrs(struct svc_fh *fhp)
>  {
>  	bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
>  	struct inode *inode;
> @@ -622,12 +622,12 @@ void fh_fill_pre_attrs(struct svc_fh *fhp)
>  	__be32 err;
>  
>  	if (fhp->fh_no_wcc || fhp->fh_pre_saved)
> -		return;
> +		return nfs_ok;
>  
>  	inode = d_inode(fhp->fh_dentry);
>  	err = fh_getattr(fhp, &stat);
>  	if (err)
> -		return;
> +		return err;
>  
>  	if (v4)
>  		fhp->fh_pre_change = nfsd4_change_attribute(&stat, inode);
> @@ -636,6 +636,7 @@ void fh_fill_pre_attrs(struct svc_fh *fhp)
>  	fhp->fh_pre_ctime = stat.ctime;
>  	fhp->fh_pre_size  = stat.size;
>  	fhp->fh_pre_saved = true;
> +	return nfs_ok;
>  }
>  
>  /**
> @@ -643,26 +644,27 @@ void fh_fill_pre_attrs(struct svc_fh *fhp)
>   * @fhp: file handle to be updated
>   *
>   */
> -void fh_fill_post_attrs(struct svc_fh *fhp)
> +__be32 fh_fill_post_attrs(struct svc_fh *fhp)
>  {
>  	bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
>  	struct inode *inode = d_inode(fhp->fh_dentry);
>  	__be32 err;
>  
>  	if (fhp->fh_no_wcc)
> -		return;
> +		return nfs_ok;
>  
>  	if (fhp->fh_post_saved)
>  		printk("nfsd: inode locked twice during operation.\n");
>  
>  	err = fh_getattr(fhp, &fhp->fh_post_attr);
>  	if (err)
> -		return;
> +		return err;
>  
>  	fhp->fh_post_saved = true;
>  	if (v4)
>  		fhp->fh_post_change =
>  			nfsd4_change_attribute(&fhp->fh_post_attr, inode);
> +	return nfs_ok;
>  }
>  
>  /**
> @@ -672,16 +674,20 @@ void fh_fill_post_attrs(struct svc_fh *fhp)
>   * This is used when the directory wasn't changed, but wcc attributes
>   * are needed anyway.
>   */
> -void fh_fill_both_attrs(struct svc_fh *fhp)
> +__be32 fh_fill_both_attrs(struct svc_fh *fhp)
>  {
> -	fh_fill_post_attrs(fhp);
> -	if (!fhp->fh_post_saved)
> -		return;
> +	__be32 err;
> +
> +	err = fh_fill_post_attrs(fhp);
> +	if (err)
> +		return err;
> +
>  	fhp->fh_pre_change = fhp->fh_post_change;
>  	fhp->fh_pre_mtime = fhp->fh_post_attr.mtime;
>  	fhp->fh_pre_ctime = fhp->fh_post_attr.ctime;
>  	fhp->fh_pre_size = fhp->fh_post_attr.size;
>  	fhp->fh_pre_saved = true;
> +	return nfs_ok;
>  }
>  
>  /*
> diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
> index 4e0ecf0ae2cf..486803694acc 100644
> --- a/fs/nfsd/nfsfh.h
> +++ b/fs/nfsd/nfsfh.h
> @@ -294,7 +294,7 @@ static inline void fh_clear_pre_post_attrs(struct svc_fh *fhp)
>  }
>  
>  u64 nfsd4_change_attribute(struct kstat *stat, struct inode *inode);
> -extern void fh_fill_pre_attrs(struct svc_fh *fhp);
> -extern void fh_fill_post_attrs(struct svc_fh *fhp);
> -extern void fh_fill_both_attrs(struct svc_fh *fhp);
> +__be32 fh_fill_pre_attrs(struct svc_fh *fhp);
> +__be32 fh_fill_post_attrs(struct svc_fh *fhp);
> +__be32 fh_fill_both_attrs(struct svc_fh *fhp);
>  #endif /* _LINUX_NFSD_NFSFH_H */
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 8a2321d19194..f200afd33630 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1537,9 +1537,11 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  	dput(dchild);
>  	if (err)
>  		goto out_unlock;
> -	fh_fill_pre_attrs(fhp);
> -	err = nfsd_create_locked(rqstp, fhp, attrs, type, rdev, resfhp);
> -	fh_fill_post_attrs(fhp);
> +	err = fh_fill_pre_attrs(fhp);
> +	if (err == nfs_ok) {
> +		err = nfsd_create_locked(rqstp, fhp, attrs, type, rdev, resfhp);
> +		fh_fill_post_attrs(fhp);

Most error handling in nfsd is
 
   if (err)
       goto ....

Here (and one other place I think) you have
   if (not err)
       do stuff;

Do we want to be more consistent?  I'm in two minds about this and I
don't dislike your patch.  But I noticed the inconsistency and thought I
should mention it.

Also, should we put a __must_check annotation on fh_fill_pre_attrs() and
..post..?  Then I wouldn't have to manually check that you found and
fixed all callers (which I haven't).

Thanks,
NeilBrown